P3D Re: math-less depth charts

[aifxtony@xxxxxxxxxxxxx (Tony Alderson)]

Contradicting the use of a (Realist format) depth of field scale as a depth
range guide, Tom Deering wrote:
>Or to put it another way, the rudimentary f5.6 guess would give you 0.67mm
>of film deviation, nowhere near 1.2mm.<

This is no criticism at all of Piper's position.  If you read Piper
carefully, he recommends a limit of 0.7 mm deviation for projectable
stereo.  Personally, I consider this a conservative limit, but Charlie is
that kind of guy.  As others have pointed out, the f8 marks give
essentially the same results as Deering's curves, for ranges where the
Realist is useful.  I contend the DOF scale is more convenient for Realist
format photography, as it is already on the camera.  It is better only in
the sense that it's handier, and I can't lose it.

The observation (by others on this list, not Tom) that Realist DOF scales
vary seems almost trivial;  one has to learn the peculiarities of one's
camera.  It is rare that a consumer camera is calibrated to the Nth
precision.  Again, for pictures where the Realist is applicable, the DOF
scale is fine.

Where Tom's curves really come in handy is for slide bar, macro and twin
camera rigs.  One may have to replot the curves for few key setups, but
once done this seems quite useful.

and later, Tom continued:
>1/30, 1/25, 1/50, 1/f. Which is it? Seems like the number changes with the
>"expert."<

To paraphrase Freddie Blassie, stereo experts are a dime a dozen...and I'm
lookin' for the guy that's handin' out the dimes.

But to some extent, these shortcuts reflect different assumptions about
projectability.  Stereography is, perhaps appropriatly, more polytheistic
than monotheistic.

Tony Alderson
aifxtony@xxxxxxxxxxxxx



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