Hyperfocal distance (Revere)

[P3D Neil Harrington <nharrington@xxxxxxxxxxxxx>]

Steve Owsley writes:

>I've been using a Revere 33 for many years.  I use the hyperfocal 
>guide when I focus.  Recently I got a Stereo Realist from Dr. T 
>(thanks again, George!).  I was examining the hyperfocal table on the 
>inside of the lens cap and the focusing ring of the Realist and it 
>didn't seem to correspond with my memory of Revere 33 allowances for 
>depth of field.
>
>I pulled the Revere out and examined it and compared it to the Realist 
>camera.  The Revere 33 has much more generous tolerances for allowable 
>range of 'sharp' focus at a given f stop.
>
>Both of these cameras have 35 mm lenses.  Is it possible that the 
>design of the Revere lens allows for greater depth of field at a given 
>f-stop, or is it merely that the David White Company was more 
>conservative in their computations and recomendations?

Undoubtedly the latter.

Any depth-of-field scale or table is based on some size of circle of
confusion which is necessarily rather arbitrary.

If we accept Arthur Cox's statement (in PHOTOGRAPHIC OPTICS) that the
largest circle the eye will perceive as a point at the closest ordinary
viewing distance is about .01 inch (.25 mm), then assuming a 6X viewer
(i.e., viewer lenses of about 42 mm focal length) the circle of confusion
used to establish depth of field for a Realist-format camera should be about
.042 mm.

Checking my own Revere 33, I see that the d.o.f. scale puts the hyperfocal
distance for f/16 at something between 6.5 and 7 feet.  This implies a
circle of confusion of about .037 or .038 mm, so on this basis the Revere
scale is more than conservative enough.



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