Archived posting to the Leica Users Group, 1997/02/17

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Subject: Re:Pinhole aperture info
From: photology@juno.com (Thomas P Myro)
Date: Mon, 17 Feb 1997 22:40:53 EST

Good Day!

I just looked through some of my older Zeiss microscopy catalogues, and
have read Dr. Abbe's theory of numerical aperture.

The numerical aperture of any lens is calculated by dividing the focal
length of the lens by the RADIUS of the physical aperture--1/2 the
diameter of the hole, in mm.
in regards to the pinholes.

The focal length of the pinhole has nothing to do with its apeture, but
rather it is the distance from the film plane to the aperture. 

So:  a pinhole located 50mm from the film plane IS a 50mm lens, a pinhole
located 100mm from the film plane is a 100mm lens etc.  

Apertures at 50mm extension:

0.25mm hole--f400
0.5mm hole--f200
1mm hole--f100

f100 at 50mm extension, should yield depth of field of approx 2" to
infinity.

I hope this helps all you "Pinholers" out there.

Sincerely,
Thomas P. Myro
Photology@juno.com