Webcam Lens Question

[Marvin Rosen]

What is the focal length of a standard
webcam lens? Can one use a "C" mount
tv lens in place of a standard webcam lens?

[Benoit Morrissette]

On Fri, 04 Jul 2003 21:50:11 GMT, "Marvin Rosen" <puns@att.net> wrote:
What is the focal length of a standardwebcam lens? Can one use a "C" mounttv lens in place of a standard webcam lens?

The "normal" focal length of any camera can be found by mesuring the diagonal of
the sensor (or film). For exemple, using a 35mm camera, we find that the
diagonal of the film is about 46mm. Most 35mm cameras are sold with a 50mm
lens, wich gives a 52° field of view, about the same as the human eye.

Now, there is no "standard" WebCam lens because the various sensor arrays have
differents width! A 320x200 pixels array is smaller than a 640x480 one so the
manufacturer will ask for a "shorter" lens. I have a Logitech QuickCam Pro 3000
and the diagonal of the CCD sensor is about 10mm but the lens is slightly "wide
angle" so i believe that the "standard" focal length of many Webcams is about 7
to 8mm.

I have tried to use an old "Super 8" camera lens for my webcam but the "image
field" is not wide enough; i got dark and unsharp corners!! I think that a
16mm camera lens will be OK but then we will have a telephoto lens because the
standard focal length is longer.

Can we use a "C" mount TV lens on a WebCam? Yes, definitively, absolutly
positive!!! the "image field" is more than wide enough! BUT the focal length
is also too long, so you will get a tele-photo lens with a small field of view.

For the past two years i have been looking for a (cheap) replacement lens for my
webcams and my best choice is still 8mm or 16mm camera lens in terms of focal
length, field of view and image width.

P.S. Sorry for a few mistakes... i garantee you that my french is better than
my english!

Benoît Morrissette, Québec, Canada