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Tracking mount for DSLR astrophotography

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#1 laidman

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Posted 19 April 2012 - 10:58 PM

Hi everyone!

I've got a question regarding mounts. I've tried to search for it elsewhere, but haven't really able to find any good results.

I've had an interest in and done some rudimentary astrophotography over the past 7 years or so and am interested in getting a mount to allow for long exposures. I don't plan on using/buying a telescope anytime soon, so this would be used 100% for through-the-lens DSLR shooting.

Are there some reasonable options out there? I'd like something that can track well at telephoto lengths up to 500mm or so (plus I also have a 2x extender). As I'm using a crop-sensor Canon body the actual focal length could be 1600mm I suppose...

If I want to do longer exposures (5 mins plus?) at those focal lengths are there any reasonably priced options out there? Preferably something under $1000...But then again I'd like something that can perform and won't hold me back.

Thanks folks!

#2 powerstroke01

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Posted 19 April 2012 - 11:06 PM

http://www.losmandy.com/starlapse.html

#3 Falcon-

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Posted 20 April 2012 - 12:53 AM

I would probably stick with 500mm and lower - not bother with the 2x extender. Going up to 1000mm at a slow focal ratio is not the best way to image.

As for mounts I have a few ideas:

- The Lostmandy Starlapse looks like an interesting option!
- Astrotrac makes a very portable DSLR imaging rig
- The basic Celestron CG-5 ASGT and (mechanically identical) Skywatcher EQ5-Pro mounts are a bit heavier to lug about then the first two options but make good DSLR imagers. I personally own a CG-5 and use it for camera lens imaging.
- The new Meade LX80 may be a good option (it SOUNDS good, but it has yet to actually ship....)


That all said, *IF* you plan to move up to imaging with a telescope at some point in the future (and do not need the ultra portability of an Astrotrac or Starlapse) then you should seriously consider a Celestron CGEM, Orion Atlas EQ-G or Skywatcher EQ6. Those three mounts are in a class above the CG-5/EQ5 and very capable of long focal length imaging.

Hope that helps!

#4 Midnight Dan

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Posted 20 April 2012 - 06:26 AM

Hi laidman:

I don't plan on using/buying a telescope anytime soon


If you're using lenses in the 500mm to 1600mm range, then you ARE using a telescope right now! At those focal lengths, you will have all the same issues tracking as you do with a telescope, and your mount requirements will be the same. There is no difference.

An 80mm refractor commonly used for wide view AP would be around 500mm. A 4" refractor might be 700mm or so. Small to medium sized SCTs are in the 1000 to 2000mm range. All of these would need guiding for a 5 minute exposure on a reasonably priced GEM.

There are no mounts I know of in the sub $1000 range that will track for 5 minutes at those focal lengths. In fact I think you'd have trouble finding anything for less than $5000 that will go for 5 minutes unguided. To get that kind of performance, you'd probably need to be shooting at 200-300 mm or less, spend more on a mount, take shorter exposures, or guide.

If budget is the primary constraint, the CG-5 is a good option, and the Meade LX80 *might* be good once it ships.

-Dan

#5 tezster

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Posted 20 April 2012 - 08:00 AM

What do people here think about the Vixen polarie for wider-field, short exposure shots? Seems like an inexpensive way to get your feet wet in astrophotography?

#6 terry59

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Posted 20 April 2012 - 09:49 AM

What do people here think about the Vixen polarie for wider-field, short exposure shots? Seems like an inexpensive way to get your feet wet in astrophotography?


Take a look at this thread

#7 laidman

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Posted 20 April 2012 - 10:10 AM

Thanks for the links everyone!
It's bedtime here...and raining...so I'll give all those a good look over in the morning.

Out of curiosity, where is the crossover between wide-field and close-field(?) imaging?
It seems like a lot of wide-field images are actually taken with lenses/scopse at a short telephoto focal length.

Also, for guiding, it seems like another camera or imager of some kind is needed, right? So taht second camera takes shorter pictures, feeds them to a computer where the software analyzes them and then makes minor tracking adjustments?

Night all!

#8 Falcon-

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Posted 20 April 2012 - 01:57 PM

As far as I know there is no real definition between wide and close. I know what *I* consider to be my long focal length scope is considered by some to be medium wide for example...

I tend to think of it something like this:

- under 100mm: ultra-wide
- 200mm and lower: Very-wide
- 200-400mm: Wide
- 500-900mm: Medium
- Higher then 900mm: Narrow/close

My own AP setup consist of camera lenses from 28mm to 300mm, a 912mm focal length scope and a 1370mm scope. I agree with the idea of thinking of a long focal length camera lens as a telescope in it's own right - I certainly think of my massive Tair-3 lens as my "Widefield Astrograph Refractor" :)

You are correct that auto-guiding requires a second camera. You do not however need (or want) that second camera to be a DSLR or anything high-end... you can even use a modified webcam if you can find a bright enough star to guide with. Many people use a converted 50mm finder scope and a guide-camera as it is light, relatively inexpensive, and quite effective. You can buy pre-made finder-guider packages these days...

BTW What lenses do you actually have?

#9 nganga

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Posted 20 April 2012 - 02:20 PM

Hi everyone!

I've got a question regarding mounts. I've tried to search for it elsewhere, but haven't really able to find any good results.

I've had an interest in and done some rudimentary astrophotography over the past 7 years or so and am interested in getting a mount to allow for long exposures. I don't plan on using/buying a telescope anytime soon, so this would be used 100% for through-the-lens DSLR shooting.

Are there some reasonable options out there? I'd like something that can track well at telephoto lengths up to 500mm or so (plus I also have a 2x extender). As I'm using a crop-sensor Canon body the actual focal length could be 1600mm I suppose...

If I want to do longer exposures (5 mins plus?) at those focal lengths are there any reasonably priced options out there? Preferably something under $1000...But then again I'd like something that can perform and won't hold me back.

Thanks folks!


5-minute exposures at 500mm or more is really in the realm of guided astrophotography. You would have to get a traditional GEM and all the trappings.

For more modest focal lengths with camera lenses, Astrotrac would be a great choice. Tracking accuracy is phenomenal. The one tricky problem with Astrotrac is that you would need to collimate the polarscope in order to get very accurate polar alignment for those extended subexposures. A lesser irritation is that Astrotrac tracks for just about 2 hours before it has to be reset.

I have not used the new Losmandy mount or the new entry from Vixen. I have read a review of the Takahashi Eclipse, another portable camera tracking mount, by Tony Hallas, but I have not used one either.

Hope that helps.

Clem.

#10 laidman

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Posted 20 April 2012 - 09:33 PM

@Falcon- hmmm, that's strange to me, coming from regular photography...100mm being ultra-wide!
As for lenses, I've got a Canon 50mm f/1.8, 17-55 f/2.8, 70-200 f/4, 100mm f/2.8 macro, Sigma 150-500 f/6-6.3, and a Kenkon 2x extender. My camera is a Canon 40D with battery grip.

@nagnga - I've tried to quicky educate myself on subexposures...those are the shorter exposures that expose for the brighter areas of what you're trying to image, right? Or is it the other way around? Anyway, subexposures are still light frames, yes? I've done a bit of playing around in DeepSkyStacker and am only used to lights, darks, biases...

Maybe these questions should go in the Beginners' forum...sorry!

Thanks again

#11 Falcon-

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Posted 20 April 2012 - 10:01 PM

As for lenses, I've got a Canon 50mm f/1.8, 17-55 f/2.8, 70-200 f/4, 100mm f/2.8 macro, Sigma 150-500 f/6-6.3, and a Kenkon 2x extender. My camera is a Canon 40D with battery grip.


The Canon 40D is an excellent astrophotography camera. :)

You will probably find that your 50mm and 100mm prime lenses are of the most use, though certainly try the others as well. Keep in mind that with most lenses you will need to stop down a few notches from full open for best performance... for example the 50mm f/1.8 is *terrible* at f/1.8, but extremely good at f/4 or f/4.5 (your more expensive lenses may perform better, but rare is a lens that can be used wide open).

The tele extender, unless it is a lot better then the few I have seen, will likely add too many optical aberrations to be worth it.

I would be very curious to see the results with the Sigma!

I've tried to quicky educate myself on subexposures...those are the shorter exposures that expose for the brighter areas of what you're trying to image, right? Or is it the other way around? Anyway, subexposures are still light frames, yes? I've done a bit of playing around in DeepSkyStacker and am only used to lights, darks, biases...



Sub-Exposures in this context are simply multiple exposures of the same area all with the same settings and exposure lengths. In DSS's terms they are the Lights.

Maybe these questions should go in the Beginners' forum...sorry!



Feel free to stop into the DSLR imaging section of the forums and you might consider Jerry Lodriguss' books as well (Jerry is a CN forum member here).






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