3 replies to this topic

[Whereisclearsky]

Hi,

 

I have found 2 bahtinov masks projects for 3d printing but they are all for 60mm, mine is going to be 50mm.

 

I wonder if anyone has a project for 50mm?

I know nothing about 3d printing but my friend has a printer.

 

Thanks!

[triplemon]

The exact Bahtinov pattern size is not relevant for its function - within wide limits. So any mask from at least 40 to 70mm will work the same with a 50mms scope.

But, why do you want to precision focus a guide scope ?

 

A faint star has poor SNR and isn't suitable for guiding.

A bright star can have whatever aberation it wants, the guiding algorithm will only guide on its centroid. For many reasons - discrete pixels etc. In some cases defocus is outright required to reach sub-pixel accuracy, as this requires the star to stretch across multiple pixels.

Edited by triplemon, 21 March 2025 - 09:17 PM.

[Whereisclearsky]

The exact Bahtinov pattern size is not relevant for its function - within wide limits. So any mask from at least 40 to 70mm will work the same with a 50mms scope.

But, why do you want to precision focus a guide scope ?

 

A faint star has poor SNR and isn't suitable for guiding.

A bright star can have whatever aberation it wants, the guiding algorithm will only guide on its centroid. For many reasons - discrete pixels etc. In some cases defocus is outright required to reach sub-pixel accuracy, as this requires the star to stretch across multiple pixels.

I've seen a post from PHD developer saying that with newer versions you want best focus, in past some people recommended having it slightly out of focus.

 

So I don't know anymore.

[triplemon]

Just focus for minimal star size using the preview image in phd then. No need noir benefit for any precision focus. Unless focusing is a separate hobby of yours.