Focus mask for large Dob

[oldfruit]

Hello,

I am wondering if anyone could advise where where i could source a focus mask for a 20 inch dobsonian telescope please?

[almcl]

If you can't find a supplier of a ready made one, it might be worth using one of the on-line Bahtinov generator programs to produce a suitably sized one and then submit it to one of the laser cutting services?  I did this some years ago for my 8" and used black acrylic but for 20" perhaps aluminium or even thin steel might be more appropriate.  

Might also be worth cutting one out of cardboard using the generated pattern to make sure it works OK before investing in the real thing?

Edited November 26, 2021 by almcl

[Peter Drew]

I made one for my 30" out of thin aluminium sheet, three holes provided me with a choice of 12" F10, 10" F12 and 8" F15 pseudo apochromats.        🙂

[Xilman]

On 26/11/2021 at 12:43, almcl said:

If you can't find a supplier of a ready made one, it might be worth using one of the on-line Bahtinov generator programs to produce a suitably sized one and then submit it to one of the laser cutting services?  I did this some years ago for my 8" and used black acrylic but for 20" perhaps aluminium or even thin steel might be more appropriate.  

Might also be worth cutting one out of cardboard using the generated pattern to make sure it works OK before investing in the real thing?

I made one out of cardboard for my 40cm using a design from one of the on-line resources. It works so well that I haven't spent any money on a more robust version.

I confess: I never thought that I would rule an optical diffraction grating with a craft knife!

[Peter Drew]

Just re-read this thread and realised it was a different type of mask enquiry.  still worth making an aperture mask for a large scope.    🙂