[Garbz (Chris)]

Well I'm officially bashing my head against the wall. After many years of no issues I can't for the life of me make flats work. I just don't get it. For some reason I am now unable to put a photo together.

My flats are overcorrecting. The vignetting has gone the opposite way and the dark dust spots have turned to light dust spots and I'm at whits end as to what on earth is going on at this point.

In the attachment you can see the examples of my problem. On the left is an overcorrected stack where the flats were generated by pointing at the sky with a white t-shirt. In the centre was the original stack. This is pretty much normal that it looks so green. On the right was another attempt at stacking tonight again made with a tshirt but this time lit by the fluros in the house. The fluros make a very orange flat that results in a huge blue tint to the final image.

In the second picture are the photos with an unlinked screen transfer function.

In the third photo is a shot of one of the flats and some statistics of what I'm doing.

/Edit: I should also mention that relying on DBE along is not an option. My sensor is filthy and the dust spots will require the flat frames to correct.

So I was targeting the lower 1/3rd of the histogram and the flats average at around 15000 ADU. This low value was a second attempt as the first attempt which generated the left picture I thought I may have had had problems with non-linearity. But I can't resolve that right now.

The flats had bias and darks set so I loaded everything into the dark frame selector including a set of 300second darks for the light frames and a set of 30second darks for the flat frames.

I'm at wits-end. I have no idea what I'm doing wrong anymore. Has anyone got a clue?

Solution

My lights and flat frames were taken with a different gain and offset value from my darks and bias master frames which I had in my library. I blame a software update which may have reset the settings in EZCAP.

Anyway the wrong gain settings in the bias frames introduced a scaling issue when calibrating the flat frames. Flat + Lights themselves worked just fine. It was only when Bias frames were added that they failed to correct properly.

Thanks all for your help.