P3D Re: On the "why the 1/30 rule does not work"

[Tom Deering <tmd@xxxxxxxxxxx>]

My friend George writes:

>Then he writes: "These tables assume a 50mm lens, and a maximum  on-film
>deviation of 1.2, based on the formula published by John Berkovitz. "
>
>The name is "Bercovitz" and the key word is *maximum*.  Maximum means
>"it should not be any larger than that".  It does not mean "optimum".
>The 1/30 rule ALWAYS gives less than 1.2 mm.  SO, IT WORKS.

The page in question, http://www.deering.org/basis.html, says "how to
calculate optimal separation of two cameras."  The 1:30 rule is nowhere
near "optimal" for macros, as the picture clearly shows.

We obviously are not communicating. That seems to happen here from time to
time.  Let's take this step by step, and we'll solve it.

When two cameras are too far apart, they make a stereo image that's hard to
view. Same thing happens if an object is too close, and for the same
reason.  But what point is "too close to the camera"?  What is "too far
apart"?

That's the question that these formulas attempt to answer.  And the 1:30
rule is "close enough", until you shoot close-ups.  Then it falls apart.
It predicts a number that is nowhere near the correct answer to the
question "what is too close to the camera" or, "what is too far apart."

Using George's logic, a plastic lens is "optimal" just because it "works."
You might as well use a butterknife instead of a screwdriver if you use the
1:30 rule for macros.

Cheers,

Tom



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