P3D Re: Hyperfocal Tables

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Gabriel writes:

>Humm, sorry Dr.T, but the case was solved over a year ago! :-)

Thank you Gabriel!  You just wasted 15 minutes of my valuable time! :-)
Here is what you wrote in Digest 2578:

>wondered why there were differing tables and the conclusion was 
>because the CoC parameter was probably changed. 
                               ^^^^^^^^
That's no mystery solving... It is just a guess.  A guess that
turns out to be correct :-).  But I confirmed that this is inddded
the case from offical Realist documentation.  So, *I* solved the
mystery! :-)

Now, why did they changed (increased from 1/750 to 1/1000 in.)
the circle of confusion?  Gabriel speculates:

>Now one would think that they would decrease the CoC for the DW
>lenses, since they are supposedly not as sharp as Ilex lenses but
>we see the opposite. From all this it would seem to indicate that
>it was done for purely marketing purposes.

The only considerations in selecting a value for this "circle of
confusion" are the resolution of the film and the viewing conditions.  
Not the lenses of the camera but the lenses of the viewer!  So it 
would make sense to say that they reduced the circle of confusion 
because they now use lousy lenses in the red button viewers! 

I am quoting from "Realist News 1.4 (Oct. 1951):

"The Hyperfocal Table figures quoted in this article indicate 
somewhat greater range of sharpness shown on the table on the
camera.  The new table is calcuated using a 'circle of confusion'
of 1/1000 of an inch.  The new table is calculated using a
figure of 1/750 inch and is more than sufficient for any stereo
viewer."  (Shortly after this the Tables were changed in the cameras)
^^^^^^

Rudolf Kinglake in the "Optics of Photography" lists suggested
circles of confusion for different film formats.  For 35 mm he
uses 1/750 in.  (larger film formats use larger CoC as expected
because the magnification will be less to view these).

For those interested in projection the CoC should be much larger
because the resolution in stereo projection is much less. 

George Themelis


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