PDA

View Full Version here: : Dobsonian and astrophotography


luka
12-04-2007, 02:13 PM
Hi everybody,
thanks for a great welcome yesterday - it has surpassed any other welcome I have ever seen on other forums :thumbsup:

I almost ordered my first telescope yesterday (8" Dobsonian) but after reading photography forums and few more webpages I have noticed that hardly anyone is using dobs for astrophotography so I am back to "not so sure what to get" again (astrophotography is what I am (mainly) interested in).

Is lack of tracking the only reason for dobs not being suitable for (deep sky) astrophotography? I have seen that quite a few people have built tracking platforms.
Is dob with a tracking platform a way to go or I am better off getting a refractor with equatorial mount?
I can afford only about $700-$800 :(

iceman
12-04-2007, 02:15 PM
:whistle:
Astrophotography with a dob (http://www.iceinspace.com.au/index.php?id=63,201,0,0,1,0)

:whistle:

Planetary Imaging and Image Processing (http://www.iceinspace.com.au/index.php?id=63,306,0,0,1,0)

:D

Having written the above, I would still say that if you're really interested in astrophotography, don't get a dob. Even with a tracking platform, you'll be limited to solar system photography.

What sort of astrophotography do you want to do? Planets/moon, or deep-space stuff?

luka
12-04-2007, 02:40 PM
Deep space stuff.

So far I have taken a few photos of the Moon, Orion nebula and LMC with my DSLR on a tripod and have some experience stacking them with Deepsky Stacker, Registax and Iris so I thought that I am ready for the real thing...

In one of the other forums I have seen people suggesting Orion ED80 with EQ5/6 mount but it is a bit over my budget. I could afford the scope but not the mount :-(
Hence the attraction of a dob...

iceman
12-04-2007, 02:46 PM
Unfortunately astrophotography, especially deep space stuff, can be expensive. An ED80 on a HEQ5 or EQ6 should really be the minimum if you want to get serious about it. That's way over your budget though.

The dobsonian on the tracking platform really won't do what you want:
1) The tracking won't be accurate enough
2) The DSLR won't come to focus without moving the mirror up the tube
3) The price of the dob + tracking platform is still over your $800 budget.

If astrophotography is really what you want, you'll really need to save some more and start with a budget of $2k or so.

I've used a DSLR on a tripod on top of an EQ platform, which can work well for wide field/low focal length stuff, as you have done on a fixed tripod. But as soon as you start using a longer lens or sticking the DSLR in the dobsonian, the accuracy of the tracking becomes the #1 factor. It just won't be accurate enough for long exposures without drifting. Believe me, i've tried.

I had a 10" dob on an EQ platform and it was great for solar system stuff, but just didn't cut it for deep-space stuff.
I now have a 12" newt on an EQ6 for planetary imaging, but I'll use an ED80 on the EQ6 for deep-space stuff when I can afford an ED80 plus rings + ...

luka
12-04-2007, 03:06 PM
How about taking many short exposures and stacking them? That should reduce the need for the accuracy of the tracking.

I have seen that "deep-space people" make, for example, 5 x 5min exposures - this should be equivalent to, for example, 150 x 10sec exposures? It would be a real pain to take photos and stack them all (I have done 200 x 5sec exposures) but it should work even with a dob?
Or am I missing something important here.

ving
12-04-2007, 03:13 PM
like mike said. although most short tube refractors used are of the ed80 type I have seen smaller scopes yet used, but the smaller the scope the longer the exposure needed. what you could do is buy an 8" or 10" dob and save up for the mount. an eq6 will handle both of them (not together obviously) and be quite stable.
I originally bought a 8" dob and it is now mounted on an heq5 (not to be confused with an eq5) which is about the limit for the mount. its fine for planets though and i could probably do DSOs too but thats not my bag :)
whatever you choose enjoy :)

ps: dont forget the cost of the camera and mounting equipment on top of the other costs...

davewaldo
12-04-2007, 03:55 PM
Hi Luka and welcome.

About 8 months ago I was in the same situation you find yourself in now. Which scope to get... and being interested in astro imaging.

Well to cut a long story short I bought a 10" GSO Dob. I realised that for my budget (also around $800) I would not come close to getting into imaging in a good way.

As Ving has sugested you could buy an 8" dob which would be GREAT for visual use and then save up for the mount later. The mount is where you need to spend the money in imaging, not the scope (when starting at least).

I wouldn't be surprised if it would cost $800 just for all the accesories to setup for astro imaging... rings, adapters, guiding camera, batteries etc etc

I considered buying an ED80 first and then buying a mount later but there is not much to be seen visually through an 80mm refractor, and so I would have probably lost heart. My experience with my dob has given me many amazing views and had totally got me hooked!

My plan now is to buy an EQ6 when money permits so I can start imaging.

The reason I recomended the 8" dob is that if you plan to mount it later down the track on an EQ mount, any of the cheaper mounts (EQ5 or 6) will handle a 8" much easier than a 10 or 12".

Well this is my take on a similar situation.

Enjoy!

Dave.

luka
12-04-2007, 05:37 PM
Thank you very much guys, you have clarified quite a few things and made my decision much easier. Get a dob now :D and save up for a mount.
As Dave summarised it nicely, my budget does not allow me to do any serious imaging (yet).

Another question, I was not aware that (H)EQ5 or EQ6 would take an 8" dob. Is the limitation just the weight?
The reason I am asking is that EQ5 can take 10kg and the 8" dob that I was looking at is 9.4kg. I know that this is close but EQ5 is almost half the price of HEQ5 which means that I could get the money for it in half the time.

rmcpb
12-04-2007, 07:00 PM
If you have an 8" dob and want to get into deep sky photography then an EQ6 is the mount for you.

Lee
12-04-2007, 08:26 PM
Welcome!

You will find that 5x5min is not nearly the same as 150x10sec - the 5x5 will show a lot more depth. I think even a 5 sec exposure at a deep sky object through a Dob will trail badly.
Dobs have their advantages - just none of them are photographic advantages unfortunately!