No bias calibrated flat - almost complete banding elimination

[pfile]

of course, i wonder if the longer the exposure the more the banding seems to be, since the histogram really needs to be agressively stretched in order to actually see the illumination profile.

if i look at one of these things in the canon DPP tool, they show no vignetting.

i guess i'll calibrate my lights with and without the master flat and see what i get.

[georg.viehoever]

The EL panel that I have flickers at a frequency invisible to the eye (>25/sec). So if I am using short exposure times (I dont rememember what actually is "short"), I see bands on my flats. So what I did was to make the EL panel dim by attaching 2 layers of paper on top of it, and then taking the flats with exposure times >2 seconds.

May be thats part of your problem. Try what you get when you expose the EL panel at 1/100 secs or so. You may see severe bands if yours works similar to mine.

Georg

[pfile]

that's interesting... previously i was using a fluorescent bulb in a lightbox (for proofing slides) and it has a 60hz flicker. i always tried to make my flats at least 1/6s in this case.

i thought the EL panel was in the 10s of khz range as far as any flicker. the power supply makes a high-pitched whine.

i'm not sure how i can make the exposures any longer... i'm using iso100 and overexposing as far as the camera's metering is concerned.

anyway, i have banding in the calibrated stack with no flats, and i don't think it's much worse when i use the master flat. as usual the blue channel is the worst and i think this is due to the CLS filter.

[astropixel]

To what extent do laptop screens contribute to banding. If I debayer and ABE my flats they look good. They won't work in IC like that, but they look OK. The problems arise when calibrating the lights. Same channels affected using a CLS-CCD filter.

Question. Is it necessary to take flats at the same f/ratio as the subs if longer exposures are perhaps, better. Would it be even better to take flats at the same iso as the lights?

[pfile]

unfortunately, i think you have to use the same f/ ratio, or the spots and vignetting will be different.

[astropixel]

of course vignetting and spots