Quote:
Originally Posted by Peter Ward
Peter,
As a zero second exposure is not possible with SBIG cameras, I am puzzled as to why anyone would want to use them, as they are already contained in the dark frame data.
A bias frame is simply a zero second dark, hence if you take any dark frame it consists of: a zero-second dark + x-second dark.
Also the dark map in SBIG cameras, from what I understand, while superbly consistent, is not truly linear.
Hence best practice to to use a library of darks taken at temperature x, and exposure time T, that obviously need to match your lights.
I've found much more value in simply getting excellent quality flats (I prefer sky flats....in fact they were the only flats that consistently worked with a back-illuminated chip I was running some years back )
Playing with Bias frames can often induce a bunch of artefacts that simply aren't in the data. I personally never use them.
Cheers
Peter
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Understood Peter. I took the opportunity of lousy weather up at Coona yesterday to take a huge number of flats with an EL panel - 80 - 100 of each. The download pipe has been running hot. I've also taken plenty more darks.
Unfortunately, I have yet to find a way to calibrate files in PI without using a bias frame. Without it, the flats overcorrect. Time for some more research.
Quote:
Originally Posted by Shiraz
Pete
Peter may have identified the problem. I understand that Pixinsight automatically compensates for variations in chip temperature and exposure time by scaling the master dark, so bias subtraction is essential. If the SBIG cameras cannot provide bias data or if they have non-linear temperature/time profiles, the Pixinsight calibration scaling algorithm will not work properly. Not sure what you can do about it though, short of using some other software to calibrate your data, using a set of darks that exactly match the times and temperature of your light subs, as Peter suggests.
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Ray, you are right. There may be a way to do this in PI but I have yet to find it. I am trying to use PI for all processing and have overcome the UI hurdle. Now its down to getting it to play nicely.