profdann

Ooh, thanks, I'll try to remember this in four months time when the skies are clear again!

If it wasn't for the fact that DSS takes 12 hours to stack the images, and that I can't use any other method than just the standard average (no Kappa-Sigma satellite trail removal for me!) because it takes too much disk space during the stacking process, 5 second exposures would actually be quite nice!

Yes, that's it - the azimuth tracking seems to be dead on all night, but the altitude has a huge error causing the object to drift more than half way out of frame over about 10 minutes before returning to the centre. It seems to be fairly periodic, but I don't think the SE mount allows that to be corrected. Pointing near to Polaris means that the object isn't moving very fast, so the error occurs over a longer time period, so the star trails are smaller. I've thankfully been saved from this discovery by the fact that the camera hits the mount at anything above 65 degrees altitude! This is a crop of one of the worse 5 second exposures, the camera was tilted by this point so the trails are in the altitude direction and it's from the centre of the frame, so probably not field rotation.

Thanks! The nice part about using 5 second exposures is that you can rack up a huge number of subs, I think I was getting 450 an hour! Also the keep rate was actually 97% which was a nice change. It kind of hurts to almost double the shutter count on the camera overnight, but I'm looking into shorter focal length scopes so that I can increase the exposure time. This thread just goes to show that it's definitely worth having a go - field rotation will be the least of my issues for quite some time!

After seeing some of the images people were getting with Alt-Az mounts, I decided to give it a go with the Celestron 8SE, the long focal length makes it quite difficult, but also makes it very useful for going after the smaller objects e.g. planetary nebulae, smaller galaxies, so long as they are bright enough! I'm able to get 30s exposures when the object is close to polaris, e.g. M81, but for anything else, only 5-10 seconds is all I can do! Here's the ring nebula from a week ago, taken with a Nikon D610 through an 8SE at f/10. It's made of 1719x5s (!) exposures at ISO 6400 (So that DSS can see the stars) - only 2 and a half hours of data, but 60GB of files. Not the most efficient way of doing things, but it's a start.