New Feature : Improved Star detection in Multi-star FWHM Focus

Discussions, Bug Reports and Issues related to Beta versions of SharpCap
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Re: New Feature : Improved Star detection in Multi-star FWHM Focus

#21

Post by admin »

Hi,

yes, they could give similar readings in those situations (or at least in less extreme versions of that). One thing to be aware of though is that the actual selection of which stars to investigate does have a filter that will reject long thin blobs - it prefers circular ones. It's not a particularly strong filter - a 4x1 star would probably just sneak in, but a 5x1 (or anything with an aspect ratio of 5:1 or higher) would be excluded.

cheers,

Robin
Anthony Quintile
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Re: New Feature : Improved Star detection in Multi-star FWHM Focus

#22

Post by Anthony Quintile »

Robin-

Thanks for the answer. I'm not sure that this is, in fact, entirely relevant to my issue, but at least I know it could be part of the solution.

-A
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Re: New Feature : Improved Star detection in Multi-star FWHM Focus

#23

Post by umasscrew39 »

Hi Robin

I am still struggling with this method when using NB filters. Last night I used my Chroma Ha 5nm filter (bright moon but good seeing) with my ASI2600MM on an 80mm scope. My typical camera settings are a gain of 100 and offset of 50 and I take 300s subs. To focus, I kept these camera settings but used a 10s exposure. It was picking up only about 10-11 stars and it struggled to produce a nice curve. The detection settings were at default: sensitivity was 96; max brightness was 98; noise reduction was 1.50 and both suppress hot pixels and use display stretch were checked). I get similar results with the ASI6200MM on the C11". I have no issues using BB filters. I do not want to increase the exposure time any longer. Other then increasing the gain, I am not sure what else to try. Any obvious thing I am doing wrong or further suggestions as to what to try?

Bruce
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Re: New Feature : Improved Star detection in Multi-star FWHM Focus

#24

Post by admin »

Hi Bruce,

try this...

* make sure the 'Use Display Stretch' option is ticked just above the sensitivity adjustment.
* Use the display stretch controls (right hand side) to brighten the image to make stars more visible - just clicking the lightning bolt auto stretch button should be enough to do this.

This approach can be very effective at helping the focus routines find fainter stars that are normally ignored.

cheers,

Robin
Mike Hooper
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Re: New Feature : Improved Star detection in Multi-star FWHM Focus

#25

Post by Mike Hooper »

Hi,
I have been successfully using this tool for several months to focus on stars in the same field of view as a DSO prior to Live Stacking. However, on my last imaging session I had trouble with the tool and yet I am not aware that I changed any settings in SharpCap (black level, noise, etc.) or indeed camera settings (exposure time, gain, set temperature). I could clearly see a good number of quite well focused and not overly bright or faint stars on my monitor and just wanted to check and improve focus a little. When I clicked on multi-star FWHM focus the message displayed was "no stars". In previous sessions a number of stars (20 or so) had boxes around them and the FWHM measuring began spontaneously when I clicked on the FWHM Focus option. In the latest session I was able to perform FWHM measurements on some individual stars, although often stars were rejected when I tried constructing the focus button around them as being too bright / saturated.

Probably there is not enough information to give a diagnosis of my problem, but if you have any advice I would be very grateful to receive it, thank you.

Mike Hooper
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Re: New Feature : Improved Star detection in Multi-star FWHM Focus

#26

Post by admin »

Hi Mike,

I'm going to take a guess - maybe you had previously used the display stretch function to bring out the visibility of something faint. If that is left on then the stars can look well exposed on screen when in fact they are very faint in the raw, unstretched image. This can cause the sort of problem you are describing.

Is that a possibility?

cheers,

Robin
Mike Hooper
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Re: New Feature : Improved Star detection in Multi-star FWHM Focus

#27

Post by Mike Hooper »

Hi Robin,
thank you for your last reply. I had another go a few nights ago and although I still didn't note the exact settings in Multi-star FWHM I found that when using my mono camera (ASI294MMPro) that the focus routine was able to detect plenty of stars when I had a luminance filter, but it failed for each of the RGB filters ("no stars), even though stars were clearly visible in the image in live view. I did not change any settings including auto-stretch. Interestingly despite not being able to detect any stars live stacking worked well (having performed a visual focus) for the RGB as well as the L filters and I was able to monitor the FWHM graph in the Filter (FWHM) tab in live stacking.

Probably unless I try to play with sensitivity and auto-stretch I won't be sure if I have a real problem or not?

Kind regards,

Mike
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Re: New Feature : Improved Star detection in Multi-star FWHM Focus

#28

Post by admin »

Hi Mike,

that's very odd - I can't quite see how the colour filter would have such a big effect - basically it should just make things about 3 times dimmer, which is easily compensated with gain/exposure tweaks.

If you have a chance, please save a 'working' image and a few 'not working' images into FITS format using the 'Snapshot' button in SharpCap and share them with me. Ideally with a screenshot showing the non working situation so I can see the camera settings, FWHM star settings, etc. Then I can try to reproduce what is going on and hopefully understand the issue.

The FITS files will be too large to share here, so I would suggest uploading them to GoogleDrive/OneDrive/Dropbox/etc and then sharing a link here to download them.

thanks,

Robin
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