[Aavso-photometry] Flat Stuff

[Arne Henden]

Richard Miles wrote:
> Arne Henden wrote:
> 
>> If I were you, I would test this.  I have yet to see an electronic
>> shutter that was perfect.  Our uniblitz shutters, for example, start
>> to leave an objectionable vignetting pattern for any exposure shorter
>> than 3 sec.  Flats are the most important calibration you will do,
>> and any error in the flats impact all science frames.  Test them in
>> many ways.
> 
> 
> Arne - thanks for making the point about shutter vignetting, it's a key 
> limitation with flats depending on the CCD camera.  The fast readout of 
> USB 2.0 interface cameras does help to increase the rate at which images 
> can be taken and saved to disk.  I use the SXV-H9 camera and image 
> readout/save times are between 1-4 sec depending on binning.  My 
> finished flats usually comprise an average of 100 frames.
> 
The interline chips are the exception to my statements about shutters.
Since the interline "shuttering" is done by quickly moving charge from
the imaging columns into adjacent light-blocked storage columns,
the differential exposure across the field remains constant, no matter what
exposure time is chosen; the only possible error is in determining the
actual exposure time used.
   My statements were more towards mechanical shutters controlled
electronically.  Sorry if I caused some confusion!
Arne