Svbony 405cc vignetting

[Jonathancilia]

Hi, recently upgraded to the svbony sv405cc with an IMX294 sensor from a zwo asi178mc camera and its very sensitive to deepsky which is great but i have noticed that it has a vignetting issue, like the one in the picture no matter how you stretch the levels the white ball remains visible and if it goes away the galaxy details go with it. What causes this? I havent used the camera cooler yet. I live in a bortle 7 area, im using a skywatcher 6 inch virtuoso collapsible dobsonian which i made a shroud for it to avoid light leaks and even surround the telescope with a big box to block out light pollution

Screenshot_20230413_002454_Gallery.jpg (254.18 KiB) Viewed 10587 times

[Jonathancilia]

Screenshot_20230413_004915_Gallery.jpg (370.66 KiB) Viewed 10586 times

[admin]

Hi,

the most likely cause is that the telescope is not fully illuminating the larger sensor of the SV405, meaning that the edges and corners get a lower amount of illumination than the center. This is simply a matter of the geometry of the internal structure of the telescope which means that for the parts of the sensor further away from the center, light from parts of the aperture just cannot get to the sensor.

The usual fix for this is to use flat frame correction - you create a flat frame by applying even illumination over the telescope aperture. The flat frame records how much the dimming is in different parts of the image, then SharpCap (or another processing application) corrects the actual images for this dimming effect.

Check out the documentation on flat frames in SharpCap here : https://docs.sharpcap.co.uk/4.0/#Captur ... t%20Frames
Although it talks mostly in terms of reducing dust shadows, it will fix vignitting just as well.

Note that flat frames do not eliminate vignetting completely, but can reduce it by a large fraction (99% or more if used well). If you stretch the image enough then you will still see some vignetting though.

cheers,

Robin

[Jonathancilia]

Thank you for the reply, this was with no darks applied. With this camera im a bit confused because there are 2 mpdes in which it can work, one of them is under the "direct show" section and the other above it. One of them has the gamma option and the direct show one has the brightness setting instead. I still have to get thr settings right as its a bit different than the zwo camera, with darks the vignetting was greatly reduced but i have to mention that i dont know if i did the settings right for the darks, this is the image that was with the darks applied of about 10 mins exposure

The settings were:

8 second exposure
350Gain
Contrast 50
Black level 0
Gamma 0.5

Untitled2.png (237.93 KiB) Viewed 10570 times

[Jonathancilia]

IMG_20230413_085526_893.jpg (103.93 KiB) Viewed 10570 times

This is the unedited picture straight out of the livestack

[admin]

Hi,

normally you should use the camera from the 'SVBony' section of the cameras menu, not the 'DirectShow'. By using DirectShow you miss out on the advanced features of the camera (high bit depth, cooling, etc). You will get more control over the camera with the 'SVBony Cameras' option, but some of the controls may have different names.

I wouldn't expect dark subtraction to have much effect on the vignetting you were seeing, but it's possible that it is just being masked in the later images because you used different settings for the stretching of the image (which have resulted in a fairly black background) - ie, you have just made the background in the center darker due to different settings, stopping the vignetting from showing.

It's all a gradual learning curve, and you are doing pretty well so far to get those images, so just keep at it and try a few new things each time.

cheers,

Robin

[Jonathancilia]

Thankyou and to your amazing software that i am able to do this i need to retry in proper clear skies because last time the skies were abit hazy aswell and messed with the colours

[Jonathancilia]

The vignetting issue ended up being light leaks inside the OTA, since my tube is collapsible its really hard to seal it completely, most leaks were from the back of primary mirror, now i used it a couple nights and the vignetting went away with adjusting the histogram well here are some results

Screenshot_20230423_100353_Lightroom.jpg (833.41 KiB) Viewed 10532 times

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Screenshot_20230422_225206_Lightroom.jpg (86.88 KiB) Viewed 10532 times

[admin]

Hi,

well done on finding the cause and on getting some really very nice images! I must admit I've never had to deal with light leaks in that sort of situation before, so it didn't even occur to me.

cheers,

Robin

[Jonathancilia]

Thank you im so happy having some amazing nights out stargazing