I was trying to work out which combination of scope and camera sensor and Focal reducer gave what sort of Field of View, ie, what's best for small nebs, big ones, galaxies, wide field, etc.
I was going to post a question on IIS, but got a little energetic and did a few searches here first. There were some recommendations for CCDCalc.
http://www.newastro.com/book_new/camera_app.php
It's a brilliant little program that's free, and let's you keep a list of your own scopes and CCD's and then shows you what FOV you get on a range of DSO's, including piccies that you add. Make sure you download it!
BTW, if you go into the CCDCalc program directory (normally c:\program files\ccdcalc\), find a file called "camera_data.dat", make a backup copy then edit it to remove the endless list of cameras you don't have
Quicker than deleting them one by one in the main program.
Unfortunately there's no file for scopes, so you have to do them from the main program.
Cheers,