1. Daniel Mitchell wrote:
<< why isn't the 16mm f0.6? Is it some sort of coincidence that 50mm happens
to match up with the least amount of glass and that's why it's the "standard"
lens? >>
I would guess that the 50mm lens is the easiest lens to make for 24x36mm
image 35mm film, which needs an image circl to be at least about 44mm to
cover the entire film.
Imagine making a bigger f/2 lens say 250mm. You could just scale the 50mm
lens up by 5x in every dimension, and then you would have a lens suitable for
film which is more like 120x180mm. But the aberrations would be scaled up too
and you might not get much advantage with this extra film size and it might
be a bit heavy. Of course, diffraction problems would be much less at this
size, but would be swamped by aberrations (spherical and chromatic) I would
guess.
But the Zuiko 250/2 is designed for 24x36 film again, with the same 44mm
minimum image circle, so you will need the same high resolution in absolute
terms as a 50mm lens, even though you have much bigger lens elements and
greater distances and image magnification and aberrations will be magnified a
5x basically! It's a big challenge to get 100 lines per mm resolution or
whatever with such a big lens I would think!
Medium Format standard lenses are what(?) 85 or 90mm or so for film about
twice the dimensions at 45x60mm or whatever. These lenses are often slower
than 35mm film lenses it has been mentioned before. Maybe the fact that you
want the resolution to be the same in absolute terms as for 35mm at say 100
lines per mm and you don't want aberrations scaled-up in size, gives a
greater restriction on the speed of the lens.
With the small focal lengths, you have the problem with the need for
retrofocus design with SLR cameras because the lens can't be less than an
inch away from the film without smahing the mirror! So your 18mm ultra-wide
can't be 18mm away from the film! Also, I would think that these lenses have
big problems in getting the light coming from widely differing angles
projected onto a flat film plane, keeping straight lines as straight lines
(rectilinear) near-perfectly. This also corresponds to a problem of making
the lens' image circle BIG enough to cover the 24x36 film entirely. With the
8mm fisheye, it doesn't!
If you reduce the size of the film to half-sizes, say 12x18, it would
probably be easy to have a 25mm F2 lens. That would be equivalent to a 50mm
F2 lens for Olympus OM. You could go smaller and smaller but diffraction
problems increase as you go smaller and making the parts precise when they
are so tiny would also be a problem.
But it sounds like a fun and interesting job to have!
...
Dave Bellamy.
http://members.aol.com/synthchap/
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