Precise Star Focus : Bahtinov Masks

 

Bahtinov Focusing Mask Generator is at

http://astrojargon.net/MaskGenerator.aspx

Using Laser Printer and Copier Transparency Film, you can print 2-4 filters on a single A4 sheet !
Cost will be about 1$ for that !

Also contaction an On Line Laser Cutting Cie as customlasercutting in the US or sculpteo in France
you can ask for a Laser Cut filter and verify size on line.
For a filter 76 x 76 mm, 3mm thick black acrylic like described just below, it would cost max. 25$ a piece ...

 

Examples of HP LaserJet verified settings and results (output are .svg files to print directly from inside your navigator (IE, ...) :

 

Case 1 : Nikon 180 mm, 1:2.8 manual

Looking like this but don't use this image (low res) and print directly from .svg !!

I just made one on LP Transparency Film !

then an artificial star test at 100% size with SonyA7s and 180 ( (APS-C mode then F= 290 mm), f:2.8, 12800 ISO at 5 m distance :

 

Below, same enlarged 5x

Note : very easy to remove without touching it : just pull back the lens hood :)

Test on the real sky !

Bad (L) and good (R) focus on Vega (500%) :

Part of Lyra (50% of original RAW size), DSS with 5 frames, only light images :

Lyra, M57 (100%) ... Stars to about 12.5 Mag are detectable !

 

Case 2 : Nikon 50 mm, 1:2.8, manual

 

Looking like this but don't use this image (low res) and print directly from .svg !!

General use :

Main line not centered ... bad focus
Line centered ... Very good focus !!