Taking photos of displays... - test-drb@ccmp.vtda.org

2 Mar 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