Multistar FWHM focus not working with CPWI driver

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lowenthalm
Posts: 143
Joined: Mon May 07, 2018 12:27 am

Multistar FWHM focus not working with CPWI driver

#1

Post by lowenthalm »

I am using CPWI on a CGX mount, controlling the Celstron mirror focuser through the mount. When I do a inward focus scan using a step of 5, it will step in take frames and plot it in the graph for several iterations maybe 5 to 10. It still hadn't reached the minimum of the star diameter when it suddenly Sharpcap reported in the log that "Focus scan seems to be moving away from best focus. Moving back to position 22295 and continuing scan". This position was wildly inward producing huge out of focus stars. No idea where it got the focus position from. I have had this happen every time I have tried to use multistar focusing.

I was using 1 second exposures on an ASI294 Pro cooled camera on an Celestron Edge 1100 when this occurred.

Previous version of Sharpcap from January (4.0.8629.0) does not have this issue. I have attached the log for you to review,
Attachments
Sharpcap focus scan.rtf
(165.82 KiB) Downloaded 21 times
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admin
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Re: Multistar FWHM focus not working with CPWI driver

#2

Post by admin »

Hi,

as a quick workaround, turn off the option to use 'smart scanning' in the focus scan options - shown below
Capture.JPG
Capture.JPG (54.32 KiB) Viewed 735 times
The idea of smart scanning is to automatically fix problems like scanning in the wrong direction or scans that stop a little short of best focus, however in your case it seems to be getting confused.

Helpfully, your log contains the measured positions and focus score values, so I can try to work out why those values are triggering an incorrect response from the smart scanning code and fix whatever is wrong.

thanks,

Robin
lowenthalm
Posts: 143
Joined: Mon May 07, 2018 12:27 am

Re: Multistar FWHM focus not working with CPWI driver

#3

Post by lowenthalm »

Aha! Thanks, I'll turn that off. I really didn't want to roll back my update to the latest Sharpcap version over just this. All the other features I currently use work ok.

The log has focuser position, and three FWHM samples taken during each focus step. The star diameters recorded in the log are consistently going down after each step before it suddenly goes rogue. Its hard to see how the data could have confused it, so some other subtle condition must have been involved. If there is any other info you need on the conditions under which this occurred, let me know. It happened to me every time I tried to use it, so I should be able to reproduce it for you at will if you need more extensive log data (I only snipped out the section of log around the focus event).
lowenthalm
Posts: 143
Joined: Mon May 07, 2018 12:27 am

Re: Multistar FWHM focus not working with CPWI driver

#4

Post by lowenthalm »

I saw this fixed in the next release, which I tested and it is indeed fixed - Thanks!.However, I have observed the same behavior on occasion in the Bahtinov mask inward autofocus where it will suddenly jump far inward just as its getting to the point where it seems to be just about to stop and move to best focus. It doesn't happen every time, just often enough to be annoying. This big step usually seems to be the last, and then it goes to best focus, but it includes the last far inward datapoint in the regression, so the best position point isn't very accurate when this occurs.
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Re: Multistar FWHM focus not working with CPWI driver

#5

Post by admin »

Hi,

if you could post a SharpCap log from one of the problem runs then I will have a look and see if I can work out what is going on.

cheers,

Robin
lowenthalm
Posts: 143
Joined: Mon May 07, 2018 12:27 am

Re: Multistar FWHM focus not working with CPWI driver

#6

Post by lowenthalm »

Captured an incident in Bahtinov mask focus. See attached log.
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Sharpcap log - Bahtinov mask inward scan with big step.rtf
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Re: Multistar FWHM focus not working with CPWI driver

#7

Post by admin »

Hi,

is your version of SharpCap 4 somewhat out-of-date? This looks very much like a bug I fixed about a month ago that affected scans moving in the negative direction only. If you are on an old version, give the very latest from the downloads page a try (may well be newer than the one offered by auto-update) - I think it will fix your issue.

thanks,

Robin
lowenthalm
Posts: 143
Joined: Mon May 07, 2018 12:27 am

Re: Multistar FWHM focus not working with CPWI driver

#8

Post by lowenthalm »

This occurred in the 4.0.9313.0 version from September 5th. It looks exactly like the bug I reported that occurred within the Multistar FWHM autofocus dialog box. That was fixed in the release above, but the similar bug in the Bahtinov autofocus routine was not fixed as of that release.
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Re: Multistar FWHM focus not working with CPWI driver

#9

Post by admin »

Hi,

OK, thanks for the info that the Bahtinov is still unfixed - I will investigate.

cheers,

Robin
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