With little trepidation, Rodger Whitlock opined on 02/11/2001 06:41:
>On Sat, 10 Feb 2001 at 18:47:50 +0000, Clive Williams
><[EMAIL PROTECTED]> wrote:
>
>> What I don't understand, Inspector, is how a 71mm-wide disc of light
>> can pass through a 50mm-wide hole.
>
>To give you a *very* simple example, do the thought-experiment
>punching a hole in the back of your camera. See that 60 story office
>building over there? Its image will go through that hole (with the
>right lens, of course!)
>
>Thus it is no trick to getting an image of that 71mm diameter front
>to squeeze through the throat at the back.
>
>QED (maybe -- I may have committed a logical fallacy somewhere and
>cooked up an example that demonstrates some other principle
>entirely.)
The same way a 10mm arc of electrons in a theatre projector can spread
out to fill a huge screen. Optics.
Remember they told you the image on the film was upside down relative to
the subject? (those who've only used SLR and rangefinder cameras would
not know this from a practical point of view) Well, at some point in the
light path through the lens, all those rays must cross over on their way
to the film. At that point, the throat of the lens can be very small.
Take a look into your wide angle lenses if you want to see it. The light
then spreads out to hit another set of lenses that focus the light at the
film plane.
JoMac, Imagineer with Camera
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