Sunday, February 14, 2010

 

Obsessions


For the second week in a row, this is not what I intended to talk about. I had big plans. Maybe get The Herschel Project cranking again. Give the new version of the Stellarium software a good check ride. Possibly even try Deepsky Imaging with the Stellacam. None of that happened, muchachos, largely because of the weather. Far from encouraging me to chase Herschel IIs with C11 and deep sky video camera, the weather looked bad enough by 4pm last Saturday that I decided that, while I’d still run out to the dark site, the scope that would go with me would “just” be Charity Hope Valentine, my cute li’l ETX-125PE.

Which wouldn’t have been bad. Charity’s optics are first rate, and when conditions aren’t perfect she really don’t give up too much to a C8. She is perfectly capable of running under laptop control, too, so I figgered I’d try the new Stellarium with her. Alas, Charity didn’t even get outa the vee-hickle. Far from “clearing at Sundown” as the weather-goobers had predicted, the clouds just got thicker. When I arrived at our site in the wilds of Tanner-Williams, Alabama, I spent a lonely hour (none of my bubbas was dumb enough to make the trip) watching ever more clouds roll in from the east, and shivering in a knife-sharp wind. I woulda thought that wind would have been the herald of clearing, blowing the nasty gray things out. Nope. It was still cloudy when I arrived back home. It was still cloudy when I got up the next morning.

Since then, the weather has, if anything, got worse. In fact, you may not believe it, but it is SNOWING on good, old Chaos Manor South RIGHT NOW. I reckon that’s what the bright boys call “global warming,” huh? (Put your poison pens away. Even ignernt Unk Rod knows you cain’t judge climate change based on one winter.)

I did do a little messing around indoors with Deepsky Imaging. But I didn’t get very far with it. One of the major attractions of that image processing program (written by the author of the Deepsky planner program) is its ability to grab frames and sequences from Stellacams and Mallincams. I attempted to interface my Stellacam II to the program, but without success. It may be my el-cheapo (eBay) USB frame grabber, or it may just be the elderly video card in my elderly laptop. I’ll try to get things sorted Real Soon and report on this program, though, as it looks like a winner.

So what was there to do but rummage through Cloudy Nights and Astromart and the Yahoo Astrogroups. Which brought to the fore something that’s been on my mind and been bothering me for quite a while. Why do some amateurs spend more time obsessing about what their gear can’t do than what it can? Or what might be better for mo’ money out the door. Even when, to the tune of much gnashing of teeth and rending of garments, a dream scope has finally been decided upon and obtained, the angst don’t stop: “Uncle Rod, I shined a 10,000 candlepower spotlight down the tube and I saw dust on the mirror. Whatever shall I do?”

In other words, y’all worry too cotton pickin’ much. And not just you novices, but those of you who oughta know better. Those of you who should know the truth of a maxim that’s as old as amateur astronomy: “Any telescope is better than none.” Sure, I know it’s hard to get comfortable with that. I had a real hard time with it when I was a youngster who owned a 3-inch Tasco Newtonian, but had to look at full page ads for beautiful Unitron refractors every month at Sky and Telescope time. And kept hearing you weren’t NUTTIN if you didn’t have at least a 6-inch telescope…

Aperture Envy

How much telescope can you get by with? How much do ya “need?” “Need” is a slippery thing. Obviously, if you want to follow in Unk’s footsteps and take-on the Herschel 2500, you need as much aperture, as big a lens or mirror, as you can get. All things being equal, my mantra is, Aperture Always Wins. But all things are not always equal. Your circumstances will dictate how much telescope is appropriate for you. If you live in a third floor walkup, a 20-inch Dobbie is obviously out unless you want to reserve all your observing for occasional trips to a darksite. If you are a penniless grad student, there’s not much point in worrying about 10-inch AP Maks replacing your Celestron C-130 anytime soon. It’s OK to want more, but consider separating “want” from “need,” and enjoying what you have.

So how much telescope is required for having fun in astronomy? You can have one hell of a lot of fun with the very tiniest scopes; especially if your skies are reasonably dark. People go for years with Short Tube 80s, doing remarkable work. Hell, folks discover novas with 50-mm binoculars. There is no denying, of course, that if you live in the typical urban/suburban light pollution, there’s a minimum aperture below which you probably shouldn’t go if you want to have access to lots of deep space targets (though you might be surprised how much I’ve seen from Chaos Manor South’s backyard with my ETX-60).

If you want to keep yourself satisfied for even a little while, you need a little horsepower. How much? Not necessarily 20-inches worth. How much will be bearable for you varies, since, again, not all things are equal. I’ve often said, for example, that if I didn’t have my (4.5-inch) Orion StarBlast and my Burgess 15x70 binoculars, I wouldn’t see much over the course of Possum Swamp summers. The heat, the humidity, the clouds mean I am rarely inclined to drag a big gun into the backyard.

My little RFT and my big binoculars mean I see a fair amount through even the worst stretches of skeeter-infested deep south summer. I’d have certainly missed a lot of nice little comets if it hadn’t been for my grab ‘n go pair. Certainly, a compact 8-inch of some design is better, but a 4-inch is still a powerhouse of a scope. I did the entire Messier with my Palomar Junior 4 ¼-inch from my light polluted yard when I was writing The Urban Astronomer’s Guide. Out in the dark, a small scope can blow the big guns away on certain objects. Seeing the entire Cygnus Loop with my StarBlast under good—but not perfect—skies is a memory I’ll cherish for the rest of my days.

Yeah, you know all that. A 4-inch can show a lot if you use it a lot, yadda-yadda-yadda. But you still want more. That’s the life of an amateur astronomy equipment junkie, and even after all these years I ain’t immune. I am looking longingly even now at Celestron’s CGE Pro 1400 HD and making oblique comments about it to Miss Dorothy (ala’ A Christmas Story’s Red Ryder bb gun). And that is fine. Just don’t get yourself to the point I was at a time or two as a sprout, where you can’t enjoy a 4-inch Palomar Junior because you’re wishing for and mooning over a 6-inch Dynascope. I’ve now been in this biz long enough to recognize the wisdom of Mr. Spock’s words: “After a time, you may find that having is not so pleasing a thing, after all, as wanting. It is not logical, but it is often true.”

You avoid ruining today’s telescope with tomorrow’s not just by using the current scope, but by pushing it to its limits. Most amateurs have not even begun to exploit the instruments they have before they jump to the Next Big Thing. A dedicated observer willing to work and experiment and wait for the best conditions can do amazing things with amazingly small telescopes, things even trusted resources like The Night Sky Observers’ Guide pronounce “impossible.” A rule I’ve at least tried to follow over the last couple of decades is to wring every ounce of performance out of the scope I have before worrying about what’s next. The Herschel 400 is impossible with a 4-inch? Let’s see…

The Fanciness Factor

Amateurs don’t just worry about the size of their scopes, they worry about their pedigrees. “All I’ve got is a 12-inch Orion Dob. If only I had a 12-inch OBSESSION I could really go to town.” There is no doubt more expensive telescopes tend to be easier to use for various reasons. If we are comparing two Dobsonians, for example, the expensive semi-custom jobs will usually display far better movements on both axes, will be possessed of cabinet quality wood work, and will be, in toto, more pleasurable to use.

But that don’t mean your Orion (or Skywatcher or Zhumell) is to be scoffed at. Cheap (Chinese) telescopes have come a long ways, and while their mechanics may not be as fine as those of the more expensive spread, the telescopes still work more than well enough for most of us to have one hell of a lot of fun with ‘em. Besides, after a while, you’ll get used to your Orion and, if you try an Obsession, may find it seems, perhaps, too easy in its motions. Don’t mind doing a little tinkering after the sale? Most telescopes and mounts are very simple affairs at heart and not overly difficult to improve. What do you hear if you keep an ear to the ground? That some of the most legendary and expensive scopes may also require some modification before they live up to their press.

Do be cautious about tinkering, though. Like I always say, “The Only Enemy of Good Enough is More Better.” Replacing a Nylon bearing pad with a Teflon one on a simple Dob is one thing. Tearing into your go-to fork or GEM because something you read on the cotton-pickin’ Internet says you might be able to improve it is another. One young man of my acquaintance, for example, took a brand new 12-inch LX200 GPS from being a perfectly respectably performing instrument to a wreck in just weeks.

The telescope worked just fine as delivered, yeah, but what he’d read on the online astro forums convinced him he might be able to improve periodic error just a bit, or improve go-to just a bit, or improve the mount’s steadiness just a bit. What he would up with was a boxful of junk parts. Unless you are experienced and skilled and have the tools and facility for doing such messing around, LEAVE YOUR SCOPE ALONE. If it is doing what it’s supposed to do, forget the stuff on the I-net and just enjoy the sky. NO telescope is absolutely perfect or ever will be. If your instrument is clearly malfunctioning, call the manufacturer or dealer. If it’s not, LEAVE YOUR SCOPE ALONE.

Optical Quality

Yes, the Obsession Dobsonian mentioned above, with its beautiful premium mirror, might present slightly, and I do mean slightly, better images than a prole Orion, but that difference will be small. Frankly, it’ll be too small for most beginners to notice. 99% of the time, those who consider themselves “Advanced Amateurs” won’t be able to tell the difference, either. One other dirty little secret? As aperture goes up, the quality of a mirror’s figure becomes less important. When you get to 20-inches and above, seeing will rarely—if ever—allow that super primary’s (kaff-kaff) supposed 1/20th wave figure to make a difference.

I ain’t telling you to forego an Obsession (or a Starmaster or a Starstructure or an AP or a Tak or any other high-priced scope). One can be a fine instrument, and for those who can afford one, I say “Go for it.” I am just saying that if you cannot or choose not to afford a scope of such caliber, do not despair. What you can see in your humble Skywatcher 12-inch will be very similar—nay, pretty much identical—to what you will see in a 12-inch Obsession or any other similar 12-inch Newtonian. Don’t waste dark sky time pinin’ for the better. The better will come your way one day if you stick with us. For now, just get out and enjoy our wonderful avocation.

Optical Cleaning Compulsion

Amateur obsessions don’t end with obsessing about big Obsessions. One other thing I see a lot on the computer BBS bulletin boards (yeah, that’s what I still call ‘em) concerns optical cleanliness. This obsession is mostly confined to the novices. Those of us who have been in the game for more than a year or two are mostly aware that a speck of dust or three on the mirror (or objective or corrector plate) ain’t gonna do a damned thing to harm images. Think about it: for a change in brightness level to be detectable by the human eye/brain, that change must be on the order of 10%. A speck of dust, or a hundred specks of dust, ain’t gonna be able to do that. Same goes for contrast degradation. Your optical surface will pretty much look like a mass of scratches and sleeks before you notice a difference.

Beginners, unfortunately, don’t know the above—or can’t seem to believe it. They encounter some dust motes in the course of admiring their telescope indoors, PANIC, and begin asking the folks on Cloudy Nights about cleaning. Granted, the way most beginners examine their optics does make them look terrible, even frightening. They use The Flashlight Test. They view the optics under bright and usually oblique light. Which, seems right to ‘em: you always use a bright light when doing critical work, doncha? That might be true when you are looking for your Aunt Lulu’s lost contact lens, but not when examining optics.

You see, The Flashlight Test will make any optics, lenses or mirrors, no matter how clean and perfect, look absolutely horrible. No optical surface is perfectly smooth at the microscopic level. There is plenty of roughness there to scatter the uber-short wavelengths of visible light. That light is scattered across the surface, and dust and small imperfections stand out in stark relief. The result is that the novice freaks.

If all The Flashlight Test resulted in was novices wasting time cleaning their already clean mirrors, it would be funny. But it ain’t funny. Every time you clean an optical surface, even a fairly robust one like an SCT or Mak corrector or refractor objective, you run the risk of doing more harm than good. What profitith it an amateur to clean a dust speck off her mirror if’n she leaves a big scratch behind?

Mirrors can be cleaned with relative safety, but why run the risk when it’s not necessary? If in doubt as to whether optics are “dirty enough,” ask a local veteran amateur to run an eye over ‘em. The classic story about unneeded cleaning? One I got from Doc Clay (Sherrod). You’d have to hear him tell it to get the full frightening (if, I must admit, also a little funny) effect. It begins with a speck of dust on the primary of a brand spankin’ new Meade LX200 and winds up with the telescope in a bathtub full of water (!). My last word on the subject is that it would do a lot of new amateurs a lot of good to see how dirty professional scope optics are allowed to get before they are cleaned.

Secondary Obstruction Blues

This one comes from all and sundry. Even from the refractor troops who don’t got secondary obstructions (maybe it’s Displacement due to the Aperture Envy many of ‘em suffer). If you don’t own a refractor it’s (almost) assured your telescope will contain a secondary mirror suspended in front of the primary one. And there’s the rub. Obviously, that mirror will block some incoming light, reducing image brightness. It will also reduce contrast due to diffraction effects. That’s the jumping off point for many folks’ secondary obsessions which, unlike Aperture Envy, have to do with TOO BIG rather than TOO SMALL.

What’s the ground truth? There is some reality to these worries. A secondary mirror will reduce light throughput somewhat. But only somewhat. Take, for example, the case of an 8-inch SCT with a 3-inch secondary mirror. That’s a large secondary, on the upper end of what you see in scopes at least partially intended for visual use; it has to be for a number of reasons. The effect on light gathering? The 3-inch secondary means the optical system delivers 14% less light than an 8-inch refractor. Noticeable, but only just. And that is compared to an unobstructed 8-inch telescope, not a common or cheap item (in the form of either a refractor or an unobstructed reflector design). It just kills me that folks think they are improving their Newtonians by downsizing their secondaries to the point where they might just as well be using a smaller scope.

What do I often hear at clubs or on the ‘Net regardin’ secondary obstruction? The voice of DOOM. Some Authority proclaims, “A 6-inch telescope with a 2-inch secondary mirror has the light gathering power of a 4-inch refractor.” Not true. Area, which determines light gathering, is being confusticated with diameter. The diameter of a secondary mirror does come into play, but that’s when we’re talking contrast loss. The percentage of the obstruction by diameter is supposed to determine contrast characteristics of an obstructed system. I say “supposed to” because I rarely detect huge differences in contrast due to secondary size until the secondary becomes obscenely large (as in a Richey Chrétien). Truth is, when you put a secondary of any size in the light path, most of the damage is done.

It’s maybe not public knowledge, though I don’t try to hide it, but I own a couple of nice APO refractors. They ain’t exactly top-of-the-line, but they work very well for what I use ‘em for, and I love them. I just want to put the kibosh on the idea many beginners pick up and sometimes revisit when they ain’t beginners no more, that refractors are the magic bullet. Yes, they have advantages, but they are not the cure. Maybe you gain some contrast, but you lose a lot of aperture dollar-for-dollar. That may be acceptable for what you want to do, or it may not be. Before you jump, especially if you are a visual observer, set your C8 up next to that 4-inch TakaPhysics APO at the next star party, point ‘em both at M13, and have a look at similar magnifications. Maybe you should be enjoying what you have.

Periodic Error Terror

Telescope drive gears ain’t perfect. None of ‘em. Every set will have small defects that make them jig and jog over time, mostly in a regular and periodic fashion in the case of high quality gears. When I was a young feller, I figured all you needed to do long exposure astrophotography was a drive. Turn it on, open the camera’s shutter, and walk away. Any wonder my first pictures looked like I deliberately set out to do star trails? I learned a little more, tightened up my polar alignment, and tried again. A detectable (barely) but minimal improvement. Finally, I ran across a discussion of periodic error in a Sky and Telescope. Oh. You had to “guide.” That’s what them “driver correctors” was for. Dangit.

A lot of folks obsess about PE. How much error is too much? Twenty years ago, when I was just getting back into astrophotography after a considerable hiatus, “30-arc seconds” was considered quite respectable. Today, if you tell a prospective buyer a mount’s PE comes in at around that figger, the reaction is “Oh, it’s JUNK, huh?” 30-arc seconds, however, which most midline Chinese imports, like the CGEM and Atlas, come in at is easily good enough to produce excellent guided pictures, just as it was when I was shooting 35mm Fujicolor. Hell, now, with autoguiding and PEC, Periodic Error Correction, PE worries should be a thing of the past. They ain’t.

So why do folks get hung up on this? Because the periodic error of a mount is a quantifiable thing. It’s comforting to believe you can buy your way into good images if you just give Uncle Roland (or the Bisques or Takahashi) enough bucks for a mount with a low PE spec. Sad thing is, the first images from that wonder mount are usually not much better than those of a dadgummed Atlas. Even with a top-of-the line GEM, things like polar alignment and balance still matter. That is, astrophotography still ain’t easy. You cannot buy your way to good pictures. Getting to the holy grail of some folks, unguided imaging, generally requires not just a mount in the 10 grand-and-up category, but a permanent installation, and lots of cutting and trying.

Again, as with our other obsessions, I am not telling you not to go for the best mount you can get. In astrophotography, good gear does make getting good pictures easier. I’m just saying that not being able to afford an AP1200 doesn’t mean you can’t get good images. Even if you do eventually move up to a Hulk-o-matic German mount, the experience you gained with your Atlas or G11 will stand you in good stead. Gear is important in imaging, but experience is still what counts most.

Well, tarnation. We have just about run out of space and time (sorry, Professor Einstein). And I was worried about not having much to say. Summing up? You and me will likely always wish for More Better Gooder when it comes to telescopes. Cool astro stuff is a big part of the enjoyment many of us have in amateur astronomy. Which ain’t a bad thing. Not till it turns into obsession, anyhow. Till it makes you unable to enjoy the Universe with what you have. If you find that happenin’ to you, the cure is simple.

Turn off the pea-picking computer, get what you have out under the best skies you have, and push it. As hard as you can. I don’t mean 5-minutes on M42 and then back inside to watch yet another episode of Jersey Shore, either. When you are done, consider the wonders you have witnessed. No, that still won’t entirely silence the little voice that whispers, “But Uncle Rod, with an HD 1400 you could…” But it keeps me happy enough with the humble telescopes I have that I can leave tomorrow’s telescope to tomorrow.

Finally, y’all, HAPPY FAT TUESDAY! Don’t do nothin’ I wouldn’t do! Excelsior…

Comments:
I have always said any telescope is better than none. That is what I have now, as I am in California and my telescopes are clear across the country in storage in New England.
 
With that CGE Pro 1400 HD, you'll shoot your eye out. :) Great post.
 
It is easy in our society to get caught up in the aquisition fever. I think we have all been there at one time or another. This year I plan to go digital (astrophotography) and I figure that will keep me busy for a LOOOONNNG time with what I have (8" SCT). This was a good read....thanks!
 
Hi Rod,
(I know this is a late post, which is to my point.) I have been thinking of a big dob to compliment my 9.25. Set the SCT for imaging then gander using a 14+ dob. I think about it until I realize that I only get to a dark site 1 or 2 times a year now. Got promoted at work, kids take more time, yada yada yada. When I use the time available vs. the cost of a "nice to have", well I'll just say that 9.25 is still king of aperture for me.

Good entry. I know that in my few years in this hobby, I have been part of the hysteria on each of your points. I have had a bunch of good people (like yourself) point me in the right directions though. The end result? Smiles when I get to use what I got.
 
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