Well, consider this. The mirror must be at a 45 degree angle to bounce
light up to the pentaprism. That would make the mirror take up about 50 mm
in front of film plane. That means the closest that any lens in an SLR
design could get to the film plane is 50mm + some safe distance.
Now consider what the "14mm" focal length in a "14mm fisheye" lens means.
That means the distance from the central focal node to the film plane. Now,
most SLR lenses use retrofocus designs to do some magic to make this
central node actually *behind* the last element of the lens because they
can't get close enough.
But in a rangefinder, there's no such need to be worried. The rear element
can almost graze the rear shutter. Lens designs can be simpler,simpler
designs often have less problem with flare, they weigh less, they use less
$$$ material, and for some reason still cost $2000+ for a 50mm design just
for the privilege of the "Leica" badge.
Note that once your focal length exceeds about 80mm, there really is no
advantage to the rangefinder design, since the back element would clear the
mirror (if one existed).
Karen
At 8:38 AM +0700 2/14/01, Innoyen wrote:
>Dear list,
>
>I recall that range finder design of no mirror makes it possible to attach
>the lens with its rear element very close to the shutter. This, I was told,
>benefits the design of wide angle lenses. As such we have Hassy SWC, which
>is a body designed for the lens, and probably that's why rangefinders such
>as M6, G2 and Hexar are still in demand.
>My questions:
>What really is the benefit of being able to put lens as close as possible to
>the film (shutter)?
>Is it simplicity of designing the lens or is there a natural law prohibiting
>certain quality if the lens is placed longer than certain distance from the
>film?
>
>
>Innoyen
>---------------------------
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