P3D Macro

["Andrea Blair" <asblair@xxxxxxxxxxx>]

>>>>A few days ago (before the BIG EVENT), Andrea Blair wrote: In 
response to Michael Georgoff's rather lengthy post on stereo base and 
where the measurement to the subject starts from, here's the responses I 
got:

1) The film plane
2) The front of the lens
3) The middle of the lens

Go figure!<<<<

Add: 4) The nodal point of the lens (whatever that is), which tends to 
change as the lens in cranked in or out, from what I'm told.

Now, forget everything you've read so far on the stereo base for macro. 
There is none. Sorry folks. I have come to the conclusion, after talking 
with several folks and attending an excellent workshop by David Lee, 
that there is in fact no (at least no easy) mathematical calculation for 
the stereo base for macro. I'm sure there may be some obscure string of 
figures that requires a scientific calculator, a slide rule, and a an 
abacus to calculate, but don't send it to me - I don't care. David 
reinforced the basic principal I have been using all along - trial & 
error and personal preference. Where I usually take three images per 
set-up, David takes four. He has even worked out a very simple rule of 
thumb:

1) Decide what the total horizontal distance you will move is
2) Divide this number by X (his example was 6, you can use any number)
3) Take four shots: one at 0, 1/X, 4/X, and final distance.
4) By using these four shots, you can match 6 pairs to find the one (or 
more) that you prefer.

Example:

1) If you want to move a total of 48mm, divide by 6 (X).
2) The first pic would be at 0 (shot A)
3) The second pic would be 1/6 (in this case) or 8mm (Shot B)
4) The third pic would be 4/6 (in this case) or 32mm (Shot C)
5) The fourth pic would be the last measurement or 48mm (in this case) 
(Shot D)

A + B = 8mm
C + D = 16mm
B + C = 24mm
A + C = 32mm
B + D = 40mm
A + D = 48mm

So easy!!!!

By the way, David measures from the front of the lens to the subject. I 
think this is used to establish a rough 1:30 as a base, then he applies 
the above calculations.


>>>>Mark Shields wrote: Oops! I should have said "macro on a slidebar" 
instead of "macro on a focusing rail"--I tend to think in terms of what 
I use--I have an old focusing rail that I turn sideways for macro shots, 
instead of a "real" slidebar.  :-)<<<<

For precise minute movement in macro photography, a macro focusing rail 
(which has tension screws, turning knobs, and a ruler) is much easier to 
use than a slide bar. If you do a lot of macro photography, I would 
recommend one. They come in either single (one way) or dual (two way - 
horizontal and forward & backwards). They are very handy, but 
unfortunately, not cheap. I have not seen any second hand that I can 
recall.


>>>>Bruce Springsteen (not the Boss) wrote: Andrea's question about 
where to measure from was on my mind too.  I only have a 35-70 zoom on 
my SLR and was foolishly measuring from the foremost lens to the near 
point on my main subject - 15 inches.  I took a series of shots in this, 
my first close-up tabletop attempt, beginning with the 1/2 inch (1/30th) 
base, then increasing 1/2 inch for each succeeding shot, perhaps up to 
2.5 inches.  The pairs that finally pleased my eye were more like 1.5 to 
2 inches base, FL on lens near 50, so I have no idea what happened.  
Which I guess puts me for now in the "don't worry, shoot happy" class.  
But it's an uneasy state.<<<<

Forget the math. Don't Worry, Shoot Happy!

Andrea S. Blair
asblair@xxxxxxxxxxx


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