Re: [APML] Dynamic Range of CCD

[Jerry Lodriguss <jml@astropix.com>]

Hi Dave,

Thanks to everyone who tried to answer my question.  I guess I foolishly 
thought it was a simple question, but I don't know if it is my fault or 
that of the people trying to answer it, but I don't feel like I have a clue 
as to what the answer might be, even after all of the attempts at answering 
it.

Let me explain what I consider dynamic range to be in terms of exposure 
latitude.  I consider it to be the difference between the maximum and 
minimum amount of light that the device can accurately record with detail 
at both ends of the range.

I guess it is more complicated for CCD, it sounds like maybe the dynamic 
range might be different for long and short exposures. That might be true 
for film too if one considers reciprocity failure for long exposures for film.

OK, then let me phrase it like this:

For film, for a normal daytime exposure, I can set up a gray card in the 
sunlight and photograph it at the correct meter reading for the speed of 
the film.  Then I can start bracketing the exposure, intentionally 
over-exposing it and under-exposing it.  At some point on each end, the 
film cannot differentiate detail anymore. For instance, on chrome film, it 
just becomes totally transparent with no tone.  Now, if I record my 
exposures when doing this test, I can tell you that at a certain given 
brightness for the gray card, say for an example off the top of my head, 
with ISO 64 speed film, the correct exposure for the gray card is 1/60th of 
a second at f/16 and the film will not record any tone in the gray card if 
I overexpose it by, say, three stops, or underexpose it by four stops.

This is my definition of exposure latitude and dynamic range. In this 
example, the film would have 7 stops of dynamic range.

I think this is a fairly standard concept and definition in the film world.

Now, what I want from you CCD guys is the answer for what is the dynamic 
range of a CCD based on this definition. It seems simple enough. <G>

Cant' this exact same test be performed with an ST-10E camera hooked up to 
a camera lens?

Jerry




At 04:08 PM 4/5/2002 -0500, you wrote:
>Hi Jerry,
>
> > Could one of my fine CCD brethren tell me what the exposure latitude, or
> >  dynamic range is of a typical astronomical CCD camera, preferably the
>ST-10E.
>
>Dynamic range in electronics (my business) is usually defined as the
>difference between the clipping level (or the 1dB or 3dB compresion point)
>and the noise floor.  Is this how you define the dynamic range of an image?
>Or do you like some other definition?  There are several possible definitions
>that convey different information about the detector.
>
>The CCD is noise limited at short exposures by readout noise and quantization
>noise.  At long exposures it is limited by sky background plus object shot
>noise, dark subtraction and flat fielding noise and inaccuracy.  The clipping
>level is, of course, the electron well depth, which depends on the detector
>and the amount of binning.
>
>If you can define dynamic range for us, then we can estimate it under certain
>conditions and for certain cameras.
>
>Dave Rowe
>
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