Sunday, March 10, 2013

 

Instamatic Astrophotography


No, I don’t mean we’re literally going to use that darling of 1960s snapshooters to take deep sky astrophotos, but almost, muchachos, almost. If you’re interested in imaging the sky, that is, which some amateurs are and some are not. Why ain't everybody an astrophotographer? Some folks genuinely don’t like the idea. They’ve never tried taking pictures but are pretty sure they wouldn’t like it. For them, contemplating the Universe through an eyepiece is fun and relaxing and that is enough and good on ‘em.

I suspect, though, that a lot of amateurs who’ve actually tried imaging and have dropped out of what Unk calls “The Difficult Art” have done so not because they don’t like the idea of capturing the Universe, but because it all seems too much. Too complicated. Too expensive. No pretty color prints of M42 for them then, right? Nope, it’s easy to take nice deep sky astrophotos from the get-go without a lot of fuss if you keep it simple with Unk Rod’s Instamatic Astrophotography System.

I know you’ve been told how to get started in astrophotography:  begin with star trails and move up to piggybacking. That is still good advice. If nothing else, you get used to taking a camera and its accessories into the field and begin to learn about dew, light pollution gradients, and all the other gremlins. And I guess the majority of new imagers still get started this way. But very few want to remain with wide field vistas or star trails for long. Most aspiring deep sky imagers want to take pictures through the telescope as soon as possible.

Problem is, going from star trails snapshots or piggyback astrophotography to through-the-scope prime focus work is one heck of a big jump. Mainly because of the guiding part of the long exposure equation. As you may know, the telescope mounts most of us can afford are not capable of long exposure imaging—taking shots of more than a minute or two in duration—without guiding. Small imperfections in gears mean that if a “guide” star is not continuously monitored and small corrections made to the mount’s aim, stars will wind up off-round, and no astro-imager wants that.

Autoguiding ups the gear factor and the aggravation factor several fold. If you, like most folks in these latter days, want to guide automatically, you need a lot more stuff than just a telescope, a mount, and a camera. You need a separate guide camera (unless you are using an expensive CCD cam equipped with self-guiding), and you need something for the guide camera to look through, a guide scope or an off axis guider. Finally, you will probably need a computer. There are a few guide cameras that don’t require a PC, but the more affordable ones don’t work very well.

You also need a lot of patience and experience. It sometimes takes months to get a guiding system working reliably. You may luck out and get round stars the first night out with the default settings in your guide software, but you may instead find you need to spend plenty of nights fine-tuning everything from software to the guide scope mounting. Luckily for enthusiastic imaging newbies, you can, like Uncle Rod, cheat.

Well, you’re not really cheating, but you are making things easier on yourself. The secret to my approach is dispensing with as much stuff as possible. Guide scope? Leave it at home. Guide camera? It stays there too. Five thousand dollar CCD camera? Fuhgeddaboutit. You may even be able to let the cotton-picking laptop PC sit in its case. This is Instamatic Astrophotography, a way to get simple but attractive color snapshots of the deep sky in minimalist fashion. The images us celestial tourists get this way are a lot like the snapshots taken by terrestrial tourists:  humble but loveable.

If you haven’t guessed already, what I am talking about is unguided imaging. Yeah, I know what some of the gurus on the dadgum Cloudynights.com will tell you:  “Won’t work. Not unless you have an Astro-Physics or Software Bisque Mount (to the tune of about 10k).” Lucky for you greenhorns your old Unk is here to tell you ‘tain’t necessarily so.

What’s the secret? There are several. First, you want to start out with the best-behaved mount you can afford. No, you do not need a Mach 1, but you want something better than a pea-picking EQ-1. If you have an Atlas EQ-6 or a CGEM or iOptron’s iEQ-45, you are golden. Those lower middleclass mounts, though, a can still be too much for a cash-strapped newbie who’s just invested in a camera, an OTA, etc., etc. The answer is Celestron’s inexpensive CG5 (now being replaced by the better but similarly priced VX). It’s not necessarily “the best” for our purposes, but it is the “good enough.” Meade’s now-discontinued LXD-75 will also do the trick, if not quite as reliably, and is even cheaper.

Quite a few astrophotography beginners have alt-azimuth mode scopes like the basic Celestron NexStars or the Meade LS. The Celestrons can be used in equatorial fashion, but that requires a wedge that costs money. The Meade LS cannot be used equatorially at all. The good news is that at the relatively short exposures we will be using an alt-az can do OK, though a polar aligned mount will do better. A GEM or fork on a wedge only has to track in one axis, not two like an alt-az. Alt-azimuth tracking doubles the possibility of tracking error.

Next is the scope. Tracking errors are magnified by long focal length, natch. What you want is a telescope with a reasonably short focal length. Maybe 600 – 1200mm, with something on the lower end being better if your camera has a small sensor chip. If you have a telescope in that focal range, maybe a small ED refractor, cool. If not, many, including SCTs, can be made to fill the bill with a focal reducer.

Then there is set-up. There are two things to consider here: balance and polar alignment. If your mount is to perform its best, balance is critical. That’s true for any equatorial mount, but even moreso of those in the CG5 class. How do you balance? Slightly EAST HEAVY. When the R.A. lock is disengaged, you want the tube to slowly move to the east.  If you are a little east-heavy, the drive will pull the telescope along; the gears will remain in contact with each other, minimizing tracking errors.

Believe me, campers, balance makes a big difference. Naturally, you will have to redo your balance when you switch from imaging on the east side of the Meridian to the west, so it’s usually best to confine the evening’s targets to one side of the sky or the other. Also, let me emphasize that when I say “slightly east heavy,” I mean slightly. Having the scope way out of balance in R.A. will make tracking worse rather than better.

How about declination balance? That is not as critical. If you were guiding the telescope, you might want the balance slightly biased in one direction, north or south. But you are not, so just balance well enough in declination the mount doesn’t strain during go-to slews and don’t worry about it.

The last set up consideration is polar alignment. If you don’t have a good polar alignment, stars will trail in declination due to something called “field rotation” no matter how well the R.A. motor and gears do their job. To minimize this declination drift, you want to achieve as good a polar alignment as possible. Doing a full-blown drift alignment is best, but if you are like Unk and don’t have the patience for that, some of the “almost as good” alignment methods outlined in the linked blog post above work fine.

How about exposure times? That is the crux of the matter. The key. The out. Stay at 30-seconds. Your mount may be able to go a little longer unguided—sometimes—but 30-seconds will ensure the greatest number of “keeper” sub-frames. You won’t get too much detail in dimmer objects at 30-seconds, and the exposures will look pretty noisy, but you can take lots of 30-second exposures and stack them into a final picture that does show plenty of detail. It is always better to expose subframes for as long as possible in the interest of keeping noise down, but 30-second stacks will look right good to you in the beginning.

Finally, there’s the question, “Which camera?” A DSLR is probably the best choice. And a Canon DSLR is still what you pick if you’re into astro-imaging, all things being equal. The DSLR, no matter who made it, has several important advantages for the beginning imager. It is wonderful for terrestrial use if you decide astroimaging ain’t for you, and it is easy to use in the field by itself without computers and a lot of support gear.

Even more importantly, it has a relatively large chip. The APS sized sensors found in the lower cost DSLRs are as big as, or usually considerably bigger than, what’s in all but the more expensive astronomical CCD cameras. In addition to giving you a large field for framing big objects, a larger chip makes the camera more forgiving of a mount’s go-to accuracy or lack thereof. Also, the “magnification” factor of the chip is low. Smaller chips exaggerate guiding errors. The image covers a smaller area of sky than with a larger chip, making even slightly non-round stars look worse than they otherwise would.

Which doesn’t mean you shouldn’t consider a CCD camera. If you don’t have much money to spend and/or don’t need a camera for earthly shots, an inexpensive CCD might be the way to go in the beginning.  A bottom-of-the-line CCD, Meade’s original DSI, is what Unk got started with eight years ago when he decided to finally buckle down and learn astrophotography the electronic way. In addition to being cheaper than DSLRs, these cameras have another advantage:  their imaging chips are small, but they are more sensitive than those of DSLRs, particularly to red light, which is very important if you fancy shooting nebulae.

What’s out there in the (well) under-1000 dollar CCD camera range? There used to be a lot more to choose from, but with Meade and a couple of others leaving this section of the market, I am only aware to two widely available choices at the moment, Orion’s StarShoot G3 cameras, available in one shot color or black and white for about 400 bucks, and Starlight Xpress’ Lodestar for $699.00. One other possibility is the QHY-5II, which seems similar to the Lodestar. It is quite inexpensive at $245.00, and appears to have promise, but I don’t have any information beyond that.

Which would I choose? The Lodestar is capable of producing nice pictures, but is intended more as a guide camera than an imager and is not cooled. Same with the QHY. The Orion is cooled and produces smoother looking, more noise free images without a lot of post-processing hoo-doo. Color or black and white? Color, surely. Most novices want color and do not want to fool with filter wheels and tricolor imaging to get it.

Novices often ask if there ain’t a third way, a cheaper solution than a DSLR or a CCD camera: “Unk, can I take astrophotos with my point and shoot camera?” You can—of the Moon and planets. Just shoot into the eyepiece in afocal fashion and you can get some nice pix in the beginning. Unfortunately, these cameras just aren’t up to the task of deep sky imaging.

If your wallet or purse is feeling light, be assured there is a cheaper way. Meade, as above, discontinued its DSI CCD cameras a couple of years back. They made plenty of them, though, so they are common on the used market. The Meade DSI and DSI II are inexpensive used, and while they are not cooled, clever hardware design means they do a better job keeping thermal noise at bay than you would think. The DSI III? It’s a goodie too, with the difference between it and the earlier cams being a larger chip. Unfortunately, it sold for considerably more than the early DSIs and still goes for a fair amount used. Even the basic DSI I can do surprisingly well; all the astro images in this blog entry were done with it.

What else do you need? The Orion, the QHY, and the Lodestar all require a computer for operation. Most DSLRs can take 30-second shots without even a remote (“cable”) release, much less a computer, but having an inexpensive camera remote makes DSLR shooting way easier and is practically a necessity. Without one, you’ll have to fool with the self-timer so you don’t shake the scope when you take a shot. The Orion cameras are powered by the USB bus, but their coolers require an external 12-volt battery for operation.

Camera, mount, and scope in hand, let’s set up on the observing field and do an Instamatic run. With the scope balanced for whichever celestial hemisphere you will be imaging in, the next step is polar alignment. How you do that is up to you, whether by drift aligning or taking an easier way out. I center Polaris in the hollow bore of the CG5’s RA axis (I did not buy and don’t need or want a polar alignment borescope) and do Celestron’s AllStar polar alignment, which is more than good enough for 30-second exposures.

How about PEC, periodic error correction? If your mount has it, use it. Details will vary with the scope model, but you pick a star, a reasonably bright star, in the area of your target. Center it in an illuminated reticle eyepiece and start the PEC recording process. Watch the star, and if it drifts in RA re-center it using the hand control (which is set to “guide” speed). When the recording is finished, begin playing it back, however your particular scope has you do that. PEC will almost always result in a higher percentage of 30-second keepers.

Next item on the menu is attaching camera to the telescope. How you do that depends on the camera and the scope. If you are using a DSI or one of Orion’s CCDs, it’s easy. Those cameras come with a 1.25-inch adapter that slides into a focuser or a visual back. If you are using an SCT, that visual back will be screwed onto an f/3.3 focal reducer. DSLR? You will need a widget called a “prime focus adapter” and a T-ring that takes the place of your camera lens. The T-ring threads onto the prime focus adapter, which then screws onto the (usually f/6.3) reducer on an SCT or slides into the focuser of a Newtonian or refractor.

Fire up the camera next, and make sure you have plenty of fire. The small CCD cameras are powered by the computer over their USB cables, so you wouldn’t think that would be a problem. Well, it is. Your computer supplies them with power, and can only supply the amps they need if it has sufficient power available itself. Even if your computer’s internal battery will furnish enough current to keep the PC alive for the whole observing run, run it from an external 12vdc battery and an inverter to ensure it has enough extra power to keep the camera going.

DSLR batteries do pretty well—in the daytime when they are warm, anyhow. On a cold observing field where they will have to hold the shutter open for 30-seconds exposure after exposure? Not so much. My Canon Rebel’s battery will last a couple of hours, but no more. Solution? An extra battery or a battery eliminator, which most companies sell for their cameras. You will probably need a small inverter and a battery to go with a battery eliminator, since most are designed to use AC mains current.

Time to start shooting. Well, start focusing, anyway. That’s duck soup with the li’l CCD cams. Meade’s Envision software for the DSI and the programs shipped with other CCD cameras, have focus utilities that allow you to get a star focused without a hassle (I generally rough focus on the last go-to alignment star and fine-tune on dimmer stars in its field). Focusing a DSLR that has “live view”—that presents a constantly updating live image on its display screen—is not too bad. Focusing a DSLR without live view is absolute murder if you are not running the camera with a PC and a program like Nebulosity.

When you are OK with focus, it’s rubber meets the road time. Go-to your first target. Most current mounts won’t have any trouble putting it on the large chip of a DSLR. The tiny chip of an inexpensive (or older) CCD? If your object is not visible in the field when the scope stops no matter how you up the exposure, engage “Precise Go-to.” Both Meade and Celestron mounts feature this utility, which ensures you get on the target every time.

When you select an object with Precise Go-to enabled, you will also be asked to choose a bright star in the neighborhood of the DSO, usually from a list. Do that and the scope goes to that star first. Center it, press the “go” button, and the mount/scope proceeds to the target. You can be pretty much assured it will be in the field of even the smallest chip every time; usually near the center. Precise go-to would be a pain for normal observing, but when you are imaging, you’ll usually only do a few objects per night, so it is not too much of an annoyance, and is certainly easier than hunting around for your subjects.

Then you start taking 30-second subframes. As many as possible. At least 25 for most objects; more is better. The more subframes you have for stacking, the better exposed and less noisy the finished image will look. Doing a lot of subs is easy with a CCD or when you’re operating a DSLR with Nebulosity or a similar program; you just tell the software to expose 25 shots and walk away. No Nebulosity? You will have to manually trigger each DSLR shot. Once again, at least having a remote/cable release “interval timer” makes DSLR shooting easier, much easier.

And so the camera clicks off exposure after exposure of M13. What can you expect of ‘em without guiding? If you’ve carefully balanced the telescope, you can expect most of them to be pretty good. If you’ve got PEC running, a large majority will have un-trailed stars. You cannot, however, expect every single one to be OK with a CG5 class mount, or even with a mount in the next tier up. There will always be some you have to throw out. An errant gust of wind, a bad spot in a gear, or one of the numerous unidentifiable gremlins that plague astro-imagers will always send some to the trash.

When you’re back home cozy and warm, the next step comes: stacking and processing. That is the subject for a whole blog entry some Sunday, I reckon. But modern programs like the free Deep Sky Stacker and the inexpensive Nebulously (which does a hell of a lot more than just stack frames) make stacking and combining sub-frames nearabout painless. A little tweaking of brightness/contrast/histogram using the image processing part of your stacking program or a separate program like Photoshop and you are done.

As I warned in the beginning, your pictures will not make Jason Ware or Robert Gendler sweat, but they will be yours and you will love them. Heck, even years and lots of imaging experience down the road, some of my 30-seconders still look right nice to me, muchachos. If nothing else, you’ll have leapt into those scary deep sky-imaging waters with both feet. I’ve since gone on to autoguiding and all that stuff, but I still enjoy and use the simpler way, good old Instamatic astrophotography.

Next Time: Comet Fever?


Comments:
Another excellent article, Rod. Looking forward to Comet Fever as well.
 
The lower middleclass mounts have a greater load capacity, and maybe more features, than the inexpensive ones. Are there other significant differences that affect performance even if one is careful about load?

Kendahl
 
Sometimes--but not always--a better periodic error figure.
 
I have taken the plunge going from pure visual to instamatic astrophotograph and it is extremely addictive. http://darrenwastro.blogspot.com/2013/01/astrophotography-revisitedcmos-and-ccd.html?m=1. Love your articles...one of the things I look forward to every week
 
Rod -

My LXD 75 and Nikon 7000 work very well. One big thing is that the D7000 has an intervelometer, and I can have it take 3 or 4 hours (on one battery) without ever touching the the setup.

Very nice write up. BTW did 23herschel 400 Galxies Friday and Saturday with the club (21 degrees - it was cold).
 
Another great blog. Extremely informative and dead on!
With all the video cameras and CCD cams I have I do find myself going back to the simple days of digiscoping (A-focal). I have found the Lumix digital cameras go up to 60sec exposures and the quality of the optics and chips have made this fun to do again. Especially having the ability to mount eyepieces directly to the camera with readily available adapters. Shoot, I am even seeing reasonably good results from iPhones posted on the internet. It will be fun to see where all this technology leads to in the next few tears.
 
Another great blog. Extremely informative and dead on!
With all the video cameras and CCD cams I have I do find myself going back to the simple days of digiscoping (A-focal). I have found the Lumix digital cameras go up to 60sec exposures and the quality of the optics and chips have made this fun to do again. Especially having the ability to mount eyepieces directly to the camera with readily available adapters. Shoot, I am even seeing reasonably good results from iPhones posted on the internet. It will be fun to see where all this technology leads to in the next few tears.
 
Don't forget to look at BackyardEOS for managing your DSLR. It made all the difference for me. It makes imaging really simple, once you get the dad-blamed telescope pointing in the right direction!
 
Also have look at http://www.ideiki.com/astro/ .
This peace of software is real cool and has got a ton of features.
The only one i know that has a bahtinov focusing tool. Give it a try and kinda cheapo too.
 
Also have look at http://www.ideiki.com/astro/ .
This peace of software is real cool and has got a ton of features.
The only one i know that has a bahtinov focusing tool. Give it a try and kinda cheapo too.
 
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