QHY183C Gain 0 Performance - Forums

Topic starter

Mar 12, 2022

Hallo to all,

i have purchased the QHY183c and this is the result of the First Light two days ago. Telescope is the TS UNC Newton 200/4. 450 lights with 46 seconds Gain 0, Offset 12, 50 Flats and Dark/Flats and 100 Darks. I used Sharpcap to find the optimal exposure time with the highest dynamic range.

The image was stacked with DSS using kappa-sigma funtcion. I also tried Siril and the same came out.

Does anybody have any ideas whats with the banding? I used dithering on every 10 frames. Is that not enough? 45 frames was dithered. Perhaps the dithering was not strong enough? Or is this a camera specific problem?
Any advice and info would be appreciated.

CS
Haakon

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dkamen

Mar 12, 2022

Hi,

This is supposed to be corrected by flats. Check your master flat and you should see a similar banding. If you don't see it your flats are wrong.

If you see it, the fact that it isn't calibrated out means your flats aren't working. 99% of the time this means a problem with darks or dark flats. Perhaps a light leak? Or maybe you have to match gain and offset over all your subs.

Cheers,

D

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Haakon Rasmussen

Topic starter

Mar 12, 2022

Hallo,

thanks for your answer. I have rechecked all the different frames to what gain and offset they have. They are all the same (gain 0, Offset 12). On my flatframes i see the vertical banding, but not on the masterflat. What does that mean? Can I restack the calibration frames in another way? The Master darkflat and Master dark does not show any banding or streaks at all. I'll try to stack with ASTAP to see what happens.

CS
Haakon

Haakon Rasmussen

Topic starter

Mar 12, 2022

Hallo,

stacking with ASTAP didn't help. Here is the masterflat and masterdark. The masterflat seems to bright. It has to peaks with value 17200 to 35900 ADU.
They were made by ASTAP.

CS
Haakon

Claudio Tenreiro

Mar 12, 2022

Hi, I use the same camera with Gain 12 and Offset 30, and I had no problem but, having said that, I did struggle a bit with flats files. My problem was to get the proper spectra using SharpCap, at around 50%, after a while it was fine.

Rafał Szwejkowski

IOTD Staff

Mar 13, 2022

The banding is you not swamping the sensor noise at 0 gain. Either expose longer or use higher gain. Sharpcap analysis fails in this regard.

Haakon Rasmussen

Topic starter

Mar 13, 2022

OK. I'll try to up the gain a bit. But if you look at my masterdark you see exact the banding that should be removed from the masterlight. I wonder why it is not working…

Rafał Szwejkowski

IOTD Staff

Mar 13, 2022

It's not removed by the dark, it's not structural per se but it creates structures after stacking. I have 6h of material made at dark sky new moon that showed the same thing and it's not recoverable.

Andrea Alessandrelli

Mar 13, 2022

I had a similar issue at 0 gain with the ASI1600MM-Cool and 30 sec exposures. Raising the exposure time above the minute solved it.

Rafał Szwejkowski

IOTD Staff

Mar 13, 2022

Yes, it's basically being underexposed, I got caught by it in the dark sky environment where 0 gain 60s RGB exposures just didn't swamp the sensor.

Haakon Rasmussen

Topic starter

Mar 13, 2022

Hallo trans-at and Andrea,

you're both right! Will it help if I just increase the offset, or is it more important to increase the exposure time? At first I set the offset to 76 and had a Histogram from 4700-65000 with exposure time from 60-240 S. Can I increase the offset, thus swamping the sensor? Or it is better to leave the offset at 12 and instead use higher exposure time?

CS
Haakon

Rafał Szwejkowski

IOTD Staff

Mar 14, 2022

I'd leave the offset and either increase gain or exposure time. My choice would be to shoot with unity gain (120 for ZWO version) which is the low-noise conversion mode. It's the safest choice.

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Haakon Rasmussen

Topic starter

Mar 14, 2022

I will!
Thanks!

Andrea Alessandrelli

Mar 14, 2022 · Edited: Mar 14, 2022

The 0 gain setting has indeed the highest read noise, but I personally like it. Under the light polluted sky where I live (bortle 6/7), it allows me to do longer exposures, saves a lot of space in my HDD, processing time and it doesn't make me feel like I'm doing lucky imaging. I also think is a setting that pays off with images with a lot of integration time.

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Haakon Rasmussen

Topic starter

Mar 14, 2022

Hallo Andrea,
Thank you for your help!
I totally agree. Gain 0 has also the highest dynamic range and full well. The noise is normally not a problem if there are a lot of light frames to stack.

CS
Haakon