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Focus Assist Problem
Posted: Wed Jan 17, 2018 7:54 pm
by Luling_Skies
I'm running the new 3.1.4944 beta version on my HP Omen laptop with my ZWO ASI071MC-Pro camera. I previously used Sharpcap version 3.0.4008.0 and in particular its focus assist with the Bahtinov mask tool. I find on the new beta version the program fails to find the star spikes, see attached screen shot. Any changes in the Bahtinov mask coding?
Tim
- focus capture.JPG (156.28 KiB) Viewed 3066 times
Re: Focus Assist Problem
Posted: Wed Jan 17, 2018 10:33 pm
by admin
Hi,
I think that you've been bitten by a bug in 4944 where the selection area rectangle is not being drawn - this is fixed in 3.1.4949. I expect that the (invisible) selection rectangle wasn't around your star. Sorry about that!
cheers,
Robin
Re: Focus Assist Problem
Posted: Thu Jan 18, 2018 7:07 pm
by Luling_Skies
Thanks for the prompt replay. I have installed version 4949 and will try it out probably tonight and let you know if the issue is resolved.
Regards,
Tim
Re: Focus Assist Problem
Posted: Fri Jan 19, 2018 3:27 pm
by Luling_Skies
Robin,
I tried the focus assist again last night with the 3.1.4949 version and it reported it found the diffraction lines from the Bahtinov mask. Here was my view without the tool engaged. The spikes are centered well so I should be close to optimum focus.
- visual focus.JPG (105.22 KiB) Viewed 3031 times
Then I engage the focus assist and it gave the report below. What gives me pause about the numerical calculation of focus is that the projected lines by the program do not align well with the diffraction spikes from the mask.
- sharpcap focus.JPG (157.77 KiB) Viewed 3031 times
Any ideas on why the lines don't align? Are the calculated focus results valid?
Regards,
Tim
Re: Focus Assist Problem
Posted: Fri Jan 19, 2018 7:40 pm
by admin
Hi Tim,
so I tried loading your image above into the deep sky test camera and turned on the Bahtinov function. I can make it detect correctly subject to a couple of changes
1) Turn up the black level - you see the area excluded from the calculation because it is below the black level as it is shaded in red. You want this to be a loose fit around the bright area as shown below.
2) Brighten the image (by setting a 2s exposure with the test camera - you would need to increase gain or exposure).
- Capture.PNG (276.23 KiB) Viewed 3026 times
Perhaps having a digital gain in here might help in a future version, but hopefully the ideas above will get you going.
Robin
Re: Focus Assist Problem
Posted: Fri Jan 19, 2018 10:04 pm
by Luling_Skies
Thanks Robin. I'll give it a go next observing session.
Regards,
Tim