[OM] Re: Erwin Puts on the E1, Four Thirds, Olympus

[John A. Lind]

At 06:59 PM 5/28/2005, Moose wrote:

>Later, the same trick was done in reverse to put the rear node behind
>the rear element for wide angle lenses for SLRs. Notice nothing there
>says anything about the angle at which the light from the lens hits the
>"sensor". We non optical designers may assume that a lens with its rear
>element further from the sensor has light hitting it at a closer to
>right angle, but that may not be true.

The geometry of it pretty much forces this to be true . . . moving the rear 
focal point farther back forces ray paths to be less oblique.  Once past 
the rear element, a ray path is on an unerring straight line to the film 
plane.  The most oblique possible ray paths are at infinity focus.  Move 
the rear element forward (to make room for the reflex mirror) and the ray 
paths must become less oblique for the same field of view.

Another name used to describe "retro-focus" regarding _short_lenses_ that 
must be mounted forward to clear a reflex mirror in the light box is 
"reverse telephoto."

-- John Lind


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