[photo-3d] Re: To math or not to math?

[zilch0@xxxxxxxxxxxx]

Hi!

--- In photo-3d@xxxx, "Dr. George A. Themelis" <drt-3d@xxxx> wrote:
> The professional's answer to unknown situations is
> "bracketing".  

I bracket my exposures +/- 1/3 stop because it's relatively easy to 
make an error in the use of my spot meter, but I do not bracket base 
separation because I'm able to measure near and far point distances 
quite accurately (with a laser rangefinder, tape measure, hand-labeled 
distance scales on my lenses.)  

These measurements not only guarantee that my base calculations are 
right first time every time, they allow me to calculate the distance 
to the plane of best focus without error and absolutely nail my DoF 
calculations as well.

Indeed, the only thing I have to bracket is the exposure, so you are 
quite right in saying that bracketing is a "professional's answer to 
unkown situations."   The part you seem to be missing is that with 
the right techniques, very little is left "unknown."

Neglecting such attention to eliminating the unknown, I would have to 
bracket for exposure, base, and to be confident, focus (DoF guessing). 
 Just doing three brackets for exposure, three for base and two for 
focus, the combination would require shooting 18 frames.  Film might 
be cheap, as you say, but time isn't.  

My calculator tells me what base separation to use to achieve the 
precise on-film deviation that I have chosen - I adjust the base with 
a metric ruler and consider this ability to deliver a consistently 
predictable stereo "bite" to be precious.  My calculator tells me 
precisely which stop will deliver sufficient DoF to yield an apparent 
7.5 lp/mm in my viewer - half again as sharp as the 5 lp/mm most agree 
is sufficient to survive the scrutiny of an audience with healthy 
eyesight.  My calculator tells me precisely where to focus - I use the 
laser rangefinder to identify a target at that distance, focus each 
camera on that target and then restore my intended composition.  There 
really is no need to bracket these parameters because I've eliminated 
the unknowns for these controls.

It feels great spending 10 to 20 minutes setting up a shot and then 
walking away with only 3 exposure made.  If using a calculator makes 
me look unprofessional, I'll just have to look elsewhere for my 
self-esteem... like in my stereo viewer.

Mike



 

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