P3D Re: Tom's Base Calculator

[Bruce Springsteen <bsspringsteen@xxxxxxxxx>]

Tom Deering wrote:
> I've been having an off-list discussion about the 1:30 rule, and how
poorly
> it works for macros.  To help the discussion, I have placed several
charts
> on my website that show the Berkovitz geometrical calculations for
maximum

[excision]

> Maybe you could print these two tables, and put them in your camera
bag.
> Then you could have access to good math, almost as easy as the 1:30
> estimation.

[another excision] 

> http://www.deering.org

Now this is the kind of pragmatism that I hoped the erstwhile
base-math cheese-nibbling discussion would lead to.  So let me wade
back in with some (possibly obtuse) questions.

It appears that Tom has used Special Case #1 from the Bercovitz/Spicer
article on base calculation.  That is the recipe that maximizes depth
of field by making the near and far points equally unsharp (assumes no
infinity in picture).  In getting from the "general" solution to this
one, the article takes the intermediate step of calculating the focus
point that achieves max DOF, and assumes you will focus there.  If you
use Tom's macro/closeup charts *without* doing the calculation for
that focus setting, are you losing the geometry that makes this
equation work?

Bercovitz/Spicer's Special Cases 2 and 3 both assume a far-point at
infinity.  Case 2 again maximizes the depth of field, while Case 3
focuses on the subject near-point, a likely choice for close & macro
work I would think.  But why no Special Case for focusing on the
near-point, with a far point *not* at infinity?  That's the situation
I most likely would be in on my tabletop, or in a think-fast and shoot
situation.  What have I missed?

The rectangular charts at Tom's site are fairly easy to use (at least
if you aren't color blind or have a non-color printer - light limey
green indeed!).  But my wish has been for a circular calculator wheel,
like the proportional scales used in printing and art.  Align near
distance on the inside wheel with far distance on the outer wheel (up
to infinity?) and read the maximum base - or a range of bases -
through a little cut-out in the small wheel.  A given wheel would
assume one format/maximum on-film deviation (1.2mm for 35mm).  Don't
know if one wheel could have answer several windows for different lens
FL's or if it would be one focal length per wheel.  Has this been
done?  Is it feasible?  Which formula would you use?  Again is the
focus point an issue?  Where's the rub?

Why'd Tom use inches instead of metric in his distance numbers?

Who's got the savvy to set me straight?  Will I be exiled to Tech3-D
for this impertinence? ;-)

Bruce (Dining on Macros & Cheese) Springsteen

PS - My Weltanschaaung is much better now, thanks for asking.

 




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