Problem with Flats

That was for the whole image and not an ROI, I can re-do this using a POI using the same flats and darks correct?

Combined STDEV is where Flat 1 has 5000 added to is, then Flat 2 is subtracted using ImageJ and the resulting STDEV is generated

Yes - you don't need to reshoot any images.

Choosing the Region of Interest (ROI) is important. You want an area that's sufficiently large to be somewhat representative but you want it to be as clear as possible of any dodgy pixels (hot or cold).

I shot a 4 hour dark (probably OTT) to choose the ROI. As an aside, the reason for shooting darks at ambient temperature is so that the pixels gather their charge quicker - if you cool the CCD it'll take a longer dark exposure. Temperature control though is helpful - hence me choosing 15 degrees C - just below ambient but controlled by the electronics to stay at that temperature.

I chose an arbitrary region of 140 x 140 pixels (initially I chose 100 x 100 but managed to find a clear larger area later on). As long as it isn't too small (e.g. 5 x 5), choose what seems appropriate.

The combined STDEV seems to be the pixel-math part of the process. But you'll need to do it again.

Here's what (I think) you need to do:

1. So, shoot a long-ish dark (maybe an hour or two) so you can choose your ROI.
2. Note the co-ordinates of the ROI and length/width.
3. With each of your darks
3a. Crop the image to the ROI
3b. Record the data for each cropped image at each exposure duration and put into a/the spreadsheet
4. With each of your flats/lights
4a. Calibrate each image with the appropriate flat-dark
4b. If your flat-dark is the same duration as the flat, do not subtract the bias - its already in the flat-dark
4c. Crop the image to the ROI
4d. Record the data for each cropped image at each exposure duration and put into a/the spreadsheet
5. Go back through all the darks and flats and do he pixel math (your Combined STDEV calculation) and populate the spreadsheet with the data.

That'll keep you busy...

Dave

So I should load up my 3600 Dark frame and stretch it a little to find the quietest 140x140 area, note down the coordinates and use those coordinates for all the flats and darks?

Yes.

But you can choose an ROI of any reasonable size you want. I used 140 x 140 pixels - you might choose something different. Then yes, use exactly that ROI (co-ordinates and size) on all images as described below (calibrate that those require calibration BEFORE cropping to the ROI).

Done that

Some bizzare results though, emailed you the values

Simon - the results at 84+ seconds are showing that the CCD is maxed out (i.e. full-well). So that's normal.

I'd recommend adding more lights (flats) for 79, 81 and 83 seconds (three more images x 2).

Can you put all the data in the spreadsheet? Seeing columns of data in the email is not very helpful... Put the data you have into the columns you *think* they should be in. We can take it from there...

Thanks
Dave