Flats with Grid Pattern?

[PRejto (Peter)]

Hello,

I'm seeing an odd looking problem on all of my flats using some older grear that has not been used for some time. The illumination is from a Gemini Snap-Cap at 5% brightness. The flat illustrated was 3 seconds 1x1 from a Moravian G2-8300 through astronomic Deep Sky filters and an ONAG XT.

The sample is from 30 frames created in CCDStack, bias subtracted. The individual flats also indicate a faint striation that has become enhanced through the master flat creation. All the flats, including ha, show this pattern but blue the least (with a longer exposure).

I suspect the Snap-Cap might be responsible but never noticed this in the past. I will take some flats using a different light source. In the meantime, has anyone seen something like this before?

Thanks,
Peter

[PRejto (Peter)]

I did further experiments....flats using a white sheet, longer exposures, etc and the grid pattern is in every sub.

Then I had a chance conversation with a friend still imaging with a KAF-8300 CCD and he confirmed the same in his flats and said it had no detectable effect on images.

So there it is I suppose. I used the camera so many years I've either not noticed back then or just plain forgot.

[gregbradley]

Do you subtract a bias from your flat?

I used to get grid patterns sometimes in bias images using a 694CCD. They would callibrate out usually (not always).

Greg.

[PRejto (Peter)]

Originally Posted by gregbradley

Do you subtract a bias from your flat?

I used to get grid patterns sometimes in bias images using a 694CCD. They would callibrate out usually (not always).

Greg.

Hi Greg! Yes, in my first post I said "bias subtracted." Also, tried without bias subtracted....same result.

I have some subs, but not enough yet for a decent image so I've been a bit lazy calibrating and using these flats. Hopefully not too much longer but of course the weather has changed for the worse (again).
P

[Ryderscope (Rodney)]

Originally Posted by PRejto

Hello,

I'm seeing an odd looking problem on all of my flats using some older grear that has not been used for some time. The illumination is from a Gemini Snap-Cap at 5% brightness. The flat illustrated was 3 seconds 1x1 from a Moravian G2-8300 through astronomic Deep Sky filters and an ONAG XT.

The sample is from 30 frames created in CCDStack, bias subtracted. The individual flats also indicate a faint striation that has become enhanced through the master flat creation. All the flats, including ha, show this pattern but blue the least (with a longer exposure).

I suspect the Snap-Cap might be responsible but never noticed this in the past. I will take some flats using a different light source. In the meantime, has anyone seen something like this before?

Thanks,
Peter

Hi Peter, problems with vertical banding in bias frames when using the QSI683 (which has the KAF8300 sensor) have been reported for some time. I am wondering if your flats issue could be coming from the same thing.

My QSI683 does suffer from this but the banding doesn’t make its way through the processing workflow so I don’t worry about it. I purchased my QSI camera in 2015 and I would have been using it for a couple of years before I noticed tha banding. I did do some research research at the time which indicated that a firmware upgrade was available and even went as far as downloading the new firmware. I didn’t install it though as there was a high probability of turning the camera into a brick so I left it. I’m on my iPad now so when I get back to my PC I will see if I can dust off the information that I have.

FWIW, here are a couple of links to some forum posts that discuss the vertical banding issue. May, or may not, be related to your problem but worth checking out all the same.

Cloudy nights

Star Gazers Lounge

Clear skies,
Rodney

[SB (Chris)]

Hi Peter
I get these patterns too. I found if you zoom in, the pattern disappears. It makes no difference to the image outcome I have found.

Chris

[PRejto (Peter)]

Thanks Chris and Rodney for your replies!

I'm not sure if the QSI issue is related to what I'm seeing. In that situation, if I'm correctly interpreting the posts, the banding appears in final images on the left side, though I do see similarities to what I'm seeing in the posted master bias/darks.

I guess I won't know if I've got a problem worth fussing over until I collect more data and continue processing! And then I need to ask if I'm motivated enough to invest more time in all of this as this camera is not my main camera and has been pressed back into use while my entire optical system is under repair/evaluation by Joshua Bunn due to a few wonky adapters.

Peter