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Originally Posted by jase
Pete,
Where did you get a target ADU of 20,000 from? The full well depth of the SBIG 8300 is only 25,500! This may explain the over correction of the light frame data as I previously noted.
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Jase
I think there is a difference in nomenclature here. The full well capacity of the ST 8300 chip is about 25,500 e- which I understand converts to about 65,000 ADU. The Sky Flat Assistant sets by reference to ADU and I had thought that Maxim's graph function did the same. Feel free to correct me if I'm wrong on this.
Last night I tested flats with target ADU counts from 8,000 (co-incidentally) up to 30,000. It was late when I twigged to the error factor and dropped from 10% down to 2% and then 1%. Flats at 8,000 ADU yielded a very nasty vertical dark stripe down the image. The sweet spot (though still not that sweet) was at around 19,000 to 20,000 with a 1% error setting.
Its still not perfect - I am using 5 minute subs. I suspect that the uneven light will be less an issue at shorter subs. If so, applying the same flats will be worse rather than better I guess. Thats logical so its probably wrong.
Quote:
Originally Posted by jase
When you combine a series of flat subs, data rejection with clip the highs and lows (extremes) and level the data (assuming you don't use sum!!). Average or median combines will work well, if you want to get fancy, CCDStack's clip min/max or poison sigma reject are great.
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This bit is more of a challenge for me. I've set Calibration Wizard to the correct file and its identified in Set Calibration the relevant dark, bias and flat files. I've then created a master flat from the flats in that folder using median combine. The settings are as per your earlier post (albeit under a tab marked Advanced). I then open the light and calibrate it from the Process tab. I'm not sure how to level the data as you suggest. Is this an alternative to median combine?
Quote:
Originally Posted by jase
No, target ADU remains the same, its just that the exposure time to reach it will be shorter.
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Understood - thanks
Pete