Flat Out of Ideas

[SeeMeade (Colin Meade)]

Help! Heavy color pattern coming through in individual flats with 294MC Pro camera and Optolong L-Extreme filter. I can see a lot chatter online about issues with patterns like this with this combo of the 294MC Pro camera and Optolong light pollution filters but none of the suggested solutions I can find are working for me. I have tried:

- Different flat capture software: SharpCap Pro, NINA, ASI
- Sky flats vs LED Panel
- Different diffuser membranes: t-shirt, paper, bedsheets
- Different exposures from 250ms-25s
- Different gain from 120 to 300+
- Cooling to -20C, 15C or no cooling
- Ticking the box for monochrome flat or not

Replacing the filter with an empty filter drawer solves the issue, but then it's not a "proper" flat and needs different exposure & focus settings?

Any suggestions? I bought the camera second hand on here, and don't have warranty...

[ronson]

Hi Colin,
From what you described this appears to be related to the filter rather than the camera. It's not clear what the problem is though. There is the color pattern indeed, but does this affect the calibration of your images?

[doppler (Rick)]

Hi Collin, check this YouTube tutorial out.


https://www.youtube.com/watch?v=nl_LQDmkg2o


Rick

[SeeMeade (Colin Meade)]

Thanks for the You Tube link. Some good tips in there and I'm already following some of them, but his flats are a mottled grey, rather than the color pattern I have with a very distinct red border and diagonal like mine. If I add this flat to the light sub, it adds this red border and diagonal to the picture.

Last night I tried rotating the filter 90 degrees, but not the camera, and the pattern was unchanged - it did not also rotate.

Any other ideas?

[Startrek (Martin)]

I found this post on the ZWO forum ( I’m a member )
Don’t know if it helps but probably worth a read

https://bbs.astronomy-imaging-camera...ro-flats-issue

Chen (w7ay ) is a very knowledgeable astrophotographer and has helped me out on a number of occasions with my 2600 camera

Historically the 294 has been a good but temperamental camera



Cheers
Martin

[Addos (Adam)]

As Martin pointed out the 294 colour and mono chips (had em both) are quite 'quirky' but in my experience work fine once you get your calibration for them right.

Thanks for confirming the flats do impact the calibrated image, thats important. if it doesnt hurt your final image no action required.

I'd suggest trying some of the below that I found worked for me:

* 294 flats must be calibrated with matched flat darks. are you doing that?
* subs less than around 2 seconds with these sensors produce inconsistent adu readings, flat and flat dark subs must > 2s. I found the only way I could do this with luminance frames at unity gain was to wrap 3 or 4 tshirts over the led panel, for example. this is also why you dont calibrate 294 images with Bias.
* strong anecdotal evidence that sensor temp on flats doesnt matter. flat dark temps need to be same though so you should still do with cooler somewhat running so this can be controlled.
* if you've been using this camera and a master dark library for a while (>12mths), update it. small degradation in sensor over time can also affect how the master dark calibrates. think adam block did a couple of vids on this explaining the how/why.
* its a colour sensor flat youre making. dont change settings to mono / disable debayering
* i have seen some anecdotes thrown around about the 294 ar / uvir coatings not playing nicely with some filters, but didnt experience this with either of mine. if you work through the above and still got a problem, maybe double check theres no light bleed anywhere in your imaging train?



hopefully some of that may help you. good luck!

[SeeMeade (Colin Meade)]

Just to close this out after Martin's and Adam's suggestions, I ended up trying another filter (Antila's ALP-T) and had the same result of patterned flats. It appears to be a common effect between the 294 sensor and light pollution filters.

However, I've since found out that this color pattern WAS actually appearing in the lights too, it simply only became visible though in a single sub if there was extra "light" in the sub e.g. passing cloud, approaching twilight or shooting towards the moon or in a brightly moonlit sky.

In short, it's calibrated out fine in the final image by using these odd flats.

Thanks all for the input.