on 6/4/02 5:52 PM, William Sommerwerck at williams@xxxxxxxxxx wrote:
> Let me answer your question indirectly -- focal length and coverage are
> wholly unrelated lens characteristics.
>
> Focal length determines image size. A 100mm lens produces the same image
> size (magnification) at the film plane, regardless of the film format.
>
> Coverage is determined by the lens's optical construction. A 100mm lens for
> a 4x5 view camera necessarily must cover a larger field than a 100mm lens
> for a 35mm camera.
>
> Shift lenses for 35mm cameras have much wider coverage than 35mm lenses of
> the same focal length. This allows the lens to be shifted without vignetting
> the image. The extra coverage requires a much larger front element, not
> unlike the front elements of fisheye lenses. However, shift lenses are
> rectilinear. Indeed, highly rectilinear -- they have to have low distortion
> if they're to be useful.
>
> Shift lenses have been produced in 35mm, 28mm, and 24mm. You're "lucky" if
> you have enough money -- Olympus is the only company that ever made a 24mm
> shift lens.
>
The Olympus 24 Shift lens has an image circle of ~57mm... Most 35mm lenses
are designed to barely exceed the needed image circle size (~47mm) to
minimize the amount of glass and physical size needed. With a 57mm image
circle, this size image, if compressed to the fill only the 35 frame size
would be equivalent of the 18mm lens. In other words the angle of view of
the extreme left shift to extreme right shift is equivalent to the angle of
view of the 18mm lens. I think the 35 Shift has about the 24mm equivalent
angle of view. Olympus only made a 24 Shift and the 35 Shift, I think there
is a (Schneider?) 28 Shift that has been offered in Olympus mount (or
converted to fit Olympus...).
--
Jim Brokaw
OM-1's, -2's, -4's, (no -3's yet) and no OM-oney...
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