[Aavso-photometry] Question concerning linearity of CCD chip

[Brian D. Warner]

Arne's interpretation is correct and it's admitted this is a crude test (exact words 
are "simple test"), meant mainly to find the ADU/CCD roll-over.

The reader is referred to the Berry and Burnell book for their more exacting method. 
Tom Krajci recently posted a reply with links to his site, where he has an excellent 
description for thorough analysis.

I make it very clear in my book that it is a starting point in many places and that 
other resources, Henden/Kaitchuck, Berry/Burnell, Howell, and others should be 
consulted for more detailed information.

I've answered Larry off-line as well.


Clear Skies,
Brian D. Warner
Palmer Divide Observatory/Space Science Institute
http://www.MinorPlanetObserver.com

Collaborative Asteroid Lightcurve Link (CALL)
http://www.MinorPlanetObserver.com/astlc/default.htm


----- Original Message ----- 
From: "arne" <arne at aavso.org>
To: <actuary at mchsi.com>
Cc: <Aavso-photometry at mira.aavso.org>
Sent: Wednesday, September 26, 2007 11:05
Subject: Re: [Aavso-photometry] Question concerning linearity of CCD chip


> actuary at mchsi.com wrote:
>> To All:
>>
>> I am reading "Lightcurve Photometry and Analysis" by Brian D. Warner.  On page
>> 91, a procedure for testing the response linearity of a CCD chip is
>> described.  I am confused as to the meaning of the sentence "Find the average
>> of the maximum ADU values for each star at a given exposure...".  Say 5
>> imagess at 1, 2, 4, 8, and 16 second exposuress are taken. For a specific star
>> there are 5 images at 1 a second exposure.  Takling the maximum ADU for the 5
>> images for the specific star provides a singlr value.  However, the procedure
>> says to find the average of the maximum ADU values ... The average of the
>> single value is the same value. Since the test involves plotting the values
>> obtained through the application of the "averaging.. maxumum" algorithm by
>> exposure time, one does not average over exposure time nor over all stars.
>> Clearly I am misinterpreting the description of the procedure.
>>
>> I would appreciate some guidance as to the correct interpretation of the
>> procedure.
>>
> This must be from the second edition, as the page numbers and text
> do not agree with my original copy.  I'll try to interpret the statements
> above, with the understanding that they are taken out of context and
> I'd need the correct edition to fully consider the problem, and I
> certainly won't approve any linarity method without seeing its entire
> description.
>
> I think what is meant is that each star profile has a range of pixel
> intensities - highest in the center and then falling off like a Gaussian.
> For the 5 frames with the same exposure, you would pick the maximum
> pixel value found for a given star - that gives you 5 "maxima".  Then
> average those.  This is basically what Wolfgang suggested.  If true,
> this is a very crude method of determining linearity, sufficient to
> look for large deviations (such as saturation or ABG turnover) but
> not much more.
>
> Arne
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