T3D Where?

["Andrea Blair" <asblair@xxxxxxxxxxx>]

>>>>john bercovitz writes: I hope I'm not presuming too much when I 
presume you mean for the MAOFD spreadsheet.  If this is the case, you 
want to measure from the front principal point unless you have a highly 
asymmetrical lens in which case you don't want to deal with it, believe 
me.  (See the perspective paper Tom Deering put up on his web site for 
details if you're a masochist.)<<<<

Actually, I haven't even looked at that yet! I'm waiting for when I have 
a LOT of time to study it in depth...er, in great detail. {;>)

So, from what I'm reading, what you're saying is there is no *easy* 
answer for macro (anywhere from 4:1 to 1:1 and closer). When I started 
doing stereo I was told an easy rule-of-thumb is 1:30. Nice until I'm 
right on top of my subject. Then the starting point for measurements 
becomes much more critical; actually imperitive. I am trying to write an 
article (and update my slide program) on stereo macro with one SLR. It's 
easy for me, because I don't bother with formulas (cover your eyes, 
Tom!) and just move the camera and take 3 images. I match the best two 
for the stereo pair. I don't mind telling people I do this, but I would 
like some sound information that can be used as a guideline. This would 
also preferable be something easy, as opposed to pointing a light into 
every lens to measure focus points.

What happens when I add a tube between the lens and camera. How about a 
close-up diopter which now allows the lens to be closer to the subject? 
How about both? I also have a focusing macro doubler (from Vivitar). It 
turns a 50mm lens into a 100mm macro lens. What happens then?

I'm so confused! {:>(

Maybe I should just stay formula challenged and let you math gurus 
explain it to everyone!

Andrea Blair
asblair@xxxxxxxxxxx

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