Problem with Flats

So now I'm confused.com

All the "Light" frames I took had their appropriate dark subtracted, obviously the matching exposure dark contains the BIAS as well, so technically the BIAS was removed from the flats, my camera has a "BIAS" exposure where the exposure length is 0.00.

I plan on re-doing my flats, I reached out to green-witch the other day regarding the "Overscan" region and Lee has asked the question from Atik, he dis say that due to UK Astrofest it might be a while before he gets a response from them.

With regards to how well my darks are, the camera's shutter doesn't appear to let any light in, I've done some tests on that by pointing light down the scope and doing a dark frame, and then doing the same dark but this time without any light and there was no evidence of light leakage.

Regards
Simon

I've now completed this from 2 Sec all the way up to 148 Sec

Have not done the DTC Curve yet though

I have now done two DTCs

One based on Math STDEV, the other based on Average STDEV, whilst the Average STDEV one looks a lot cleaner, the Math one is all over the place

mjc wrote: I'm not sure why the value in col N is being subtracted - or even what it is.

Mark/Simon - this was a column that came from Richard Crisp. I didn't go into any major research about what precisely it was but if you alter the number, it changes the data points on the chart. If you look back at the original spreadsheet (log-log) and change the number in the first row (it will proliferate to the other cells) you'll see the points change. If you do it carefully, you can get the point to extend back to the y-axis.

Simon - I'm really not sure what to do with the BIAS at all... But you're correct - if a dark frame is used for calibration and it the same duration as a light (and same temperature) there is no need to also subtract a bias frame from the light because the bias is included. As you point out, even with my own images, the bias has already been accounted for.

All I can think of is that Bias and Overscan are not identical. If that is so, I'm even less sure as to how they are different.

You charts certainly indicate a nice linear response - to what, I'm not sure

Cheers
Dave

p.s any luck in Greewitch coming back to you?

dmcdona wrote: All I can think of is that Bias and Overscan are not identical. If that is so, I'm even less sure as to how they are different.

Bias will reveal any 2D patterns that just using the overscan will miss. I suppose you could construct a master overscan-bias frame and compare that to a master bias and see if there was any 2D pattern to worry about.

Here's what the Handbook of CCD Astronomy has to say about overscan -v- bias if it's any help:
farm4.staticflickr.com/3792/12443896865_6411841205_k.jpg
farm4.staticflickr.com/3799/12444396934_803b8098a5_k.jpg

Apologies for not keeping up with this thread. The simpler methods I used seem to give me acceptable results for gain, readout noise and linearity range. So out of interest have you seem much of a difference using your more involved methods? Once I get a bit more time I might be on to you to get a copy of these spreadheets and more advice

Thanks,
Al

So BIAS can do the same thing that Overscan can, but with the addition of 2D pattern masking, so if I look at this correctly I should not have to do any "Offset" if the 250+ Stacked BIAS frame is subtracted from my Lights (Flats), that's how I read it.....but I could be wrong