>From: "Chuck Castleton" <ccastleton@xxxxxxxxxx>
>... I'm curious about the design issues in
>producing a large aperture lens. Is it "just" a matter of maximizing
>the diameter of the light path and removing any obstructions? Does
>increasing the diameter of the front element lead to a lower f number?
The f number is, in fact, the ratio of effective focal width to focal
length. Note that the width of the front element is not always the
"effective" focal width, as in retrofocal wide angle designs.
>... is it at least
>theoretically possible to build a 50 mm lens with a 100 mm filter ring
>and gather enough light to get to f/0.8 or something?
That would be an f 0.5 lens! I've seen various B&W utility lenses
(photocopier, for examples) with f ratios less than unity, but I think
color correction becomes more difficult, and thus more expensive, for
apochromatic designs.
: Jan Steinman <mailto:jans@xxxxxxxxxxx>
: 19280 Rydman Court, West Linn, OR 97068-1331 USA
: +1.503.635.3229
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