Ok I thought you might have had the wedge on. Then definately field rotation. The longer your focal length the quicker rotation starts up. The further way from 0 dec you get the quicker you'll get field rotation when fork mounted. Though ironically the worst is right on the meridian at 0 dec. If you look at how your fork mounts work you'll see why. There are other areas of the sky that you may also get a bit longer but I can't remember where
Check out this link (infact check out the whole site, its a good one)
http://www.allaboutastro.com/Article...drotation.html for details about field rotation
Try the 3200 but I think you'll find it really noisy