Help with Flats & Darks (294MC)

[bertinspace]

Just setting up my new (used) 294MC camera...

I noticed my flats (that auto exposed at 300ms) at gain 121 have a large round white glow in the centre of the stretched preview. This same glow appears in shots of deep sky as well.

The 120second darks also have a strage artifact in the centre of the image.....

is the sensor damaged?

[AstroViking]

Hi Arnold,

You'll need to use longer exposures for your flats. The '294 and '183 series of cameras from ZWO/ASI are well known for not giving good images if the exposure time is under 3 seconds.

For my '183MC-Pro, I use 5 second exposures for the flats and dark-flats.

I can't help with the UFO-like glow in the centre of the frame - that's odd and nothing I've seen before.

Cheers,
V.

[Nikolas]

That is a frosted sensor it is either the desiccant that needs to be changed/recharged or you need to cool slower in stages.

[bertinspace]

After some experimenting.....the vignetting is normal and just exagerated by the auto stretch in ASIair. After stacking and adding to final stack the flats worked perfectly

Results attached:) https://www.dropbox.com/scl/fi/rirmg4xumvurfbzrzqeab/NGC3576.png?rlkey=fno3thspl570pvvpx xpnhkdzh&st=kjhlh73m&dl=0

[ChrisV]

Look at the flats linear not stretched - the later exaggerates things. And it should already be visible unlike lights

[AlexN]

IMX294 sensors TYPICALLY do not like exposures under 3 seconds in the gain range of 120 to 150 - strange, I know, but it's a well documented issue...

My Player One Artemis-C is a IMX294, and I experienced similar issues around flat frames until I got a very dim light panel and was able to take 3s UV/IR flats, and about 7s narrowband flats...

As for your dark frames not calibrating out the sensors amp glow - I would make sure you're being very careful about your dark frames...

Your darks need to be at the same sensor temperature, same duration, same gain and offset as your light frames.

I've made a relatively extensive dark library for my camera, (as I have lots of cloudy nights to play with).
I have 30, 60, 120, 180, 300 and 600s dark frames, for all of the following scenarios.
-10°c sensor when the cooler is sub 50% loaded.
-10°c sensor when the cooler is over 50% loaded.
-20°c sensor when the cooler is sub 50% loaded.
-20°c sensor when the cooler is over 50% loaded.
At both Gain120, Offset 50 and Gain0, Offset 100

I have them all integrated into master darks, and I just select the master dark that most appropriately matches my light frames... If it was cold outside and I was running -10°c, and the cooler was at 24% usage, I use the low power dark... but if it was warm and I was running -20°c at it was at 74% cooler power, I run the high power -20 dark

Also, its 100% never a good idea to trust an auto-stacked, auto-calibrated result that's being auto-stretched then displayed on a phone/tablet display... Never judge your images on anything less that the machine you're going to process them on..

[Leo.G]

I've been using an A3 copying board (variable output LED lighting) for several years for doing my flats, mainly with a DSLR but I've never had a problem doing it in this manner. I mentioned to an astronomer friend in Arizona I've known for 20 odd years online and he bought one online and loves it. He has a better range of cameras and mentioned he's recommended it to other friends locally.
My unit was only a cheap Aldi unit and it's been great for the purpose and conveniently runs off a power bank and is light and easy enough to sit on an upturned telescope. Al long as I get my scope near vertical after/during my imaging session it sits there by itself and suitable for up to 10" scopes I believe depending on tube size.


I keep the original plastic clear sheeting on mine and peel it back when I want to use it and fold it back over to keep dust and marks off the board.

[AlexN]

I have tried one, and with every other camera sensor I've ever used (KAI-11002M, KAF-8300M, ICX-453 and ICX-413) it was fantastic.. With the IMX294, however, those dimmable panels alone can not get dark enough to achieve a 3 second flat with just a UV/IR filter. with a USB powered tracing panel, I needed to use 8 layers of 50% neutral density gel filters stacked on top of each other to bring the light intensity down..

This is, however, because I run my camera at a gain of 120.. If I run it at between 0 and 119 or 151 to max gain, I can shoot 0.02s flats without any weirdness at all. Its just when I shoot between 120 and 150 gain, the cameras sensor does some weird things.

As I mentioned earlier, the IMX294 sensor is a strange beast, and this is a well documented 'issue'

[Leo.G]

That is the camera I would like to obtain one day when finances permit (294mc). I'll keep this information in mind, thanks!
Now where did I put my drawing board...