Annoying dark bands in astrophotos from Canon M50

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hhzhang
Posts: 730
Joined: Sun May 10, 2020 4:11 pm
Favourite scope: 115mm APO

Annoying dark bands in astrophotos from Canon M50

Post by hhzhang »

I noticed something like a narrow darken bar overlay in my stacked photos.

At home I took dark frames, dark flat frames, flat frames and bias frames. After applying these frames to stacking, the dark bar overlay just did not go away.

I then set to investigate it to understand what went wrong.

In my early collection of master dark frames, the ISO400-30s one shows the most prominent problem. And the dark bar only appears in the "R" channel.

Note that I am not debayering the raw data, simply splitting the RGGB into separate images. And all the images are equalized in GIMP.

Image

I did more tests. Unfortunately the results are inconsistent: under the same ISO, the pattern varied significantly.

Image

Lastly, I tried to see if temperature plays a role here. Many many frames later and after stacking subgroups of frames, I arrived at this picture -- all the master frames (as sub-pictures here) are equalized together so that pixel values can be compared directly.

Image

Evidently, temperature is indeed a key factor here. The bad dark band in R channel becomes visible after the temperature exceeds 35c-36c.

Now the question turns out to be: how to control the camera temperature in the warm and humid local weather?
rifleman175
Posts: 81
Joined: Wed Aug 22, 2018 5:16 pm
Favourite scope: Skywatcher Esprit 100ED

Re: Annoying dark bands in astrophotos from Canon M50

Post by rifleman175 »

As far as I know, there is no way to control sensor temperature for DSLRs, the only way is to upgrade to a cooled CMOS/CCD camera if you are serious about astrophotography. The most popular brands are ZWO and QHY.
hhzhang
Posts: 730
Joined: Sun May 10, 2020 4:11 pm
Favourite scope: 115mm APO

Re: Annoying dark bands in astrophotos from Canon M50

Post by hhzhang »

rifleman175 wrote: Sat Aug 15, 2020 2:07 pm As far as I know, there is no way to control sensor temperature for DSLRs, the only way is to upgrade to a cooled CMOS/CCD camera if you are serious about astrophotography. The most popular brands are ZWO and QHY.
Well I have already got a small astro cam (ASI183MM Pro). But it is always fun to explore the full potentials of DSLR/mirrorless - - especially being encouraged by other fellow astrophotographers here doing that.
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