I am considering purchasing an EQ platform for my dob for astrophotography (5 minute exposures or so). Can anyone give me advice on which one is best?

I am looking for exposures at least 3 minutes at a time. Easy assembly. Hand controller and/or pc controlled. Able to track off axis objects (like comets).

Not wanting to spend $700 or more....any kits available???

I'm not aware of anything (kit or fully assembled) in that price range with the accuracy required to give you good photographic results over five minutes with any kind of focal length. If your dob is over 1,200mm focal length you're going to be pushing the limits with a standard platform.

You will need a way to guide or autoguide the platform. Some designs, like Tom Osypowski's, can be driven and/or guided ... but the controller, motors, and encoders alone will consume your budget.

If you are good with electronics, you might be able to build your own following someone's design, but I'm not aware of such plans being freely available. There probably are some online.

JMI's platforms for dobs up to 10" were released at a price of about $599, if I remember correctly ... but I do not think they were advertised as guidable.

I think the ServoCat/Argo Navis setups can track comets and asteroids, with the proper downloads, but they're considerably more expensive and only include the electronics. I am not greatly impressed by these setups. They certainly do work, but they're rather fragile, relying on pulleys and cables. The clutch arrangements on the ServoCat can be damaged if you forget to disable them and slew the scope by hand (a logical mistake for long-time dob users accustomed to guiding by hand). I have used such a system with a 30-inch Obsession (it's quite heavy) and it works very well as long as you're careful with it. But I wouldn't attempt to use it for astrophotography.

They cost far more than your budget allows but these equatorial platforms are certainly capable of being used for imaging.

See http://www.equatorialplatforms.com/images.html for information on the dual axis platform.

Dave Mitsky

I see. Well, I will have to lower the exposure times and stack them. I shouldn't have to go too terribly high on power for DSO's. And the round table platforms as well as many others do advertise shorter exposure length astrophotography (up to 10 minutes). Hmmm, I will need to do more homework on this. Thank you both for your inputs Jeff and Dave.  

Equatorial platforms work well for visual observing and very limited astrophotography applications.  It's already been mentioned that you'll quickly exceed the tracking capability of a platform as you move into higher magnification or longer duration astrophotography.  If you intend to get deeply involved with Dob astrophotography, you truly might want to consider stepping up to one of the systems designed for this application.  ServoCat has already been mentioned.  There are also the Tech2000 Dob Driver and the Mel Bartel's homebrew systems.  There are others, but these systems have been around for a good while and are known to work well.  If you decide to go in this direction, make sure that the system you select has an autoguide feature.  As you skill in astrophotography progresses, you'll want this capability.

For the record, I have no commercial interest in selling equatorial platforms.  Here are some web sites with DSO astrophotographs and images that, IMO, hardly seem "limited" that were captured using Dobs mounted on equatorial platforms. 

http://www.equatorialplatforms.com/del.htm

http://www.equatorialplatforms.com/osypowski.htm

http://www.equatorialplatforms.com/askew.html

http://www.robertbrunck.com/Bob-Web-Pages/Astrophotos-01.html

Dave Mitsky

If you have the time and inclination, you might want to consider building one.  Neither the easiest nor the most daunting of projects, but it will make you "one with your telescope".  Here's a link to the ATM page showing a list of "how to" site.  You'll need to scroll down a bit.  http://www.saao.ac.za/~wpk/atm.html