Re: Realist --> Holmes

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Mon, 13 May 1996 09:53:57 -0500
>From: P3D John Bercovitz <bercov@xxxxxxxxxxx>
>Subject: Re: Realist --> Holmes

>Also, I think Holmes stereoscopes have lenses of about 7" focal 
>length.  (Alan?)  The cards have an image width of approximately 
>3".  So the ratio of focal length to image width is 7 divided by 
>3 or 2.3.  Contrast that with the 5-perf: It has an image width 
>of 21.4 or so and a focal length of about 35 for a ratio of focal 
>length to image width of 35/21.4 or 1.6.  So you can see that in 
>the 5-perf format, you are sitting much closer to the image; the 
>scene is very much wider.  

No it's not. Having recently bought a Red Button Realist viewer (thanks,
Dr. T), I can say that when viewing in a Red Button and in a Red Wing
(Holmes stereoscope) viewer, the image size and the image shape are nearly
the same. (An exact comparison would require taking the hood off of my
stereoscope, and I'm not willing to do that).

Because of the magnification involved in making a 3.5" print from 35mm-format
film, I once calculated that the taking lens should be ~50mm to correspond
to the viewing optics.

I believe you've posted in the past that the Realist lenses are about 35mm fl,
and the Red Button lenses are about 50mm fl - is that correct? That would
seem to be consistent with the Red Wing and Red Button images looking about the
same.

John R


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