Astrophotography 101
March 3, 2015 4:31 AM   Subscribe

So I recently bought a T-mount (with a 2x Barlow) to attach my DSLR to my 6" Dobsonian reflector telescope. Whilst this gives me great images of the moon and I managed to capture a decent fuzzy picture of Jupiter, I know I'm going to have to upgrade my gear to start capturing deep sky objects...

...from what I have read a decent equatorial mount with a drive system to allow long exposure photos (to track the rotation of the Earth) is key. Also, I'd like a new telescope that's a little more portable than my present, rather unwieldy, Dobsonian. I know that a refractor or Schmidt-Cassegrain might be the answer (I know apochromatics are great but pretty expensive).

I'm looking to spend no more than c. £800 ($1000)- what's the best eq mount/telescope combination I can get for that kind of money? (Lots of websites out there but would appreciate some personal insights from the hivemind). Cheers!
posted by Rufus T. Firefly to Sports, Hobbies, & Recreation (6 answers total) 10 users marked this as a favorite
 
I'm not an expert, but have some familiarity with this subject; a few years ago I was more or less in your position.

A lot of this depends on what you want to take pictures of -- how long and deep you want to go. Different sky objects have different requirements. But in general this stuff gets real expensive, real fast.

Wide-field astrophotography can be done with a camera lens and a star tracker. Star trackers are basically light-duty equatorial mounts that you usually attach to a camera tripod (sometimes the tripod is included); products include the iOptron SkyGuider and SkyTracker, Sky-Watcher Star Adventurer, and Vixen Polarie. When you're shooting through a normal, non-telephoto prime lens (under 200 mm), precise polar alignment and tracking isn't as critical for long exposures as it is when your focal length is 2,400 mm (the focal length of a 6″ Dob with a 2× Barlow). Larger nebulae and galaxies (Andromeda is a wide-field object, for example) do well with this sort of setup. I have no personal experience with this sort of thing, but I've been following it. This is probably the better place to start.

Shooting at prime focus through a telescope is different. In my opinion, the scope is less important than a sturdy mount and an accurate polar alignment. The minimum mount I'd want to use for astrophotography would be something like my own HEQ5 Pro, and then only with a relatively small and compact scope. (Mine has been rock-solid with an 80mm f/6.25 apo doublet and a 125mm f/10 Schmidt-Cassegrain; it was wobbly the time I tried it with a 200mm f/5 Newtonian: long scopes are bouncier.) And, the deeper the field and the longer the exposure, the more that mount stability and polar alignment count. Astrophotographers will also use an autoguider -- a small secondary scope/camera/computer combination that corrects the alignment of the mount -- to stay precisely on target. (Most equatorial mounts have autoguider ports.)

As I said, a few years back I spent a lot of time looking into this and was frankly defeated by the expense and steep learning curve.

Anyway, what do you want to take pictures of?
posted by mcwetboy at 6:47 AM on March 3, 2015


Astrophotography is a subject which can range from a pleasant pastime for taking nice pictures for fun to what can be called an obsessive-compulsive disorder - you've been warned! ;-)

Rather than dive into the many aspects, I'd suggest you look here as this is a good introduction with lots of links about what you want in a telescope. However, it focuses almost exclusively on telescopes and the fact of the matter is that if you are going to try to get good pictures of deep sky objects, you will also need to become familiar with software for "stacking" images. Many amateur scopes are hard to get properly aligned, balanced and leveled (even with good onboard computers), for long exposures. instead, you will probably want to take many shorter (~15 secs) images and then combine them using software. Combining the images will produce more detail, better color and clearer images if done right. Here is a review page of some of the stacking software that's available.

Good luck and have fun!
posted by BillW at 7:00 AM on March 3, 2015 [1 favorite]


Hey, that's a great answer mcwetboy. Ideally, I'd like to take some nebulae (e.g. Orion) and maybe some open clusters (e.g. Beehive), getting a few nice planetary images (e.g. Saturn) would be good too. Is there some kind of trade-off between scopes that are best for planets and those for nebulae etc?

I know things can get absurdly expensive. But I would be happy (for now) with a relatively basic set-up. I guess there is also the option of stacking images for good captures (but I know very little about that particular art).
posted by Rufus T. Firefly at 7:03 AM on March 3, 2015


It's a question of angular diameter: something only a few arcseconds across will require a longer focal length to appear a reasonable size than something a few degrees across, and vice versa.

Some sizes (1 degree [°]= 60 arcminutes [′] = 3,600 arcseconds [″]):
• Mars: 3.5″-25″ (depends on orbital position)
• Saturn: 15-21″ (ditto)
• Jupiter: 30-50″ (ditto)
• Moon: 29-34′ -- about half a degree
• Orion Nebula (M42): 65′ × 60′ -- about a degree square
• Beehive (M44): 95′
• Pleiades (M45): 110′ -- nearly 2° across
• Andromeda Galaxy (M31): 190′ × 60′ -- about 3° × 1°

The question is, what is your field of view when you've hooked up your camera via prime focus to the telescope? Is it too wide to be able to see Saturn, or too narrow to see open clusters? Some choices may need to be made.

(There's a reason why Andromeda is usually photographed as a mosaic: most telescopes wide enough to capture M31 in one shot don't have enough aperture to get enough detail in a reasonable exposure time.)
posted by mcwetboy at 7:41 AM on March 3, 2015


You should look around over at the Cloudy Nights forum if you haven't already.

Last year I bought a Celestron Advanced VX mount for my 8" Schmidt-Cassegrain. It took some shopping around to find the right dovetail to get the two working together but I eventually got it. I've been very happy with the mount, it tracks well for viewing even with a rough alignment and it should be good enough for some shortish exposure DSO photography. I have a T adapter for my dSLR and, like you, I've done some lunar shots and some blurry planets.

I bought my scope on eBay years ago. I think an 8" SC is a pretty decent scope to get started with while still being portable enough to lug it around if you need to. Really the mount is the most important part of this so that's where you want to spend a good chunk of money. Get the most stable one you can afford.

If you can fit your scope on a better mount I would get a mount first and then upgrade your scope once you've saved up some more money. Once you have an EQ mount that is properly aligned and tracking the stars you can also get an adapter to piggyback your camera onto the scope (on the back of the scope rather than looking through it) and take some wide field shots with your camera lens. This is a good way to learn the ropes.

There is a big used market for this sort of stuff. A lot of people get into it, find it's way too much work, and then sell off their gear.

I live in a light polluted area (Boston suburbs) so I haven't attempted too many DSOs. Here's a 10 second exposure of the cluster in Hercules as an example of what can be done without too much advanced equipment (no auto guiders) or experience. That's one of the few DSOs that are worth attempting in my area.

Most of the best planetary photos I've seen that were done by amateurs were done with imagers such as the Celestron Skyris and then stacked using software. The idea is that, since the air you're viewing the planet through is unstable and blurry, if you take enough photos in sequence you'll have brief moments of stability and then the software averages out all the "decent enough" shots to give you a clear shot. There are some amazing things being done with this sort of thing. I've been thinking of investing in one.

I've never quite been able to figure out stacking using programs like Registax, but my understanding is if you want to get into this you have to learn how to do it. Almost any decent astrophoto you can find has been stacked and processed out the wazoo. That doesn't mean they're all being created in Photoshop, not at all. They're using software to enhance the data that they've collected, not to create that data.

I think the key to getting started with this hobby is lowering expectations. We've all seen those amazing color photos of galaxies and nebula that people have done. Get that out of your head right now. You're not going to take those, at least not yet. Those are possible but require a huge investment in money and experience. They're also heavily processed with software after the fact. For the first few years you need to be satisfied with grainy shots of the Ring Nebula or a fuzzy planet. Forget about getting a decent galaxy shot for now.

It's a big black hole of money. Once you have the mount and scope then you find out about autoguiders and imagers and before you know it you need a dedicated laptop and then you're building an observatory in your back yard and it never stops. If you can be happy with every attempt, and happy with what you've done with your current setup, you can avoid getting sucked into it.

That said, when a faint smudge turns into a spiral galaxy after a 20 second exposure, and you took that shot, even if it in no way compares to what you might see in a magazine it's still a pretty great experience.
posted by bondcliff at 7:51 AM on March 3, 2015


You are at the beginning of a demanding, expensive, frustrating hobby. Here's a good introductory article that will give you some context. The astrophotography subreddit is remarkably good; their wiki has lots of resources on it. And seconding the Cloudy Nights forums as the place to hang out and learn more.

My basic advice is to focus more on image processing software rather than image acquisition hardware. When I look at amateur astrophotography it's always the quality of processing that stands out. I keep thinking there's a way to do good astrophotography work without your own telescope; just take raw image data off of the Internet and do all the hard work of processing it. There's a lot of excellent imagery from robotic telescopes available for free.
posted by Nelson at 10:35 AM on March 3, 2015


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