Taking photos of displays...

Dwight K. Elvey dwight.elvey at amd.com
Wed Mar 2 14:18:37 CST 2005


>From: "Tom Jennings" <tomj at wps.com>
>
>>> From: "Tom Jennings" <tomj at wps.com>
>>>
>>> Unlike film, you can'y simply open the shutter and integrate the
>>> image over time arbitrarily. CCDs are extremely noisy; silver
>>> nitrate (etc) it's at atomic scale.
>
>On Wed, 2 Mar 2005, Dwight K. Elvey wrote:
>
>> Actually, once compensated, CCD's have much more
>> dynamic range than film. They can be used to integrate
>> over long periods of time ( usually cooled ). They
>> have issues but don't confuse poorly compensated
>> camera's with the ability of a CCD.
>
>I realized astronomical cameras for example use CCDs, most
>definitely cooled, for very long integrations, but the context of
>the conversation implied hand-held, non-cooled, ordinary, cameras.
>I wasn't slagging CCDs or holding chemical film on high (though
>would that be out of character for this list? :-); just wanted to
>point out things aren't simply linear like that.

Hi
 It really depends on the actual CCD. I have one that
I use un-cooled but it is a low noise CCD. I have
used it for 5 min exposures. There is a static drift
that is different on each pixel. I compensate by
subracting the dark current field. This is not noise
but would look like noise when used in an uncompensated
photo. If one can make a dark field time exposure of
the same length of time, one can subtract that and
get a much better image, without cooling.
Dwight





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