Archived posting to the Leica Users Group, 1997/02/18

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Subject: Re:Pinhole aperture info
From: Soon Wai Hoe <adisoon@pl.jaring.my>
Date: Wed, 19 Feb 1997 00:41:19 +0800

I tried piercing a hole in a Leica bodycap but the diameter of the image
circle was only the breath of the negative. What should I do??

- --Adi 

At 10:40 PM 17-02-97 EST, you wrote:
>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
>
>