Bahtinov Mask

[ColHut (Colin)]

How many of you fellows use them for visual use? I was wondering as I have sometimes difficulty getting good focus on the moon and wondered if I get proper focus on a small star it should be right despite the seeing for the moon?

cheers

[mithrandir (Andrew)]

Since for all practical purposes when it comes to focusing the Moon and stars are at infinity, using a star will be fine. The Moon and planets are too big and bright and the diffraction spikes are indistinct.

[Benno85 (Ben)]

Originally Posted by mithrandir

Since for all practical purposes when it comes to focusing the Moon and stars are at infinity, using a star will be fine. The Moon and planets are too big and bright and the diffraction spikes are indistinct.

Apologies on a stuuuuuupid question, but does that mean that one could use the mask and achieve focus on, say, Sirius, and then to M42 and commence imaging without the need for refocusing?

[Geoff45 (Geoff)]

Originally Posted by Benno85

Apologies on a stuuuuuupid question, but does that mean that one could use the mask and achieve focus on, say, Sirius, and then to M42 and commence imaging without the need for refocusing?

In theory "yes". In practice, you may get mirror movement in a reflector as you go from one part of the sky to another. You'd be pretty safe doing it with a refractor.
Geoff

[Benno85 (Ben)]

Cheers Geoff, I'd be using a refractor so you've put my mind at ease