Soo hard to get the right info, feeling frustrated is an understatement !

[themos]

I'd be very surprised if we go ahead with tonight's planned observing session, given the weather. Check that AAS blog site, it gets updated aorund 6:30pm with a message saying whether the observing will go ahead or not.  if we do, it will be at Bury Down

 (map http://www.abingdonastro.org.uk/aas_blog/?page_id=27  ). I will not be going today, in any case, as it's my daughter's 17th birthday. 

[dph1nm]

You can use the mount if you wish, but for long exposure imaging (where long is probably not much more than a handful of seconds with even a moderate focal length) you also need to rotate the camera

The amount of field rotation is the same at any focal length on an alt-az mount. It just depends on position in the sky. Straight up is bad, E or W horizon is very good. Basically you can nearly always get 30secs, and sometime 1-2 mins before rotation becomes noticeable.

Having said that, if you just want to use a camera (not telescope) then I vote for the Ioptron Skytracker.

NigelM

[JamesF]

The amount of field rotation is the same at any focal length on an alt-az mount. It just depends on position in the sky. Straight up is bad, E or W horizon is very good. Basically you can nearly always get 30secs, and sometime 1-2 mins before rotation becomes noticeable.

The amount is the same in terms of the amount of rotation, but surely it is different in terms of its effect on the imaging sensor depending on the focal length?

If you're imaging at a focal length giving 10 arcseonds per pixel at the focal plane and the target has moved four arcseconds you may not care at all, whereas you may well if your focal length gives 2 arcseconds per pixel.

No?

James