Focusing for planetary

[RobF (Rob)]

Hi. Just wondering what people do for focusing on planets for webcam imaging? Is a Bhatinov on a bright star any use, or better to focus on the planet's limb or a moon?

I expect if seeing is average you would want to be tweaking focus between each run?

Close to getting Peter's old motorised focuser working on the Newt, so thought I'd find out what the experts do.

[mithrandir (Andrew)]

A Bahtinov mask on a star works fine for planetary work. Planets are too large and you don't get clean spikes.

Both the stars and planets are so far away that for focusing they are effectively both at infinity.