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Re: [OM] f/0.x lenses

Subject: Re: [OM] f/0.x lenses
From: "Tom Trottier" <TomATrottier@xxxxxxxx>
Date: Sun, 14 May 2000 03:08:48 -0400
Hi Jan,

Also, different lenses transmit different percentages of light. The 
most obvious example of this is mirror lenses because of the 
obstruction, and zooms, with all their glass/air surfaces.

In the movie biz, they being very sensitive to light changes within a 
scene, and between scenes and lenses, use a "true stop" or "t/stop" 
which is photometrically accurate.

BTW, I have used an f/0.95 lens. On a movie camera.

Tom

At 2000 May 12 - Friday 9:06, Jan Steinman <olympus@xxxxxxxxxxxxxxx> 
spoke about *Re: [OM] f/0.x lenses...* saying

> >I always understood the f number to refer to the ratio of the actual
> >scenery light intensity appearing inside a lens.  Ex: f2 would let in
> >1/2 the light intensity.  Ergo, wouldn't f < 1 imply that light
> >amplification was taking place.
> 
> Not quite. "f" is the ratio of focal width to focal length, and 
> depending on the lens, may have little to do with the actual light 
> coming through.
> 
> When you adjust the diaphragm, for example, you are changing the 
> focal width, and thus the ratio.
> 
> So a 50mm f0.5 lens, for example, would have a 100mm focal width.

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