SharpCap Forums

Thanks Chuckwagon (can I call you Chuck?) and Menno.

OK, I did actually generate the mask I am using based on the specs for my scope. However, it never occurred to me that if I change the focal length, I would need a new mask. I just went back to the Thingiverse page and now see that the spacing between the slots changes quite a bit with changing FL (I assume it uses the same formulas used on the link Chuck sent). It does seem to work at the three FL I use (450, 900, and 2700mm). At least it generates the typical pattern and I can move the center spike.

At any rate, I can use the mask I have now to set the focus at 900mm and see if there is still a difference between what I set by eye and what the tool tells me. I don't think I have sensor tilt based on other images I have taken, but will also look more closely for that.

Thanks!

UPDATE:
I went out last night in order to test the Bahtinov focus tool with my sensor at the 900mm FL to see if there was any difference. Short answer, NO. I am still seeing differences between what 'looks' like a good pattern and what SC chooses. I did test the results of each using FWHM and the difference was lost in the noise so to speak. That is, the measurement varied over time by more than the any difference I could detect. However, based on the input from Menno, I am convinced that my eyes are deceiving me in this case, and I can trust the tool.

Thanks for the help! Robin, you can consider this closed.

P.S. Although Bahtinov masks are customized to various focal lengths, my 900mm-based mask seems to work fine at other focal lengths. From the little I have read, it may be that the energy in the spikes could be better with an optimized mask, but the functionality of the pattern is retained.

Hi,

thanks for the report - glad that you are happy now.

I must admit that I have considered that bahtinov masks are maybe not the ideal mask for camera based focusing - they are designed to make a pattern that is obvious to the eye, but that can be a problem for software to interpret it... A more suitable mask would leave less brightness in the central spot and put more into the spikes (if such a thing is possible).

cheers,

Robin