A wide strip in the center of the Sun : how to avoid it?

[Manon]

My equipment is a Lunt TS40THa refractor, filter B-600. With two different cameras, I get the same problem most of the time : a wide strip crossing the whole solar disc at the center (see attachment). With my ASI224 MC, the strip is green and with my ASI120 mono, the strip is dark grey. I can also get images of the Sun with no strip but I can't find the reason why sometimes it is there and sometimes not. My captures are done in .ser format and mono 16.
SInce the problem occurs while using different cameras, I believe that this happens when I use SharpCap (format? exposure?... Thanks for your help!

17_36_16_lapl6_ap169_conv.jpg (29.71 KiB) Viewed 3313 times

[admin]

Hi,

I think the first thing to do would be to set all the camera settings back to default in case SharpCap is restoring the previous settings (perhaps including dark/flat frames) and those are causing the problem. You can do this easily by holding down the CTRL key while opening the camera. Also turn off any processing stages in SharpCap (planetary live stacking, Display FX, etc) so that you are seeing the raw image from the camera onscreen in SharpCap to see if the artifact is in that image.

If none of that helps, see what happens when you rotate the camera in the telescope. If the dark band remains in the same orientation of up/down then it must be coming from the camera or software. If it rotates to a different orientation then it must be an optical effect coming from the telescope. It would also be worth trying an alternative capture application at this point - if the effect vanishes in the alternative application then it is something in SharpCap causing it (or at very least the camera configuration that SharpCap is setting up). If it stays visible in the other application then it is most likely an issue coming from the camera hardware or driver.

cheers,

Robin

[Manon]

Hello Robin,
Thank you so much for your explanations. Sorry if I didn't reply earlier: I needed some sunny sky rather than cloudy in order to apply your recommandations.
In the meantime I downloaded SharpCap version 4.1.13332, 64 bit, hoping this would solve my problem. So far, nothing really worked and I didn't try another capture application yet.
With the ASI120 Mono, as I reduce the Gain, (from 56 to 31 for instance) the strip gets paler. But with the ASI224MC, at Gain 225, there's no strip and at Gain 178, there is a green one! So reducing the Gain might have an effect on the strip boldness, but it is not conclusive to me.
Tonight I ordered a new camera, the Player One Neptune M (mono), hoping it will work better!

Let's wait for the results. If this was the solution, I surely will share it on that forum.
Clear skies,
Manon

[admin]

Hi Manon,

I am still wondering about incorrect flat correction or dark subtraction causing the issue. If you go and look at the capture files created by SharpCap, each of them will have a 'capturesettings.txt' file next to it that records the various camera/processing settings in use at the time of the capture. Have a look in some of those using Windows notepad (or some other text editor) and see what settings were in use. In particular, check that 'Apply Flat' and 'Subtract Dark' are both set to None.

Feel free to post one of the capture settings files here so that I can check in more detail.

thanks,

Robin

[Manon]

Hello again Robin,
I checked every captures I did since I started using SharpCap and in all cases, including perfect captures as well as captures with the band in the middle, "Apply Flat" and "Sustract Dark" are all set to None.
To tell you the truth, I didn't even start doing flats and darks... I'm brand new with solar imaging!

[Manon]

Problem solved! Nothing to do with SharpCap or camera or flat : the problems comes from Autostakkert!4. In this software, go to Image Calibration, then Column Noise Correction. If this item is enabled, then disable it and try again. In my case, it worked instantly. No more vertical stripes!

Thanks anyway Robin for your replies.
Cheers!

[admin]

Hi,

thanks for sharing - it might help someone else who runs into the same sort of problem

clear skies!

Robin