Astrophotography scope troubles: Which to buy?
Posted 05 December 2012 - 02:39 AM
I have been in the process of acquiring an AP Setup for a few months now, mostly doing research on products and prices that could afford good astrophotography on a budget.
I started with purchasing an Equatorial Cg4 mount and have picked up an Imaging source camera too. I already have a canon dslr that I can use for long-exposures, so I am mostly trying to search for an OTA that would be appropriate to use.
After reading many reviews, I narrowed affordable scopes downs to an 8" Orion Astrograph f/4, AT6RC, or possibly a Stellarvue 70ED.
Right before purchasing an AT6RC, I read about the Orion 80ED refractor ($450 Amazon). Now I am back at square one!
I mainly want to use the scope for DSI and Planetary imaging (Jupitor/Saturn), and now just again at a loss of what might be the best next step into the field. Would a refractor like the Orion ED really offer similar photos than a reflector/Ritchey-Chretien?
I have not owned a reflector yet (just a cheap meade refractor), so I don't think I would be missing collimating or taking the extra dew precautions needed by reflectors (unless they are the better choice and worth the extra effort).
I am not looking for a super beginner scope either, have been meddling around taking photos through a cheaper setup and with my f1.8 50mm canon lens to feel comfortable going to the next level.
Posted 05 December 2012 - 10:24 AM
Mirror scopes are troublesome beasts for AP. I've been imaging for several years now and I'm still enjoying my 80mm APO very much.
Posted 05 December 2012 - 10:28 AM
Posted 05 December 2012 - 11:21 AM
After that, I would seriously look at TV101NP - which is not exactly TV101is, but very similar, and generally a good buy, if bought used.
AT111 (also listed on CN and A-mart) is another gem for imaging. Also look at ES127 (or other such variants, especially used - although, I would recommend the ES over all other Chinese brands) - one of the better made Chinese scopes for imaging and the aperture and F/L are great for both DSOs and planets. The only drawback on both the AT111 and ES127 is the focuser - you will invariably want to change it at some point - although, with the current setup, you might be OK. Same is the case with EON120 from Orion, but definitely worth considering.
On the smaller side - you might want to think of AT65EDQ (or the Chinese version).
With most of the above scopes - except for the 4 element versions, you will find that you will need flatteners or even a reducer for very wide DSOs.
Hope I've helped narrow the choices. Please let us know, with pictures, what you end up with and how much you like/dislike it!!
Posted 05 December 2012 - 12:06 PM
I'd like to point out one limiting factor: Your mount.
The CG-4 is a fairly lightweight mount, as far as imaging goes, which means you're best served by a light, fast scope (think widefield). This is because when imaging, unlike in visual, every jitter and jiggle matters. This is of course, of less significance when imaging the planets since your exposures (video, rather) will be generally short, usually far less than 1 sec
You've been imaging with a 50mm lens (and that's a great way to start!) which weighs next to nothing, so the CG-4 should handle that with ease.
At AT6RC, however, is (relatively) big and slow - meaning you'll need far longer exposure times. the Orion 8" is even bigger and heavier, although it does have a shorter focal length. I'm concerned that your mount will let you down or that the picture will be the victim of the slightest breeze.
Of your list, I think the wisest choice will be an 80mm as its relatively compact, light and reasonably fast. Do note you'll also need a field flattener thus for that reason you may want to may want to buy a quadruplet design, which already integrates the field flattener. (as stated above)
Although a small scope will reduce the resolution on planets, it will still give nice pictures and for added magnification you can use a barlow or tele-extender
Posted 05 December 2012 - 12:24 PM
Posted 05 December 2012 - 01:49 PM
Thanks for all the information, it is much appreciated.
Posted 05 December 2012 - 04:20 PM
Posted 06 December 2012 - 12:29 AM
Vixen GPDX Autostar mod
Meade DSI II
Posted 06 December 2012 - 01:32 AM
this scope will still be useful when you buy a bigger imaging scope later on for guiding or wide field pictures.
Posted 06 December 2012 - 02:09 AM
Posted 06 December 2012 - 03:21 AM
...they recommend starting with telephoto lens and a DSLR. After 15 years of astrophotography, I think that is the best way to start and learn what you are doing.
I have to disagree respectfully. A telephoto lens is great in that its usually much shorter in focal length than a "normal" telescope but most telephotos will exhibit field curvature wide open at maximal zoom (usually where you want to use it), fine focusing is usually an issue and there is no focus lock to ensure you didn't accidentally shift it. Also, you can't use filters, which are really useful in today's light polluted environment.
An AT65EDQ, on the other hand, has a perfectly flat field, better color correction than my reference telephoto (Nikon 70-200 f/2.8 ED) with a decent 2 speed focuser. At f/6.5 its only marginally slower than most consumer grade telephotos (e.g. the ubiqutous Nikon - or Canon - 70-300mm f/4.5-5.6 ED), costs about the same and can eventually be used as a guidescope or have one piggybacked to it with the included rings, which would have involved rather expensive adapters for a normal telephoto lens.
I think though that compared to most other scopes (doublets or triplets), a telephoto lens is a better beginning choice because most scopes will exhibit the field curvature anyway or you'll have to play with a flattener which has stringent spacing requirments.
Posted 06 December 2012 - 10:55 AM
Over on the DSLR forum there are a lot of nice photos from say the Nikon 180/2.8 ED IF. Stopped down to f/4 it is essentially perfect from corner to corner on APS-C.
Posted 06 December 2012 - 02:44 PM
I think I will end up going after a good used 80mm refractor or small APO. The ones you listed all had really good reviews too so will be keeping an eye out for those.
I do have a quite a bit of learned experience with the dslr and basic star imaging and timelapses (enough to fully understand ISO, Aperture, Exposure, Shutter Speed, etc). I also have a good telephoto lens (Canon EF 100-400mm f/4.5-5.6), but have yet to test it on the stars. Planning on trying it out on the 12th for the meteor show. Outside of that I do have a very cheap meade refractor (Ds2000 f8.8 90mm) and have a bit of experience imaging say the moon and a blurry Jupiter, just don't think the optics are there to do anything more (scope is also broken at one too many points).
P.S. tomcody: "The backyard Astronomer's Guide" has been on my christmas list (sister has hinted that it is a very good book)
Thanks again everyone
Posted 06 December 2012 - 10:15 PM
It's a great lens for that, I think. You might want to consider using it. At 400mm it is pretty much comparable to the Astro-Tech 65EDQ.
Posted 11 December 2012 - 10:33 AM