|
Here's part two... I spent hours last night capturing images and 6 sets of corresponding flats at 1s, 2s, 3s, 4s and 6s (20 of each). I captured the flats in groups of 5 and rotated the light box 90 deg between each set just to make sure there is no chance of un-even illumination from the light box. I've now spent 6 hours processing all these and have discovered the same issue no matter which set of flats I use! It appears the flats are over-compensating for vignetting making a light pattern around the image when the flat is applied rather than a dark one with no flat.
I'm wondering if this has something to do with the QHY8 being OSC and how deep sky stacker handles this. According to the DSS help file it applies the flat for each channel separately and as long as the peaks for the channels are between 1/3 and 2/3 of the maximum on the histogram it shouldn't be a problem. I've ensured I used a qualifying set and still get the same result??
The first image below is the stack of lights without flats - the second is the same stack of lights with 20x4s flats applied.
|