[Aavso-photometry] Question concerning linearity of CCD chip

[actuary at mchsi.com]

Brian & Arne:

Thanks.  I really appreciate the efforts by both of you and others to help me 
understand the material.

Larry


----------------------  Original Message:  ---------------------
From:    "Brian D. Warner" <brian at MinorPlanetObserver.com>
To:      "arne" <arne at aavso.org>, <actuary at mchsi.com>
Cc:      <Aavso-photometry at mira.aavso.org>
Subject: [Aavso-photometry] Question concerning linearity of CCD  chip
Date:    Wed, 26 Sep 2007 17:44:55 +0000

> 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
> > _______________________________________________
> >
> > Aavso-photometry mailing list
> > Aavso-photometry at mira.aavso.org
> > http://www.aavso.org/mailman/listinfo/aavso-photometry
> >
> > 
> 
>