"Ed Anson" <EdAnson@comcast.net> wrote in message news:3F162902.2010101@comcast.net...

[...]

> OTOH: If the two optical systems gather the same amount of light and are

> arranged so that each projects the same image onto the corresponding

> sensor, then I agree that AOFBE each pixel will receive the same number

> of photons on each sensor. But to do this would require that the lenses

> have very different f numbers (speeds), with resulting effects on depth

> of focus, cost, etc.

In all of this, the lens, etc. can be removed as irrelevant (and was, by the

phrase, "all else being equal"). Since this is a discussion of CCD size

alone vs. sensitivity, only the CCD area need be a concern. RGB's

checkerboard in the rain covers the issue well enough, but perhaps easier

to see is a comparison of two photo-electric cell arrays out on the same

day (and therefore exposed to the same light intensity, assuming similar

orientation, etc.). One is 2"x2", the other is 20'x20'. All the cells in each

array are connected in parallel and therefore produce the same voltage.

Which produces the higher current? (Or, all the cells in each array are

connected in series. Which produces the higher voltage?) In these

discussions, it helps to strip out the irrelevant parts (the equal parts

of the equation that drop out...;-), then reduce what remains to a

familiar and similar situation...

> My point is: Physics and economics dictate that changing the size of the

> sensor requires other things to change as well. That can make it a bit

> tricky to predict the performance of a practical system. And none of

> this takes into account the effects of sensor size on the intrinsic

> noise of the device and the circuit used to read it.

Yes. But the question was a simple one of sensitivity vs. size of the CCD,

all else being equal. There are MANY other issues involved in a more

complete discussion of the question of video imaging, but these are irrelevant

(but interesting...;-).

> [BTW: I think the biggest advantage of the larger sensor is that it

> allows use of longer focal length lenses, with resulting ease of

> controlling depth of focus.]

There is more, of course: the noise issue that you mention, sensitivity,

tonality, etc.

--

David Ruether

d_ruether@hotmail.com

http://www.David-Ruether-Photography.com

Hey, take a gander at www.visitithaca.com, too...!