In telescopes and binoculars the image is allowed to fall wherever it
may and focus is accomplished by moving the eyepiece. To use the same
system in a camera the focal plane would have to move (a lot) and also
be physically tied to the eyepiece movement. Much simpler for both sets
of optics to focus on a fixed position which is the view screen whose
optical path from the body flange is the same distance as the
film/sensor plane.
The OM 1-9 type screen for endoscope use is a clear screen but it can
only be used with an endoscope attached since no focusing is required.
Chuck Norcutt
Moose wrote:
> usher99@xxxxxxx wrote:
>> ...
>>
>> Moose and Chuck hit the nail on the head a usual.? I ran across an article
>> which I excerpted below on focussing screens and manual focus:
>>
> Thanks for the info, a nice write-up.
>
> Now for something to chew on. Why is a view screen needed at all? Why
> not focus on the aerial image as do microscopes and telescopes?
>
> The answer shouldn't too tough to figure out.
>
> Moose
>
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