Re: Linear range of the chip?

[Tom Droege <tdroege2@earthlink.net>]

Arne has a nice scheme involving several bias frames and several flat 
frames which gives you the gain and noise level of the cameras.  He might 
repeat it here so that I do not garble it in presentation.  I get gains of 
2.5 electrons per ADU.  Noise level I have (purposefully) forgotten.  It is 
much less than my sky noise.  Some of the rest of you will want to check 
this.

The way the cameras are set up, the pedestal is at around -25,000 
counts.  This puts 80,000 e- at +7000 so there is plenty of room around the 
linear range as encoded by the ADC.  The non-MPP full well is 200,000 or so 
e- so the adc does not completely cover this.  Thus you can get saturated 
signals out of the ADC.  Full scale on the ADC is very far beyond the 
linear MPP range.

I really recommend that every one runs something similar to Arne's gain and 
noise check algorithm on each camera.

Tom Droege

At 11:44 AM 6/8/03 -0700, Arne Henden wrote:
>There are good descriptions of determining linearity in the
>Berry/Burnell AIP book.  While the CCD may be linear to its
>saturation point, you do not not necessarily know where that
>point is (Tom put it close to the ADC limit).  Likewise, at
>the short end, you run into shutter problems and it is useful
>to know at what minimum exposure everything works correctly.
>Along with the linearity, learning about the gain and readnoise
>are important parameters.  Not all CCDs are created equal.
>Not all PC boards get assembled the same.  Tom does real good
>at this, but a double-check is always good to perform.
>   The more you know about the CCD/camera you are using, the
>better you can make your observations.
>Arne
>
>Tom Droege wrote:
>>Rob,
>>I did this a while back with my flat field box.  I think I wrote it up 
>>for the list, but I can't find it.  I did not make it a TN.  Sigh!
>>Should have.
>