Sunday, July 16, 2017
Issue #544: To PEC or not to PEC
|Me and my trusty Ultima 8 PEC circa 1995...|
If you read the last installment of the good old Astro Blog, you know I am a proponent of shorter (60 – 120-second) sub-frame exposures for astrophotography. When appropriate. Like from a light polluted site. There are times when you want to go longer, to 300-second or 600-second or longer sub-frames, however. Say when you are at your dark site and want to pick up as many details in the target object as possible.
Some of you, especially cheapskates like me who use inexpensive mounts like my Celestron Advanced VX German equatorial mount (GEM), are afraid of longer exposures. How can you break the 300-second barrier without getting trailed stars? There are ways to do that fairly easily. Good polar alignment is one. Spending time tweaking the settings in your auto-guide program is another. One other thing that is often overlooked and unused, but which can maybe get you the last step on the road to longer subs, is PEC.
Yeah, PEC, aka “PPEC.” You know what that is doncha? You don’t? Well, PEC, “periodic error correction,” was an idea that came out of the early 1990s, when microprocessors and memory chips not only came down in price, but began to appear in telescopes. I don’t know who originally came up with the idea, but it was a good one.
In those days, we amateurs were still guiding manually. You’d monitor a guide star in the guide scope or off axis guider with a cross-hair reticle eyepiece. When the star wandered away from the center due to the inevitable “periodic” errors in the mount’s gears, or drifted north or south due to polar alignment error, you pushed a button on the hand control (which we still called a hand “paddle”) to move that pesky star back to the cross-hairs. You did this over the duration of a long deep sky photographic exposure, which in the days of film was likely at least half an hour.
The good idea represented by PEC was this: What if there were a way to record your button pushes? Record your corrections for that periodic error and play them back? That would, if nothing else, make guiding easier. Thanks to the recurring—periodic—nature of the gear error in worm gear sets, which is what most of us were using by then, it sounded like PEC could indeed work.
Again, I am not sure who came up with the PEC idea, but the first people to implement it in a commercial telescope were Celestron, the old American based (though Swiss owned) Celestron out of Torrance, California. They brought PEC to the market initially with their top of the line C8 Schmidt Cassegrain, the Ultima 8, in a new version of the telescope, the Ultima 8 PEC.
It just so happened that not long after the final and best version of that telescope was released, the 9-volt battery powered Ultima 8 (PEC), I was in the market for a slightly upscale SCT. Well, as upscale as penny-pinching me ever goes. By the spring of 1995, I finally had an Ultima of my own, and after buying a few rather expensive (I thought) accessories like a declination drive motor (optional in those days) and a counterweight and rail for this fork mount scope, I undertook to do some deep sky imaging. I was curious to see if PEC really took the pain out of guiding.
|Phd2 guiding graph: VX with auto-guiding + PPEC...|
What I found was that it helped. You certainly could not expect to go unguided with the C8 at 1500mm (at f/6.3) for over a minute or two—not long enough to accomplish much with film—but it did make guiding less arduous. You still had to watch the guide star, but if you did a good PEC recording, you would usually be OK if you looked away from the reticle for a moment or your attention wandered. The periodic error was still there, but its magnitude was lessened.
Celestron’s PEC implementation was certainly not the end of manual guiding. Naturally, it only recorded your east-west corrections. Any errors in declination are not periodic; they are due to polar alignment error or seeing, not periodic error. Too bad I was always rather lazy about polar alignment in those days. That meant I still had to monitor the guide star attentively.
Also, Celestron’s version of PEC left a little to be desired. Mainly because you had to do a brand-new recording every single night. It was a shame you couldn’t save an especially good PEC track for future use. Turn off the scope at the end of the evening, and your PEC recording disappeared into the ozone.
Nevertheless, I used PEC to the end of the film days, and it did improve my photos, no doubt about that. But when electronic cameras and auto-guiding came in, I forgot all about PEC. Yes, there had been improvements in it—Meade and, finally, Celestron had equipped their mounts with PPEC, permanent periodic error correction. With PPEC, your recording was preserved through power cycles. But why worry with PEC since you had a guide camera and a computer watching that guide star now?
There was also an old wives’ tale making the rounds. That PEC and an auto-guider would FIGHT each other. That the auto guider and PEC would conflict, one wanting to correct this much and the other that much; one wanting to go in this direction, and the other in that. Some of those old wives were pretty sharp, but this particular tale doesn’t really make a heck of a lot of sense when you think about it. Nevertheless, for a while it was the conventional wisdom astrophotographers embraced. I just sort of accepted it—when I thought about PPEC at all, which was seldom. I was auto-guiding and that always seemed to be enough.
|M13: 300-seconds at 900mm f/l...|
Well, I thought it was enough, anyway. Auto-guiding with my Advanced VX GEM with my QHY-5L II camera and PHD2 resulted in an RMS error around 2” usually. That was good enough for my most used telescopes, my 80mm and 120mm f/7 ED refractors and my DSLRs. There were some occasional R.A. spikes, though, and at times the error would climb above 2”.
What could I do to improve on that error figure? One thing I’d avoided doing since buying the VX: spending some time fine-tuning those blasted PHD2 brain settings, the settings in the program that modify the guiding algorithm. I’d pretty much left them on their defaults other than just increasing the guide-step size to accommodate my fast 50mm guide scope.
So, I finally buckled down and took one whole night where I did absolutely nothing but tweak PHD settings. The result? My guiding was now smoother. The spikes were gone, and I rarely had an error above 2”; usually it was 1.5” or just a bit more. The elimination of the spikes meant I could now do longer exposures without having to throw out more than a few subs.
And then I got to thinking. Why should I stop there? If I could get that error just a little lower, it would make imaging with my Edge 800 (at f/7) easier. But how to do that? I’d worked hard on those PHD settings, and had also begun using Sharpcap’s polar alignment tool in lieu of the less accurate ASPA polar alignment in the NexStar HC—that really brought the declination error down.
What else could I do, though? Well, how about PPEC? If it helped A-P’s fancy mounts, which come with factory recorded PPEC to lower their already impressive error figures, why couldn’t it help my plebian (like me) mount?
I decided to find out. Luckily, we were undergoing a strangely cloud-free pause in the usual summer evening thunderstorms. My VX along with my 120mm SkyWatcher ED refractor, Hermione, was still set up in the backyard, polar aligned, goto aligned (hibernated), and ready to rock following the night of my Yearly M13. Since the evening didn’t look that good for imaging—haze and also unsteady seeing in advance of the next storm front—why not devote it to PEC? After all, I’d spent a whole evening getting my PHD2 settings tuned to the VX.
OK, so how exactly would I make a latter-day PEC recording? I’d taken a brief look at the short set of instructions in the VX manual and concluded there really wasn’t much to it. The process wasn’t much different from back in the day except for the fact that PHD2 Guiding would be doing the “button pushing” and not me (thank God). Since I guide via the mount’s auto-guide port with an ST-4 cable, the set up was simple. No need to worry about ASCOM or anything like that.
While the book instructs you to use a bright star for guiding when PEC recording, there’s no reason for that with today’s sensitive guide cameras. I pointed the scope at the field of M57 and there were dozens of good guide star candidates. Some folks will also tell you that for best PEC results you need to make the recording using a star near the Celestial Equator. That is also untrue. It really doesn’t make any difference.
Step one, it appeared, was “indexing,” allowing the mount’s PEC routine to find the worm gear “index,” a marked point on the worm that is picked up by a sensor. For PEC to work, the hand control has to match the gear to the recording every time you use PEC, the gear and the recording must be synchronized. Indexing does that. Anyhow, I selected PEC in the Utility menu, and hit enter. The mount then indexed, which only took a second or two (if the worm has to rotate far to bring the index mark to the sensor, the mount will move slightly). Time to record.
Over at the PC, I started PHD2 guiding on my pre-selected guide star. I gave it a little while to settle down, returned to the mount, and hit “record.” That began the ten-minute process of making the actual PPEC recording. Unlike the old days, there wasn’t anything for me to do. Assured PHD2 was guiding with its usual alacrity, I headed for the den to cool off from the hot and muggy backyard.
The rest was rather anti-climactic. I returned outside ten minutes later, and could see from the HC that the recording was done. Just like with a tape recorder, you don’t just record, you play back. I selected the playback function and let her rip, beginning a 600 second exposure of M57 with the main camera, my Canon 400D.
What were the results? Error wise, they weren’t like night and day, but there was a difference. As above, my normal error level with good PHD2 settings and a good polar alignment had been around 1.5”. With PEC playback on, the RMS R.A. and declination error declined to around 1” to about 1.10” with the actual R.A. error almost always well under 1”. While I was slightly out of focus with the main telescope, the stars in the ten-minute exposure were decently round, as were the stars in a 300” exposure of M13 despite the fact that it had crossed the Meridian and the mount was not balanced properly in R.A. for imaging in the west. My verdict? Recording PEC had been nearly effortless and certainly worth it for a noticeable improvement.
Over the last several months, my easy improvements: PHD settings, polar alignment, and PEC have taken my AVX mount from an average total guiding error of 2 – 2.5” to 1”. While I was getting by before, I am certainly doing better now. And the fact that my guiding is now consistently smooth with no excursions mean I am much, much more able to undertake longer exposures, 300-seconds and above, when appropriate. My sense is that as long as balance is reasonable, the mount will guide at the above error level for as long as I want to go.
So, am I at the end of my improvements? Maybe, and maybe not. I could certainly leave the AVX alone now. But there is one further “easy” improvement I could essay. My single PEC recording improved the error figure. But averaging several runs and uploading that resulting smoothed curve to the mount might make it even better.
Celestron still offers a free program to do that, “Pec Tool” (even though it hasn’t been updated or publicized in a long time). I may be reaching the point of diminishing returns with the VX—1” RMS error is pretty good for a mount in this class—but it might be worthwhile to take this one last step. I’ll let you know how it goes if I decide to do that (ain’t broke/don’t fix it) and if clear skies ever return this summer. It is, yes, raining hard now.
Sunday, July 09, 2017
Issue #543: My Yearly M13 (from the backyard…)
One of my traditions is that each year, sometime over the course of the summer, I take a picture of star cluster Messier 13. Why? Well, it’s tradition as Tevye said. But it also ensures I get out at least once during the hot, humid, hazy, and usually stormy Gulf Coast summer and take a few deep sky pictures.
I’ll admit these days I am not sanguine about braving sweat and mosquito bites trying to get images from skies that look like milk. If I lay off until fall, however, I get out of practice. And as complex an endeavor as deep sky astrophotography is, you do not want to get out of practice.
Usually, I do my portrait of the Great Globular in Hercules from my dark site in the wilds of northwestern Mobile County. Not this year. With June already segueing into July and hurricane season threatening to get started in earnest, I thought I’d better get my M as soon as possible. The conditions were just lousy, though. So lousy that I had no intention of loading a ton of gear and driving half an hour to the dark site only to sit under clouds hoping for sucker holes while providing dinner for hordes of six-legged fiends. The good, old, backyard it would be.
Can you get decent photos of deep sky objects from the backyard? Yes, you can, and not just of the brighter objects, either. You’ll notice in the shots here that M13’s little “companion,” the near 12th magnitude galaxy NGC 6207, shows up readily and even gives up its nebulous disk. M13 itself and similar bright clusters are really no challenge. But whether you’re trying easy or hard from the back forty, what will lead to success is the understanding that imaging the deep sky from brighter skies is a battle.
This battle is between the target object and the bright background. While it is much easier to pull a washed-out object out of the light pollution today with electronic cameras and digital processing, it’s still best to minimize light pollution induced background brightness to the extent you can.
|Pac Man Nebula with "Imaging" LPR filter...|
One thing you can do to accomplish that is use a relatively slow telescope. Why? Have you ever tried a wide-field image from light pollution? If you have, you know it’s pretty hopeless. After little more than a minute—or maybe even less—the image appears to be of the daytime sky. Most (fixed focal length) camera lenses are so fast, f/2 or faster, that the background blows out in a hurry, before many details in the object you are wanting to image are recorded. So, slow it down. I like f/6 or, better, f/7 from the backyard.
How about filters? I’ve tried them, mild “imaging” LPR (light pollution reduction) filters, and it’s a mixed bag. I do find them helpful in capturing fainter nebulae. A filter allowed me to get a respectable image of the Pac Man Nebula from my yard on a not so good evening. There is a penalty, however—color shift. While the nebula was easy enough to color balance, when it was just right the stars were a distinct reddish hue due to the presence of the filter. On the other hand, I was able to get a better picture of the Pacmeister by far with than without the filter. I use a filter only when there is no alternative.
In the interest of keeping the background glow a little lower and not burning out—overexposing—the cores of globulars and similar objects with bright centers, I generally set my DSLR’s ISO no higher than 800. That is more than adequate to bring home faint nebulosity, and in addition to keeping the background less overpowering, it reduces the noise in my frames. Stacked ISO 800 frames are visibly less noisy than stacked ISO 1600 ones.
The big question, though? How long should your subframe exposures be and how many should you take? The latter is easy to answer: “As many as possible.” Each additional subframe added to a stack decreases noise and makes processing easier. Certainly, you shouldn’t keep exposing when the object reaches problem areas like the Meridian (for some mounts) and the horizon (for all mounts). But the more good subs you can get the better the results will be. Don’t be shy about throwing out poor subframes, of course—ones with trailed stars or aircraft or satellite intrusions. If you take lots of subs, it won’t be as painful if you have to delete a few.
How long should the individual exposures be? That’s harder. Longer exposures pick up more details and are less noisy than shorter ones. Remember, no matter how many frames you stack, no details not present in a single subframe will be visible in the finished, stacked image. So, the basic requisite is that you must expose long enough for desired details to be visible in individual frames.
|In a 1-minute exposure the background is brown...|
At a dark site, go as long as necessary, or as long as you and your mount can stand it exposure wise. In the backyard, though, you will be limited. Expose for much over a minute or two and the sky background will become incredibly bright and color shifted as in the picture below, a two-sub 300 second exposure with my f/7 120mm ED refractor, Celestron AVX mount, and Canon 400D. Processing can bring back a passable final result, especially when it comes to darkening the background, but fixing the light pollution caused color shift is a more serious and difficult problem.
As you can see in my final 300-second x two subs picture in the comparison shot below, M13 is noticeably (too) blue. I got the background unreddened using the “background color offset” function in Nebulosity, but that left M13 with a cool tinge. That can be fixed as well, but it takes more work and more skill.
While the 300-second sub picture shows more stars, frankly I think the 60-second x 10 image actually looks better. 60-seconds isn’t long, no, but NGC 6207 is just as visible in the shorter sub-stack. It was also much easier to process with a less bright background and not as much color shift (the background was more on the order of brown than red).
Conclusion? In a light polluted backyard, shorter, more numerous subs are often better, or at least easier to process, than longer subs no matter how many longer subs you take. What your exposure limit should be depends on the degree of light pollution and the current sky conditions.
For me, 300-seconds is a good subframe exposure on a dark(er), dry winter night when I have a zenith limiting magnitude of 5.0 or so. On a spring or summer evening when humidity scatters light pollution, 1 – 2-minute subs are what I do. On this summer’s night, ten 60-second subs were definitely preferable two two 300-second subs. And more 60-second subs would have been better still. So why did I stop with ten? Ah, on that hangs the short tale of this annum’s M13…
|300-seconds and the background is a bright pink-red...|
As July came in, the question became not “When will I get M13?” but “Will I get M13 at all?” There had been precious few opportunities to take deep sky pictures all spring long. And not that many this past winter, either. Summer was thus far shaping up to be as bad if not worse. So, when Accuweather’s Astronomy Forecast on the web and my Scope Nights and Clear Sky Chart apps on the iPhone began to look slightly favorable, I got my rig set up in the backyard tout suite despite temperatures climbing well past 90 (try “feels like 101F”) and high humidity.
Said rig? My SkyWatcher 120ED refractor, Miss Hermione Granger, Celestron AVX GEM, and old Canon 400D. Why was I using the lighter mount rather than the Celestron CGEM? I was a wimp. An astro-wimp. I couldn’t face the prospect of lugging the 40-pound plus CGEM head out into the backyard in the heat.
By the time I finished cabling up everything—camera to computer, mount to computer, guide scope to computer, shutter control cable to camera, dew heater, mount power cord, hand control, etc., etc. etc.—I was wet with sweat and just this side of being overheated. Seeing as how it doesn’t get dark till way past 8:30 in these days of daylight savings time, however, I had sufficient time to cool off before starting the run.
When the stars finally began to wink on, I got the VX polar aligned. As I mentioned some time ago, I no longer use Celestron’s All Star Polar Alignment routine (in the hand control) to do my polar align. I find Sharpcap’s polar alignment tool, which uses the guide scope and guide camera is easier and more effective. My declination error with a Sharpcap polar alignment is noticeably lower than it ever was with ASPA, even given two ASPA iterations.
|60x10 (top) and 300 x 2 (bottom)...|
When I was satisfied with my composition, I switched to PHD2 and got its guiding calibration out of the way, clicking on a bright, but not too bright field star. PHD2 calibrated readily, and when that was done began guiding. I always give the auto-guiding a few minutes to settle down, and, so, walked back inside to enjoy the cool for a few minutes. Returning outside, looking at PHD2 revealed the RMS guiding was about 1.5” or lower, more than good enough for my 900mm focal length refractor and APS-C size chip. That being the case, I returned to Nebulosity, and instructed it to take 25 60-second exposures.
A great thing about Nebulosity and PHD2? They are rock solid. If I wanted, I could have just sat inside and let them do their thing without me. I got bored with channel surfing however, and returned to the laptop on the deck before long. PHD2 was guiding great, and the frames coming up on Nebulosity looked good. I noted little NGC 6207 immediately. All was well. Until...
Just as I began to wonder whether I should go back to the den and see if there were something good on Netflix, my iPhone just about gave me a heart attack with its alert tone. The issue? “A line of severe thunderstorms is headed your way.” Rut-roh, Raggy! Looking to the west, I realized that what I’d thought was distant fireworks was actually lightning.
Hmmm. Should I wait and see? I’d only accumulated ten subframes so far. Unfortunately, the phone insisted the weather would arrive by 11:45, and it was already past 11:30. Deciding discretion was the better part of valor, I turned off the AVX, covered Hermione and the mount with my Telegizmos cover (recommended), disconnected the computer, and scurried inside.
I was a little miffed, but back in the blessedly cool den, I realized that out in the heat and humidity I had begun to get dehydrated without realizing it, so mesmerized by PHD2’s tracking graph I had been. I re-hydrated with a Gatorade and called it a night. I was tired enough that I didn’t even deign to look at the year’s M13 on the laptop.
|My yearly M13 2017...|
Next morning, I stacked and processed my shots—which I thought were pretty pleasing and far from the worst annual M13 I’ve ever done—and strategized about the coming night. The storm had come and the storm had gone, so I would be able to get out for a second summer night in a row (!) it seemed.
What would I do? I had two things to accomplish. First, I wanted to take some longer subs of M13, 300-second subs, for the comparison above. I also wanted to do a little experimenting with the PEC function on the AVX, something I had not previously gotten around to despite having owned the mount for four freaking years.
And so, I hit the backyard once again. My experience with PEC and long(er) subs on the AVX? That, my friends, is a subject for next week.
Sunday, June 11, 2017
Issue #542: The Curious Case of the Schmidt Cassegrain Telescope
In the last few years, however, I’ve made it no secret that I’ve somewhat turned away from SCTs and to refractors for a variety of reasons. What gives? Am I now fer ‘em or agin’ ‘em? Answer? It’s complicated.
In fact, just about everything concerning the SCT is complicated except for its relatively simple design (other than that dratted corrector). Moreso than any other telescope it raises strong emotions. It doesn’t just have fans and skeptics, it has lovers and enemies. It’s unusual to see a general discussion of the SCT online on BBSes like Cloudy Nights that doesn’t degenerate into slings and arrows from both sides.
That being so, I thought this Sunday we’d go over the arguments of both the prosecution and defense in the Curious Case of the SCT: Is it a Good Telescope or Not?
For the Defense:
The SCT is Portable
The Schmidt Cassegrain is just naturally easy to transport and set up given its folded optics and short tube. The C8 packs two meters of focal length into an OTA less than two feet long. Carrying around and mounting an 8-inch f/10 Newtonian is something of a nightmare, but an 8-inch f/10 SCT is practically a grab ‘n go scope, to summon that overused cliché.
A modern fork mount model is virtually a self-contained observatory. Not only is there goto, computerized pointing, to the tune of tens of thousands of objects, some models now feature built in auto-guiding, wi-fi, and can align themselves with little user intervention. An 8-inch SCT, a battery, maybe a DSLR, a box of eyepieces and you are ready for either visual or imaging work at the drop of a hat.
These Telescopes are Supremely Affordable
The most amazing thing about SCTs? They’ve gotten cheaper. Back in the day, in 1995, I paid over two-thousand dollars for my Ultima 8 SCT. It was a nice enough telescope with very good—if not perfect—optics and a sturdy fork mount and tripod. However, there was no goto or other computerization. The mount was powered by a 9-volt battery. Turn it on and the telescope tracked, turn it off and it stopped. It did have a Periodic Error Correction (PEC) feature, but when you turned the scope off at the end of the night, your hard-won PEC “recording” was lost and you had to re-do PEC all over again the next evening. Otherwise? There wasn’t even an auto-guide port.
|Me and my new Ultima 8 circa 1995...|
Today, 1500 bucks in our decidedly smaller dollars will get you a Meade LX90, a very competent SCT with a sturdy-enough mount and tripod and a hand control with zillions of objects. If you can bump the budget up to 2700 George Washingtons, you can have an LX200 GPS, a telescope that doesn’t just include just about every conceivable computer feature, but which has a mount at least comparable to that of my old Ultima’s massive fork. Oh, and the LX has a much better-looking field edge than the Ultima 8’s thanks to the telescope’s ACF, “Advanced Coma Free” optics. While I haven’t done the computation, the LX200’s current price is still likely less in real dollars than what I paid for that manual telescope in '95.
Meade and Celestron’s Optics are Excellent Now
I’m not just talking about the dreaded Halley-scopes, the SCTs produced during the comet Halley craze, when I say Schmidt Cassegrain optics could be variable in the past. There were some excellent ones, but there were also some dogs. The good news is that both companies are very consistent today. There may be fewer stand-out scopes, but there are also far fewer poor ones. Add to that advances like Celestron’s Edge optics which reduce coma and field curvature, and Meade’s ACF optics, which reduce coma (and which are available in f/8), and it’s no exaggeration to say that in general terms SCT optics are better than they ever were.
The SCT is Well-suited for a Variety of Tasks
Thanks to features like the moving mirror focusing system dreamt up by the man who invented the commercial SCT in the 1960s, Celestron’s founder Tom Johnson, few telescopes are so suited to such a wide variety of tasks. You can take high resolution pictures of Jupiter one night, observe deep sky objects the next, and do spectroscopy of distant galaxies the evening after that.
It’s not just that the moving mirror focusing gives the SCT tremendous a back focus range that will accommodate eyepieces, cameras, and other sensors of all types, it’s that it has become the PC or telescopes. The SCT has been around in commercial form for over 50 years, and both companies have more or less retained the standards Celestron implemented in the 70s. A visual back from the mid-1980s will still screw on to any modern Meade or Celestron SCT. That means there’s a huge number of accessories and add-ons for these scopes.
Those many accessories include focal reducers and extenders (Barlows), and thanks to the Schmidt Cassegrain’s focus range, it’s easy to make these things work on the telescope for visual or imaging use. Most SCTs are natively f/10 telescopes, but just a few dollars gets you extenders and reducers that give you an f/20 and an f/6.3 too. It’s like having three telescopes for the price of one.
The Schmidt CAT is Usually on the Cutting Edge of Technology
When some new innovation is developed, it’s usually developed for SCTs first. When goto came to commercial amateur scopes, it came in the form of the Celestron Compustar and Meade LX200 SCTs first. If you want the latest and the greatest—like Meade’s Starlock System, which provides integrated guiding and goto—look for it in Schmidt Cassegrains and especially fork-mount SCTs first. Why? In part because Meade and Celestron SCTs are still the most popular commercial telescope. The numbers keep the prices down despite ever increasing (electronic) features. An impetus to this innovation is the fact that you’ve got two companies competing for one small market. It’s like Honda and Toyota—the two keep innovating and adding more features in hopes of pulling ahead of the competition.
|High-tech observing in the 90s...|
For the Prosecution…
The Schmidt Cassegrain May be Transportable, but it isn’t always Portable
Certainly, smaller SCTs are quite portable, but not quite as portable as they’re often said to be. If you don’t mind carrying a telescope out in at least two pieces and assembling it, a 5 to 8-inch SCT is portable. However, even A C5 stretches the idea of grab ‘n go. Oh, some people might pick one up in one piece and waltz it into the backyard, but it’s more of a handful than you’d think. Most Fork mount C8s? Few of us would want to carry one more than a few feet. A fully assembled C8 on a GEM, even on one of the relatively light CG5/VX/Exos size mounts? No way, not unless you are the incredible Hulk.
Get above 8-inches, especially with fork mount models, and even “transportable” becomes dicey. A 10 – 12-inch fork SCT OTA/fork/drivebase will weigh in at around 50 to 70 pounds. Even when setting up in alt-azimuth mode, more than a few people will be challenged. You’ll have to lift that awkward tube/fork/drivebase combo onto a tripod at least waist high and get it oriented on and bolted to said tripod. Onto a wedge’s tilt-plate for use in equatorial mode? At the 10-inch level that is sometimes a job for two, and at 11 and 12-inches it most assuredly is. The biggest CATs, the 14s and 16s, are telescopes for permanent or semi-permanent installations where you can at least wheel scope out of storage and onto an observing pad.
How about a GEM, then? A 10-inch isn’t bad. At 11-inches, however, many normal adults will be stressed. It’s not so much the weight as it is the awkward bulk that has to be held steady as the dovetail is slid into or tipped into the mount’s saddle. A 12-inch is entering the realm of scary for most, and a 14-inch—which is like wrestling with a full garbage can—is a daunting task. Mounting a 16-inch is a serious undertaking for at least two men.
SCTs in smaller sizes are transportable and convenient, but as aperture increases, they become surprisingly less portable than some other designs. Today there are 20-inch (ultra-light) Dobsonians that are far more portable than a 12-inch LX200.
These Telescopes are Affordable, but You Do Get What You Pay for
There is no denying Meade and Celestron Schmidt Cassegrains are supremely affordable considering their apertures and features, but there is a reason they are cheap. While both companies have thousands of satisfied customers, the road to satisfaction is sometimes a rocky one. One of the reasons SCTs are inexpensive is that they are made and sold in (relatively) large numbers. Another, more concerning, reason is the Chinese companies’ QA programs are not exactly robust. Even scarier is that some of the materials and parts used in these telescopes are of lower quality than they should be.
|Me and the bigun...|
A case in point was Meade’s much heralded RCX400. The one I used (loaned me by a Meade rep at a star party) worked well and had some amazing features. I did note the fit and finish was rather poor even for a mass produced SCT, especially given its 4000 dollar plus price tag. Internally, it turned out, the story was even worse. Many of the telescopes arrived DOA, often thanks to the inexpensive motors Meade used in the focusing and collimation system—and that was just the tip of the iceberg.
While the RCX is an extreme example, the same sort of thing, the same low-balling of parts and lax QA, is evident all across Meade's and Celestron’s product lines. Wise advice? Don’t be an early adopter of one of the companies’ scopes. While both do tend to get their products right, it often takes a while—that “while” extending even to “years.” If you get a DOA SCT and have to ship it back to your dealer or the maker, or if your scope develops continuing problems, it may not seem like such a bargain after all.
Meade and Celestron Optics are Pretty Good Now, but are Still a Compromise
Both companies have come a long way since the 1980s and early 1990s when it comes to optical quality. And, certainly, credit where credit is due for them introducing improved designs like the Edge and ACF. However, SCT optics with their 30% range central obstructions will always be a compromise. Their contrast characteristics are never going to be as good as those of unobstructed or minimally obstructed scopes. Also, thanks to their mass-produced nature, these days you will likely get good optics but you will rarely—if ever—get great optics. Surprisingly, both companies produce great refractor optics and often excellent MCT optics. It seems SCTs are just a little more difficult to get to that level, and it appears they always will be.
The Schmidt CAT is a Jack of All Trades, but Master of None
The SCT is indeed good at many things, but there are often other designs that are better at any one of those things. If you are an astro-dilettante like Uncle Rod, that may not matter, but if you have a special interest area in our avocation, it might. A Newtonian or a refractor, for example, is a better instrument for planetary observing. A large and portable Dobsonian is better for visual deep sky work. A refractor, an APO refractor, is arguably a better choice for deep sky astrophotography (although an SCT can certainly shine when it comes to imaging small DSOs or planets).
Sometimes We’d be Better Off Without All the High-Tech Gimmickry
|Even "just" a C11 is a handful...|
That is up to you. I’ll let you make up your minds about it and would love to hear your decisions in the comments section. Me? These days I am perhaps not quite the Schmidt Cassegrain evangelical I once was, but I still use them. My stable may have shrunk to a single C8 (my Edge 800) and a C11 (whose days may be numbered), but, yeah, I still use ‘em.
When I do pull my C8, Emma Peel, out of her case, it’s like coming home. I know, Mr. Wolfe said you can’t go home again, and that is somewhat true. I am more aware of the design’s warts than I used to be (or would admit), but I still believe “right tool for the right job,” and that right tool is still sometimes the good old Schmidt Cassegrain.
When I do pull my C8, Emma Peel, out of her case, it’s like coming home. I know, Mr. Wolfe said you can’t go home again, and that is somewhat true. I am more aware of the design’s warts than I used to be (or would admit), but I still believe “right tool for the right job,” and that right tool is still sometimes the good old Schmidt Cassegrain.
Sunday, May 28, 2017
Issue #541: Taking Pictures with a C8
When I’m speaking about the history of Schmidt Cassegrains at star parties, club meetings, or cons, I often get puzzled looks and questions from new amateurs about one of the things I say: “One of the big reasons for the 8-inch SCTs becoming the most popular commercial telescope in the 70s was astrophotography.” What? Everybody knows SCTs aren’t good for taking long exposure deep sky pictures. For that you need a short focal length refractor, right?
Maybe and maybe not. Firstly, back in the 70s when the Schmidt Cassegrain began its rise to fame, the other common telescope alternatives for deep sky astrophotography were the cumbersome, shaky Newtonians practically everybody owned, and refractors with focal ratios of f/15 or more. Take it from someone who was there, it was a million times easier to take deep sky astrophotos with a C8 than one of those telescopes.
Also, while I won’t disagree that for beginners in astrophotography, a refractor of short focal length is easier to manage in the beginning, we don’t remain beginners forever. Eventually you may discover more focal length, aperture, and resolution than what your 80 – 100mm refractor offers can be a good thing. So what are the problems with using the average Celestron C8 or Meade 8-inch for deep sky imaging?
The first gremlin is simply all that focal length. With a C8, you start out with a native focal length of about 2000mm. That is what, more than anything else, makes long exposures tough with the telescope. At 2000mm, every tracking faux pas your mount commits will be exaggerated. Not as stable as it ought to be? A tiny gust of wind will ruin your picture by creating trailed stars no matter how well you guided. That may make anything but the shortest exposures problematical in autumn and winter when the winds are wont to blow.
Also, if you’re a plebe like me, you won’t be using a 10 thousand dollar mount for your telescope and will have to guide it. You’ll use a small auxiliary camera to keep the telescope precisely centered on the target despite the inevitable back and forth motion of periodic error caused by less than perfect gears. At 2000mm, you will have to guide precisely. How precise depends on the pixel size and sensor chip size of the imaging camera, but you can bet there won’t be much room for error.
Then there are the mirror flop blues. To focus, the primary mirror of a Celestron or Meade SCT slides up and down on the baffle tube that protrudes from the main mirror. The mechanical tolerances there are OK for visual use, but are loose enough that the mirror can move slightly when the attitude of the telescope changes significantly—as when crossing the Meridian. Result? Those darned trailed stars if you’re using a separate guide telescope for auto-guiding the mount. To the guide camera, everything looked fine, but the image moved in the main camera when the mirror flopped.
|An imaging rig back in the day!|
None of these things present insuperable difficulties, though. After all, me and my mates were using C8s to take good pictures—which I define as pictures that made us happy—thirty and forty years ago. We didn’t have electronic cameras, either. We manually guided our telescopes and usually exposed for a minimum of half an hour even on bright objects and with “fast” film in our SLRs. If we could get decent shots with a Schmidt Cassegrain then, certainly you can now.
Again, I don’t endorse a C8 or Meade 8 as your first astrographic telescope. Cut your teeth on the vaunted fast ED refractor—they are cheap now and come as close to being foolproof for deep sky imaging as you can get. But when you are ready to move up in focal length and aperture, however, begin collecting the astro-stuff you will need…
Get a Modern SCT
Get an Edge (Celestron) or an ACF (Meade). Their better field edge performance is a good thing, no doubt about that, especially if you also intend to use the scope visually. Admittedly, unless you are employing a camera with a full frame 35mm sensor, you won’t notice the difference in images, but you might as well invest for the future so that if/when you move to a bigger chip you’ll be ready.
The really big deal with modern SCTs for imagers is not necessarily the field edge, but that they have mirror locks. The Celestron Edges have them, and so do the 8-inch Meade ACF telescopes. These locks stabilize the primary mirror and prevent it from flopping if you are guiding with a separate guide scope.
Get a Focal Reducer
All the Meade and Celestron 8-inch SCTs come in at f/10, that 2000mm we talked about above. Not only does that many millimeters make guiding and tracking more difficult, it makes for longer exposures and can be a challenge for accurate goto pointing. The solution? If you get the Celestron, buy the Edge f/7 reducer. If a Meade, the standard Meade f/6.3 reducer corrector (the Celestron 6.3 works fine on Meade scopes too). The Meade and Celestron 6.3 reducers are reducer correctors, designed to flatten the field edge of non-ACF telescopes, but they work just fine with ACFs since most of their effect is to, yes, flatten the field rather than remove coma—which the ACFs’ optical system does itself.
|A 66mm f/7 makes a nice guider...|
How about other focal reducers? Like those from Optek? They can be a good choice if you’ve got a Meade scope, but some can’t be used visually. Those for the Edge scopes definitely can’t. Only the Celestron f/7 Edge reducer can be used for that. Since you’ll probably want to eyeball the heavens your Edge SCT once in a while, get a reducer that will work with an eyepiece.
Get a Good Enough Mount
This is the most important thing if you’re considering SCT astrophotography: how good is the mount’s tracking? Especially with a payload consisting of an 8-inch SCT, camera, and guide scope (which may be upwards of 30 pounds). It doesn’t matter if you image with a fork mount or a German equatorial—both have their pluses—it just matters that you get good tracking with a tricked out 8-inch SCT onboard.
Can you get by with the fork mount that came with your telescope? Maybe, if it’s of fairly recent vintage. Older forks can be a crapshoot. I once encountered a Meade LX200 GPS with 90” of periodic error (that’s a lot). Modern forks like the CPC Deluxe from Celestron and the fancy LX600 from Meade are certainly much better for imaging than the old ones. HOWEVER, thousands of good long exposure images have been taken with the minimalist AC driven fork mounts of the 70s and 80s. Use what you have, but a good mount makes things easier.
For most of us, a good mount is a GEM. A German equatorial has the advantage of allowing you to use a variety of scopes on the mount. You can do widefield with a refractor without the hassle of trying to piggyback it on a fork mount’s SCT OTA. One is also more portable than a fork mount, though an 8-inch fork SCT isn’t too much of a hassle for most of us to transport and set up.
How much should you spend on a mount? That’s up to you. Prices for GEMs usable for imaging with an 8-inch Schmidt Cassegrain range from about 800 dollars all the way up to 10 thousand dollars and more. Before spending oodles of cash, though, ask yourself how often you are really going to be able to or want to take pictures. For most of us that is maybe once or twice a month--IF the weather cooperates.
Me? Thanks to our stormy Gulf Coast, I rarely do astrophotography even once a month. For me, an inexpensive imported GEM is more realistic than a top of the line AP, Bisque, or 10Micron. Keep the sub-frame exposures down to 5-minutes for less and an Atlas or a CGEM can work very well with an 8-inch SCT. Given my usual conditions, it’s not like I’m going to be taking 12-hour exposure sequences anyhow.
Don't scrimp on the mount, though. While I’ve taken OK images with my C8 and a CG5 or AVX GEM, it was clear these mounts were at their limits with the telescope. And so are the other GEMs in this class up to and including the HEQ-5 (Sirius). For ease and reasonable consistency of results, consider the next step up, the EQ-6 (Atlas) or CGEM or CGX mounts. If your skies and your skills are better than mine, and you are less lazy than me, I wouldn’t criticize you for bumping the mount choice up to a Losmandy G11 (about 4K), but you don’t have to do that to shoot good deep sky astrophotos with a C8. An Atlas type mount will do it.
Get a Sufficient Guide Scope
Today’s sensitive, high resolution guide cameras don’t require the crazy long focal length guide-scopes we used in the day of manual guiding. Still, you need a guide scope (a refractor or a reflector that does not use a moving primary mirror to focus) with enough resolution so the guide camera can “see” small errors when imaging with an SCT.
I am lazy and get along with one of those 50mm finder-guide-scopes that are so popular now, but I suggest a minimum of 400mm of focal length for the guide telescope when doing C8 astrophotography. A Short Tube 80 or similar will do as long as you can lock the focuser down securely. And you have a sturdy mounting for the 80. That is incredibly important when imaging at these focal lengths, since the smallest amount of flexure in the guide scope rings will show up as trailed stars in the main scope’s images.
Get an Off-axis Guider
Well, maybe. I suggest you try a guide scope first and only if you find you just cannot get the gremlins out of your guiding setup no matter how you tighten things down or tweak the Brain settings in PHD2, should you consider an off-axis guider.
An “OAG” allows you to both guide and image through the main scope. One contains a little “pickoff” prism that diverts a small amount of the light at the edge of the telescope’s field to the guide camera. Since it is seeing the same images as the main scope, problems like flexure and mirror flop instantly disappear.
Unfortunately, there’s a price to be paid. The OAG will only pick up stars around the periphery of the telescope’s field. There may be few of the them, and their shapes may be distorted if you are using an older “standard” SCT whose field edge is not perfect. In this day of sensitive guide cameras, the problem of finding a suitable guide star is not as bad as it used to be, but it can still be difficult. I used an OAG all through the film days, but never found it to be a pleasant experience.
Get a Good Polar Alignment
Declination drift due to poor polar alignment just makes the task of guiding more difficult. Strive to get within a couple of minutes of the celestial pole if possible. That used to be tough, but innovations like the Polemaster polar alignment camera, and the polar alignment routine in Sharpcap (which uses the guide scope and camera to do the alignment) have made it positively easy.
Tips for Getting it all to Work
|C8 Edge plus Atlas EQ-6: not quite perfect but mine...|
With a sub-Losmandy mount, a Chinese GEM up to and including the iOptrons, be scrupulous about balance. That means balancing the mount so it is slightly east-heavy. Of course, you will likely have to rebalance if you move far from your initial target. That is not a big problem for most of us, since we’ll usually only image one or two objects a night and it’s easy enough to pick two subjects in roughly the same part of the sky. “East heavy” can make a big difference in how an imported mount performs, since it ensures the R.A. gears are always properly engaged.
Keep Subs Short, but…
With a C8 riding on an AVX or similar mount, you may find it to your advantage to keep individual exposures short. To pehaps a minute or two. If you have a bad spot on your gears, just throw out that sub-exposure and be on to the next one. Over an exposure of 5 – 10-minutes, there’s a lot that can go wrong with a light mount’s tracking ruining that whole, long shot.
Do remember, though, that sub-exposures have to be long enough to capture desired detail. While stacking subframes will make a shot less noisy and smoother, no detail not visible in a single sub-frame will show up in the final, stacked, photograph.
Keep Working with PHD Settings
I didn’t for the longest time and am now sorry I didn’t. The settings I had were good enough for the APO refractors I usually use for imaging these days, yielding RMS guide errors of 2” or a bit more on my AVX and CGEM. Couple that with my laissez faire approach to polar alignment, and most of my shots with a C8 (reduced) didn’t have perfectly round stars if I zoomed in enough in Photoshop or whatever.
Eventually, I decided I needed to do something about my guiding, since I wanted to begin imaging with the Edge C8 again once in a while. I read up on the PHD2 Brain settings and devoted one entire evening to tinkering with them. In just that one night my RMS guide errors went from 2” to 3” to a bit more than 1” at best, and under 2” at worst. That, coupled with Sharpcap polar alignment, has meant that for me imaging with the C8 is easier than it ever has been.
Shoot Appropriate Targets
If a target, a medium-small galaxy or globular cluster, perhaps, cries out of an 8-inch SCT, by all means use one as the imaging scope. If it doesn’t? Use a nice 3 – 4 – 5-inch ED refractor instead. Why make things hard on yourself for no good reason? In addition to less focal length, a refractor in this range will be lighter than the SCT, and an inexpensive GEM mount will always track better with a lighter load.
And that is that. Don’t be afraid to try long exposure deep sky astrophotography with an 8-inch SCT, no matter what you may have read on the darned Cloudy Nights BBS. A little experience and you may find it’s not as difficult as you'd been led to assume, and that the focal length and aperture of your friendly, neighborhood C8 or M8 brings a new dimension to your astrophotography.
Sunday, May 07, 2017
Issue 540: Get Thee to a Dark Site II
Last ish we got you a dark site, or at least gave a few pointers as to how you and your fellow astronomy club members could find and keep one. This time, we’re going to talk about using that site.
And you know you want to use it. Sure, in this day of electronic cameras and computer processing you can take pretty good pictures from the backyard, but you’ll always get better results under dark skies. Visual observer? As I said last week, the galaxies of spring cry out for the darkest skies possible.
There is no doubt about one thing, spring weather in the USA, and especially east of the Mississippi, can be capricious. Before talking about what you bring to your club’s observing field and what you do there, maybe we should discuss “whether.”
Obviously, if you’ve got beautiful blue skies and the forecast is for more, a dark site trip is a natural. But what if the sky is unsettled and the weather forecasts ambiguous? Back in the day, back when I was more sanguine about hard-core observing, back when I lived downtown and couldn’t observe anything from my backyard, I had a rule, “If it ain’t raining, head to the dark site.”
That stood me in good stead for years, and resulted in me seeing far more than I would have if I’d let a few clouds scare me off. Most of the time—though certainly not all of the time—I at least saw something at the club site in return for an hour’s journey into the west. I would sometimes wimp-out observing plan and gear-wise, though. If the sky really did look doubtful, I’d tend to change my plans from “astrophotography” to “visual,” and the telescope from my C11 to my 5-inch ETX Maksutov Cassegrain, Charity Hope Valentine. Anyway, I always found that even if I was mostly skunked, I had a better out on the observing field than I would have had sitting at home watching television.
Let’s say, you’ve got a night that looks to be uncompromisingly good, though. What do you load into your vehicle? The simple answer is “everything you need, nothing you don’t.” Certainly you want all the gear you require to allow you to execute whatever your observing plan is, but there are things you’d take to a multi-night star party that you will likely want to leave at home for a club site run. Remember, you’re going to have to pack all that stuff back into your car at the end of the evening and possibly unload it at home.
What NOT to Bring to a Dark Site…
You may actually need an observing table depending on your vehicle and what you are doing, but maybe you can back off from a big camp table to a TV tray. If I am doing visual observing, a table just large enough for an eyepiece box and maybe a star atlas is more than enough. Imaging? I’ll need something to put the laptop computer on, but not anything more than that.
When I switched vehicles from a sedan (a Camry) to a truck/SUV (4Runner), I eliminated observing tables altogether, operating out of the back of the 4Runner, tailgating it as it were, which is the best of all worlds—I even have AC power available there from the truck’s built in inverter and auxiliary battery.
This is a maybe/maybe not thing. Even if you are doing imaging, you may be able to eliminate the laptop. Using a standalone auto-guider and a digital single lens reflex (saving images on the camera’s memory card) can allow that. By saying “ixnay” to the laptop, you can also leave one large battery at home (a laptop’s internal battery will rarely last an entire observing run), the above mentioned table, cables, mouse, mousepad, etc., etc., etc. Yes, it’s nice to have a computerized star atlas like Stellarium, but in the interests of simplicity, sometimes I don’t mind getting reacquainted with Sky Atlas 2000 or Uranometria. Just can't go back to that? SkySafari running on a tablet is a good compromise.
Stuff you always bring and never use
You tend to throw a pair of binoculars in the car, but never/rarely use them? Leave them at home. The same goes for stuff like extra flashlights, a second box of eyepieces, radios, ice-chests, etc. All that junk is nice at a big star party, but you are not going to be at the dark site long enough to feel the need for this stuff.
A telescope that is just too much
|Small can be beautiful...|
We all want to maximize our observing experience, but if a telescope is so large and/or complex, that by the time you get it assembled and working it’s time to go home, leave it at home. Give me a freaking C8 for dark site use not a C11 or (horrors) C14. When all your buddies are packed up and ready to hit the road and you still don’t have the scope off its mount, I think you’ll begin to believe that sacrificing some aperture and/or features might not be such a bad idea.
Things that will annoy your fellow observers and possibly the landowner
Radios blasting your particular preference in music and green laser pointers that make the sky look like something out of Return of the Jedi have no more place at the club dark site than they do at a big, organized star party.
What to Bring
Sure, you know to pack the telescope, but make sure you pack all of it. One night, one cloudy night, when it wasn’t raining, nevertheless, I headed to the dark site with my C11. As soon as I arrived onsite, almost magically the clouds began to scurry off and I began assembling my big scope. Yes, as above, it was really too much for a short dark site run, but I was younger, stronger, and dumber then.
I had just got the NexStar 11 GPS on her tripod when I had a vision. Of the telescope’s hand control sitting on the dining room table of Chaos Manor South. And that was just where I’d left it. What to do? There wasn’t anything to do. I packed up and went home. I was just thankful I wasn’t at a star party 400 miles away.
In the interests of this sort of thing not happening to you, it’s a good idea to have a checklist. If you know an item is necessary, put it on the list and don’t check it off till it is packed in the car.
|A telescope that doesn't need batteries can be nice sometimes...|
Some lucky folks have AC power available at the club site, but that is rare. Be prepared to operate off batteries all night. So, ensure your batteries are fully charged beforehand. Don’t just assume they are. What sort of batteries? I favor the ubiquitous 17ah jump start battery packs. Not only do they have enough juice to power most scopes and accessories all night, they usually have built in lights which are handy when you are packing up at the end of the evening. Yes, don’t take too much stuff, but don’t scrimp on batteries. I always take one for the (goto) scope, one for the dew heaters, and one for the laptop.
At home, in my backyard, I can often get by without a dew heater system on my SCTs and refractors. My house and neighboring houses and trees shield much of the heat sucking sky from the view of my scope, acting as giant dew shields. On an open field out in the country? Uh-uh. Even if your area is drier than my Gulf Coast stomping grounds, you’ll need something to keep dew off.
Dew prevention is a subject for an entire article, but I can offer some basic guidance here: use heater strips on objective or corrector. If all you have is a dew-zapper gun—a 12 vdc hair drier cum window defroster—you will soon lose the battle against dew. A zapper can be sufficient for the secondary mirror of a Newtonian reflector, however.
You’d think this would be something I’d tell you to leave at home, but it isn’t. Even for a relatively short visual observing run, being comfortable means you will see a lot more. Bring the chair along.
Use that checklist to make sure you bring the vitals: eyepieces, star diagonals, star charts (or a smart phone or tablet), red flashlights, etc. Don’t overdo. I restrict myself to one eyepiece case and one accessory box (a large Plano tacklebox).
|"If it ain't raining." Sometimes you eat the bear, and sometimes...|
Whether “just” a can of Deep Woods Off, or a Thermacell, don’t even think about heading to the dark site without bug zappers except in the very depths of winter.
“But Uncle Rod, it’s only gonna get down to the lower 70s.” Bring a coat or sweater or sweatshirt anyway. You will never be colder than when standing nearly stock still at a telescope under an open sky. Let it get to the mid-60s and you will begin to shiver and will throw in the towel unless you are prepared.
Don’t just always bring your cell phone with you as we insisted last time, make sure it is fully charged before leaving home. Taking a DC charger to the site might not be a bad idea either.
A Few Amenities
You won’t be out there that long, so don’t pack too much additional stuff, but certainly a few bottles of water and maybe even a couple of snack items is “reasonable.”
It’s your dark site, set up anywhere you like, right? Sure. But some places are better than others. If there’s been a recent rain, you’ll be better off on your field's high ground if it has any. You probably don’t want to be on a slope, however; telescopes are happiest on level ground. One other thing? Togetherness is fine. You want to be close to your buddies so you can share observations, chat, etc. However, if you’ve only got a few people at the site there’s no need to set up 3-feet from the next scope. Spread out and give each other some room.
You observe the way your normally observe at home or at a star party. What I’m really talking about here is observing rules. Your club probably needs to come up with a few. You want to prohibit white light and probably green lasers. But you don’t want to keep adding so many rules that people feel stifled. And be aware that at a club site with two or three people on the field, all those beloved rules formulated at that marathon club business meeting are likely gonna be observed in casual fashion at best.
For example? You wouldn’t dare fire up your vehicle and drive off a star party field at midnight, but at the old dark site with a few people around? It’s likely to be, “Had a great night Wilbur! See you next time, Hiram! Gotta head on home.” If everybody’s observing visually they can shield their eyes while you motor off. If someone’s in the middle of an astrographic exposure, wait until they are done. Just use common sense—and the same goes regarding any rules you and your mates think up.
The Moon is rising, or it’s just late, or it’s just you and your friends’ usual turns-into-a-pumpkin time. What about tear-down of the equipment? If, as above, you have to leave earlier than your pals, you’ll need to pack by red light (one of those red LED head-lights on a head-band is good if you keep it pointed at the ground).
|You'll soon tire of using a dew-zapper gun...|
Anyway, when the time comes, disassemble your scope, taking care that everything gets back into the vehicle. I tend to be a little less than scrupulous about putting every widget back in its proper place in the cases; I just shovel it all into the car so as not to delay my friends, and worry about sorting everything out the next morning (I can leave all my stuff in my car overnight thanks to a safe and secure neighborhood).
Once everything is back in the car, go over your area carefully with a white light to make sure nothing got dropped and that you’re not leaving any trash behind. Help your fellows out with the same thing. Then—well, you’re off for home (or perhaps your favorite late night bar out in the boondocks).
You’re off if everybody is ready to go, that is. One rule our club has made and that we observe scrupulously is, “Nobody leaves till everybody leaves.” Obviously that doesn’t apply to someone who has to go early for whatever reason. It just means those of us left at the end of the night linger on till the last person has their gear packed. That’s good for security’s sake, but even if, like us, you have a very safe dark site it’s still a good rule to live by. What if the last person standing has trouble getting their vehicle started?
Then, just say your goodbyes, “Great time, y’all! See you next time.” If you did everything right, and your club has the “right” site, believe me, you’ll hardly be able to wait for next time.
Sunday, April 30, 2017
Issue #539: Get Thee to the Dark Site Part I
Spring is here, and with it maybe some clear skies that will encourage you to get out to your club or personal dark site (we’ve had very little rain here, but almost constant clouds). Yes, I constantly preach the worth of the good, old backyard as a spot for deep sky observing, but this is spring, and spring cries out for dark skies.
While some of the bright objects of winter are still on display, if you’re like me you’re focused on the “new” stuff now, the spring wonders on the rise. And what is spring all about deep-sky-wise? Galaxies. The mind-blowing Realm of the Galaxies that stretches from northernmost Coma through southernmost Virgo is back.
Alas, no variety of deep sky object is more harmed by the average suburban sky's light pollution than galaxies . Yes, diffuse nebulae can be tough from the backyard too, but at least a light pollution filter can help some with them. Unfortunately, there is no such thing as a “galaxy filter,” though a few rascals have sold mild LPR filters labeled as such a time of two over the years. The only way to see the marvels of spring as they should be seen is to get to a dark(er) site.
“Dark site? What dark site?” How do you find one if you don’t have one? Lots of factors can influence that process. Are you a club member or a lone wolf astronomer? Are you out in the semi-hinterlands where better skies are a short distance from your domicile, or are you stuck in an urban megalopolis? I can give you at least one unvarying piece of advice to begin, however: if you are indeed a lone wolf, join a club. It’s much easier to secure a dark observing location as a group.
“But I’m not really a joiner, Uncle Rod.” That can be fine if you’ve got a close friend with a piece of land out in the dark and that friend is amenable to letting you use it for observing on a regular basis. If you don’t know anybody like that, though, watcha gonna do?
Forget parks, state and national. Most will insist you buy a camping permit and stay overnight if you intend to be onsite past dusk. Even if you are amenable to that (not me; 3 a.m. is my absolute witching hour), few parks have anything that will serve as an observing field. If there is a suitable open space—and there won’t always be one—it will likely be festooned with streetlights. That’s just the way it is—east of the Mississippi anyhow.
As a member of a club, the possibilities increase exponentially. Even if the club you join doesn’t already have a dark observing location—and it likely will—there will be enough people, even in a smaller club, to guarantee a much larger circle possibilities, a larger group of friends and friends of friends with property out in the dark.
If you get down to “friend of a friend of a friend,” in a dark site quest, you’re much more likely to receive permission to use the property if you approach the person as an organized group rather than an individual (“What kind of a nut are you wanting to come on my land at night?”). And a doubtful land owner can sometimes be swayed with the promise of a modest yearly or monthly check from the club.
Let’s say your club doesn’t currently have a dark site, but sure does want one. What sort of spot do you look for? If you’re bereft of anything but the backyard, any dark location will seem like heaven, but, nevertheless, some places are better than others…
If a site is farther than about 60-miles from the club’s home base, it won’t get used much. As you may have heard tell, it’s often hard to get club members out for observing anyway. My invariable experience is that you can expect maybe 5% of the membership to show up on any given dark of the Moon weekend.
Place your site farther from home than those 60-miles and a maximum 1.5 – 2-hr drive and you probably won't even get the five percenters. You’ll find yourself alone most nights, and you’ll probably stop going frequently yourself after some of the initial fun wears off. 60-miles, however, can work, and is about the distance you need to get from medium-sized and larger cities before sky conditions begin to improve dramatically. See this light pollution map for guidance on how far you need to drive from your particular town (and which direction you need to drive in) for good observing.
If you live in a city that’s got a population of less than 250,000 or so, you can fudge on the 60-miles. My own site is about 30-miles to the west of Mobile, Alabama. Yes, there’s a significant light dome to the east, but that short drive ensures our site gets used frequently. There’s often no more than 2 – 3 observers on site on a clear night, but there is always at least that many folks on the field on any nice evening.
Yeah, I know you often can’t afford to be too choosy, but if there are alternatives there are some things it is best to avoid, starting with bad access roads. Yes, the site is nice and dark, but if getting to it requires traversing a rutted dirt track best suited for 4-wheel drive vehicles, and which is a swamp for weeks after a rainstorm, pass the place by if at all possible. Likewise eliminate a site where any part of the drive is difficult, not just to include the final access road. Paved highways leading to the site and gas-stations and/or convenience stores along the route are a practical must.
Before settling on a dark site choice, a few final checks are mandatory. First of all, get out there with a group from the club (whether your dark site committee or just an interested group of observers) and give the place a try. Try to hit the field on an average, not outstanding, night to get an idea what you should expect most of the time. What to look for? What’s the zenith limiting magnitude? Can you see all the stars of the little dipper (if you can, this will likely be a profitable location). Are there any light domes in addition to the one in the direction of the city? If so, is there still enough good sky for productive observing?
How about the field itself? Is it cut regularly? Can it be? This is very important. The site might be OK in the winter, but in the summer with grass three feet high, what are you going to do? Forget leveling your tripod; how are you going to avoid stepping on Mr. Snake? If the property’s owner doesn’t cut it, you’ll either need to induce him to do so with a financial donation or arrange to get it done yourselves if you are leasing the site, either formally or informally.
Are there any/many ambient lights? You may be surprised at how many land owners have multiple security lights. Frankly, due to the growth of the meth trade, the country ain’t what the country used to be. How many lights are there? Can you live with them? If not—especially if you are formally leasing the land—look into providing the offending lights with full cut-off fixtures (with the permission of the owner, of course).
Finally, how are the bugs? Almost any open field anywhere is going to have some bugs at sundown spring – fall. But are the skeeters, midges, no-see-ums, and blackflies worse than normal and can they be dealt with with Off and/or a Thermacell? Often, really bad bug problems can be traced to a nearby farm pond. Before seriously considering a site, check Google Earth to see if there is a stagnant body of water nearby.
We’re conditioned to think “country safe, city scary.” In recent times, however, thanks to the above-mentioned drug explosion in the country, there has been a reversal. There are certainly some unsavory goings-on out in the boondocks these days. How do you pick a safe dark site?
The worst scenario is a piece of land in full view of a frequently traveled road with ungated access and no homeowner/farmhouse nearby. Before passing up on a site like this, check to see what the crime scene is like in the area (if there’s a newspaper covering the county, you can get crime reports there). Talking to people familiar with the area can be highly illuminating.
If you have no other choice than a dubious site and think it’s worth the possible risk, go ahead, but I suggest making it a rule that “nobody observes alone.” Actually, that’s a good maxim even at a secure site. If your vehicle decides it doesn’t want to start a two in the morning, you’ll be glad to have a buddy or two to lend a hand.
Which brings us to the eternal question, “Should you go armed?” I carried a handgun with me to the dark site a few times a couple of decades ago when I was observing alone, but gave that up. I found that if I were so worried that I thought I’d need firepower with me, I’d be too nervous to observe anyway. I just couldn't concentrate on what I was seeing in the eyepiece. After a few minutes I'd begin thinking every snapping twig represented the approach of a psycho killer. When that train of thought began, I learned it was time to just throw in the towel. Far better than a weapon, I found? A couple of fellow observers. Even with just one other person with me, the place went from scary to friendly and familiar.
Always bring a cell phone on observing expeditions. Not necessarily because it will be handy in case of trouble with bad guys, but in case somebody has car trouble that can’t be resolved and needs a tow. Or, worse, someone has a medical emergency. A cell is worth ten times its weight in Walther PPKs.
Maintenance of the Site
Often, if you are formally leasing a piece of land you’ll be expected to take care of its upkeep. Not just to include the above-mentioned grass cutting, but care of the access road. Members’ cars put some deep ruts in it during the damp spring season? It will be up to y’all to get them filled in. It’s best to have a standing club “Dark Site Committee” as a vehicle to get things like this taken care of and paid for.
You’re not leasing a piece of land, just using it thanks to the kindness of the owner? Don’t wear out your welcome. Even if you’re not obligated to get those ruts filled in, do it anyway (or get a check to the owner). As for the site itself, make sure than when the group leaves it is as much as possible in the same condition as when you arrived. No trash, no cigarette butts, etc. If the owner’s home is nearby, keep the hee-hawing down in the middle of the night. Yeah, know that meteor was pretty, but don’t holler “GOOD ONE!” at the top of your lungs at two a.m.
Yes, it’s OK to invite a prospective club member to the dark site, but… Make it clear that that is a one-time good deal and that regular access to the club dark site requires a paid membership (and possibly an additional dark site fee to cover site maintenance). If you don’t, the word will eventually get out, and you’ll have people you don’t know and don’t know anything about showing up at your observing field.
Enjoy observing from a safe, secure, and dark location! How do you best do that? That’s a story for next time.