In article
>BRIAN PETER MERRY (002846m@axe.acadiau.ca) wrote:
>: I now know 20mm is 94 deggees (d), 18mm is 100d and 16mm is 180d.
>: Where does the 17mm fit in here?
>: Brian
> What's confusing you is the non-linear
> scale that jumps to 180o. That doesn't
> belong on that scale. 180o would be a
> fisheye, which can't be compared to a
> constant magnification lens such as a
> regular wideangle.
>
> Fisheyes vary their magnification as you
> move away from the axis. They are about
> like a 28 on axis, an 18 1/2 way out, and
> a 10mm near the corners.
[rest of nice post deleted, to nit-pic what remains,
since DR doesn't often make such mistakes! ;-]
A 16mm is a 16mm on axis, whether its perspective is fisheye
or rectangular, and the image size is the same in the center
regardless of lens type - but the size does change with
angle off center in the fisheye type, as David said.
Hope This Helps