"Neil Harrington" wrote in message
. ..



The 1/1.8 type is about 5.32 x 7.18 mm, and the 1/2.5 type is 4.29 x
5.76 mm.

You can find the *approximate* size of any sensor if you know the actual
focal length of the camera's lens and its 35mm equivalence, both best
taken at the long end of the zoom for the sake of better accuracy.
Dividing the latter by the former will give you the digicam's lens factor.
Dividing the diagonal of a full 35mm frame (about 43.2 mm) by the lens
factor should give you the diagonal of the digicam's sensor. However, this
is a rough method (because the camera lens's stated focal length may not
be precise) and may not give you exactly the figures above.

Expanding on this a little:

Most (but not all) compact digicams have sensors in the 4 : 3 aspect ratio.
This should be convenient for finding the diagonal of the sensor, since it's
the 3-4-5 right triangle familiar if you remember your geometry, i.e. if one
side is 3 units and the adjacent side is 4, the hypotenuse must be 5.

So in the case of the 2/3 type sensor used in my Coolpix 8800 for example,
the 6.6 x 8.8 mm sensor has a diagonal of just 11 mm. A full 35mm frame (24
x 36 mm) has a diagonal of about 43.2 mm, so the lens factor is 43.2 / 11 =
3.927. . . , and multiplying this by the lens's marked focal length (at the
long end) of 89mm, the 35mm equivalence works out to about 349.5mm. This is
close enough to the stated f.l. of 350mm at the long end. This is really
just doing the same math suggested in my previous post, only backwards.

The aspect ratios are different of course, the full-frame 35 being 3 : 2
while the digicam's is 4 : 3. But this doesn't really matter; it's always
the format diagonal that's used in calculations of 35mm equivalence.

Neil