Dark frame is completely dark on SV605cc

[Ehud]

Hi Robin,
Maybe its li8nked to the previous issue I reported' but I am not sure.
I created Dark frame for the SV605cc, and it's completely black. Se attached log.
I also created Dark frame for my ZWO ASI678mc, there it's fine.
Thanks,
Ehud.

[oopfan]

Just a guess but you have Black Level set to zero. (I say a 'guess' because I am assuming that Black Level is the same thing as Offset for your camera. Different manufacturers can't agree on a common name.)

Brian

[Ehud]

Thanks Brian.
It is 0, but trying to increase it just made the Darks less black, but still uniformed

[admin]

Hi,

I would suggest opening the camera with the <CTRL> key pressed to stop it from reloading previously saved settings - I can see from your capture settings file that you had some odd things enabled including somewhat strange display stretch settings that mean anything below 50% image brightness would appear as completely black on screen.

Hopefully with the controls reset things will behave as expected. If not, let me know as I have a 605CC that I can test with.

thanks,

Robin

[Ehud]

Thanks Robin.
I closed the camera and reselected it with the <CTRL> pressed, and took te dark frame again. No change, still completely black.
Maybe a hint - Last night I also tried Substract Darks - Hot and Cold pixel removal, and it did nothing as much as i could see.

[Ehud]

Hi Robin,
I can't get it working well.
Please test with your camera.

[Ehud]

Hi Robin,
I did a carful test - and there are two dark pixels - please zoom to 100% or more and you'll see it on the right & left edges of the pictures, a bit above the middle.
Still, this is much less then he 'real' hot-cols pixels I see when doing stacking.
Please also check with your camera.

[Ehud]

... and I did another test - increasing gain to max: 600. Please see attached. Here there are few more pixels, but much less then what I would expect. Might it be that Gain value has some error when taking darks?

[admin]

Hi,

I have to say that looks pretty much fine to me - I downloaded the image and loaded it into SharpCap's test camera then stretched it and I can see that there is definitely a random background in the image

Screenshot 2024-04-17 194333.jpg (394.79 KiB) Viewed 1091 times

If you view the histogram in SharpCap while capturing dark frames you will see that the image is not perfectly black.

I would note that the image is very close to black when the 'black level' is zero with these cameras, and that should be avoided. To adjust the black level, capture short exposure dark frames (<1s) while viewing the histogram and adjusting the black level. Ensure there is clear space visible between the left hand side of the graph and the histogram peak. With my 605CC, I find a black level of 7 is reasonable at minimum gain, at gain 300, a value of about 40 is required and beyond gain 400 you cannot adjust the black level far enough to get good separation (this latter does not matter as you are unlikely to take deep sky images at gain 400+ except for throwaway images for focus/plate solve/etc).

cheers,

Robin

[Ehud]

Thanks Robin.
I followed your advice -
1 - Captures Dark of 10x500msec with Black level set to 40
2 - Used this Dark when Stacking using 5 sec. exposures.
3 - The dark trails & pixels gone

I have few questions:
1 - Have I done right by using same Black level for Darks and Stacking?
2 - Have I done right when using Darks made through 500msec exposures' for Stacking 5sec. exposures?
3 - And last but not least - I am having difficult time to understand why Black level should be higher, in my logic it's like pixels below it will be considered black, and by putting it to a high number I also reduced the dynamic range. Please help me understand.

Ehud.