Posted by Les on October 16, 2000 at 21:26:27:
In Reply to: Re: 80mm W.F. Ektar posted by Bob Stoddard on October 16, 2000 at 18:19:40:
: Thanks, Les. I wonder if the data isn't really
for a small stop, even though it's stated to be
for maximum aperture. An image circle of 152mm
represents about 87 degrees of angular coverage,
larger than any of the other WF Ektars... RKS
Today lens companies give the angle of coverage of
the image circle. Back then kodak gave the angle
of coverage as two: 55°x68° (vertical x horizontal).
If the image circle covers this rectangle, then the
diagonal of the rectangle must be angle of coverage
of the image circle. So A squared + Bsquared=c
squared
That's how I came up with 87°. Now if you draw an
x with the lens at the vertex then the top and
bottom angle is 87°. It's 80mm from the vertex to
the film plane. If you draw a perpendicular line
from film plane to the lens you will end up with a
right triangle with a 43.5° angle at the top (the
line bisected the angle of coverage) and one
known side of 80mm.
Machinery's Handbook says you can find the opposite dide (or half the image circle diameter) with the formula b= tanB*80mm. for the diameter multiply by 2.
Now exactly what Kodak meant by 'maximum aperture'
does have me confused. Why would anybody want to
know this info at wide open?