Canon 550D and Maksutov-Cassegrain for asteroids?

[iamjulian]

Hello, I have a Canon 550D and am wondering whether something like a "cheap" Maksutov-Cassegrain on an EQ3/2 would be capable of taking the camera.  I am not interested in deep sky astro photography, I am simply after asteroids.  Currently using a barn door with a zoom lens but want to take it up a notch.  Already having a 12" scope, I don't really want another big one, so to get the 1500mm focal length that will give me (in theory) sub arc second pixel on the 550D, I was wondering whether the smaller form Maksutov-Cassegrain would be any good, or will f/12 mean I'd be unable to get anything but the bright magnitude asteroids without a really long exposure time?

I basically want to be able to image mag 12-14 asteroids with my 550D, without spending a fortune, but with more accuracy than I can get with a barn door.  Any advice greatly appreciated.  Thank you.

[baggywrinkle]

The main thing is whether you have the adapters to fix the camera to the OTA.

If you just think of the MK as a glorified telephoto lens you will not be far off. But it will not be a fast lens, so rather increase the ISO instead of the exposure time. That might make it more forgiving on an EQ3

As the 550D does not use a full size imaging sensor you can usually multiply the focal length by about 1.5x for the true FL of the MK as telephoto.

It would be worthwhile setting up in daylights to test the focus settings at a distant object.

[iamjulian]

Thank you.  Ah, so the crop factor is taken into account, I did not realise that.  I notice something like the Skymax 127 AZ GOTO can be had for less than kitting out an EQ2/3 with motor and polar scopes and probably way less fiddly in terms of getting adequate tracking.  Given that I'm not going to be stacking lots of frames for galaxies and stuff, maybe that would be adequate? 

If I know the camera, ISO, focal length, etc, how do I work out what kind of magnitude I could get to for a given exposure time - is there a calculator somewhere? 

I am interested in getting useful/usable astrometry on asteroids with my existing camera.  I understand I need to be getting around 2 arc seconds per pixel.