Flats working on some images, but not others... (no optical changes besides single digit focuser steps from thermals)

[pipnina]

I've had the scope set up all week, and took some flats a few times. But none of these flats seem to be working and over-compensate on some of my images. But on others, they're working perfectly... I thought it might be to do with focuser slop moving from one side of the mount to the other after a meridian flip. But I took one of the sets of flats on that suspect pier side and it still didn't care for it.

I'll admit to not using darks, but I made 150 bias frames and added those to the pixinsight calibration script and it still over-corrected the troublesome images.

I don't see how some of these images will over-correct, when the telescope is optically untouched one night to the next. Unless the thermal expansion and contraction night to night is doing something, but my collimation had held nicely...

And to be honest, when I went out and took fresh flats, they didn't even work on that same night's images, but my methodology hasn't changed (focuser in same position, or very close to it, as where the imaging will be done, artists illuminated A3 drawing pad in front of telescope, flat to the aperture, while I take flats that peak at close to 50% ADU).

I'll link some of these images and flats here.Flat_002.fits Flat_001.fitsmasterFlat_BIN-1_6224x4168_FILTER-O3_Mono.xisfmasterFlat_BIN-1_6224x4168_FILTER-O3_Mono.xisf

Light_2022-08-09T23-46-11_001.fits <- This light file corrects fine for me, from "night 2 redo" (So i think night 3)

Veil_Light_2022-08-09T01-32-48_006.fits <- This one corrects fine for me too, and it seems to be on the other side of the pier which might make my meridian flip theory a bit weak.

Light_2022-08-10T02-37-34_001.fits <- This one also seems to correct fine...

But then!NGC_6847_Light_2022-08-11T00-25-25_001.fits After no changes to the system all week. Suddenly the flats start over-correcting here! This is even the night I re-took them in the early hours of the morning, and those new flats still didn't work. I can't think of anything that's changed, and even if it had changed, why might my new flats *also* not work?

This is a source of constant pain. Makes me wish we could perform "manual" flat calibration through some assisted manner. The automated calibration systems just don't seem to work very well.. At least in my experience...

Flats are the most important kind of calibration, especially now that I have a camera with minimal noise profile (IMX 571) and no amp glow. But there always seems to be something getting in the way of them working right... They work some times, and not others. But I'm doing the same thing every time!

 

I realise now the two master flats have the same name, but they are made from different sub flats.

 

Anyone know what could be setting it off in this situation? I'm going mad here. There is a setting in my RisingCam that is on every time it power cycles (Auto Exposure) but I can't tell what it does and there's no documentation. I *try* to keep it turned off if I remember.

[Fegato]

I've had problems in the past with flat frames over-correcting and so on. I have used an A3 panel like yours, although I now have an Aurora panel to fit my 11inch RASA. I don't know what's going on with yours I'm afraid. But the thing that has improved my flats the most was getting a very solid aluminium dew shield with good flocking - I put the flat panel on top of the dew shield with the scope pointing up. I suspect I may have had some impact previously from a more wobbly and wonky dew shield.  Depending how yours are taken, maybe you are getting impact from extraneous light sources?