To answer the questions about the rear nodal point (which I was improperly
calling the exit node)...
If I correctly understand the literature, the distance from the rear nodal
point to the film plane _determines_ the lens's focal length. Changing the
position of the rear nodal point changes the lens's focal length. There is no
way you can "compensate" for this.
In a "simple" lens, the front and rear nodal points are near the physical
center of the lens. The "trick" with telephoto and retrofocus lenses is that
the nodal point can be moved towards the front of the lens (thus making the
lens shorter than a conventional "long" lens would be) or towards the rear of
the lens (thus allowing the lens to sit far enough from the film plane so the
mirror doesn't bang into it). The nodal points don't even have to be "inside"
the lens -- they can be in front of or behind it.
With respect to the lens in the XA... According to the articles in issues #10
and #11 of Olympus VisionAge, the XA was to be absolutely no more than 4cm
thick. Using a conventional lens design, the focal length could be no more than
31mm, which was too short for general photography. A 35mm lens would have to
sit 4mm farther from the film plane, making the camera too thick and ruining
its aesthetics.
After a lot of agonizing, the lens designer suddenly realized that a telephoto
design would move the rear nodal point far enough forward to make a 35mm lens
possible. But 35mm is wide-angle, and you didn't use telephoto construction (a
positive group with a negative group behind it) for wide-angle lenses!
Well, yes you do, if it works. It did, and you know the rest of the story --
the XA was one of the most-successful pocket cameras of all time, and still
commands a good price. We have here a good example of Dr. Land's dictum:
"Creativity is the sudden cessation of stupidity."
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