T3D Re: Deering spreadsheet

[john bercovitz <bercov@xxxxxxxxxxx>]

Dr. T suggested, regarding Tom's (or any MAOFD) spreadsheet:

> 1. Use mm for the stereo base, not inches.

I think the inch version is going to be great for most Marekins
but I agree it would be nice to have a metric version in addition
to the inch version for the rest of the world which may well have 
the majority of the stereo shooters.  I should also make an inch 
version of my maofd spreadsheets.

Side comment: Inch/metric and metric measuring tapes are getting so 
common, I think they're getting to be in the category of "out with
which no home should be".  [That phrasing may seem clumsy but you 
have to remember that a preposition is something you shouldn't end 
a sentence with.] 

> 2. Find some way to introduce magnification as a variable.

Interesting suggestion.  You mean from the object to the transparency,
not to the screen, right?  Angular magnification will be about 1 in a
proper (i.e. "ortho") pair.

> 3. Use red for any solution with under 67% overlap.

You know, the original maofd is so loaded with doodads that I didn't
want to add any more to it.  You just changed my mind.  I think the
non-overlap situation won't come up often but when it does, I sure
don't want to mislead anyone.  Thank you for pointing this out in a
way that I finally understood.  Much appreciated.

I think the warning should say no overlap unless you want to buy a
perspective-control lens.  8-)  How far _do_ those perspective
control lenses for Nikon or Canon shift?  I wonder if one of them
would be able to handle the situation you propose of a 1:1 macro 
with a 50 mm lens.  For your example, I'm showing a lens shift of 
25.6 mm as being required (relative to the camera back).  I seriously 
doubt any PC lens is going to have _that_ much shift.  The mirror
box would have to be enormous!

I'm not sure I would want to view something with that much 
convergence.  I think I might want to reduce base just for that 
reason.  After all, this is the equivalent of looking at something 
100 mm (4") in front of your face.  Sounds uncomfortable.  Have you 
tried something with these sorts of numbers by tilting the subject 
or toeing in the shots, George?  How was it?  View OK?

> 4. Spell Bercovitz's name correctly.

I can't find that error.  My name has been mispelled so many times
in so many ways I'm unsure of how it's supposed to be spelled myself.  
8-)

> 5. Omit the reference to my name (very sweet of him, but....)

Aw, George.  8-)

John B

PS: Well, I said all that and then I looked at my doodad-covered
original maofd and by golly it does have the equivalent of what 
you ask for.  Way out to the right, it says "Remaining (useable) 
chip width (window set at nearest point)".  And with your example,
I get a negative remaining chip width.  Interestingly, I get a
maximum base of 35.9 mm rather than the 50.8 mm you got elsewhere.  
Let's see what Tom's spreadsheet does.... His gives a base of 1.4" 
which is 36 mm to two significant figures.  Maybe the spreadsheet
you used has an approximation in it or maybe these spreadsheets
are incorrect.  Let me try it by geometry to see which is correct...  
Yup, I get 36 mm by geometry too.  


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