Tips and tricks for getting good focus with CCD?

[chd]

Does anyone have helpful hints for getting good focus with a CCD? I took a series of images last night that I thought were okay but then turned out not to be quite in focus when I started working on them... :/

The approach I've used to date has been to do continuous 1 second exposures and try to adjust focus for the smallest FWHM value. The numbers jump around a lot even when I'm not touching anything though, because of the seeing I assume, but that makes it a little hard to dial in.

There must be some amount of play in the focus mechanism, so is it better to approach the focus point from the infinity end, or from the near end? (This with a Celestron SCT.)

Thanks!

[grimble61]

Hi chd

you really need to up the exposures to around 3 seconds to even out the seeing, i use 5 second exposures with a mask and get good focus.

regards

graham

[chd]

Ok, will try that - thanks!