P3D Re: Stereo base formula: Please help

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Mon, 15 Mar 1999 07:46:33 -0700
>From: Dogbreath <hopi@xxxxxxxxxx>
>Subject: P3D Stereo base formula: Please help

>Could someone please refresh my memory on the formula stereo photographers
>use to calculate the length of the stereo base when using a single-lensed
>camera (ie, a 35mm SLR)? For example, if I'd like to shoot a macro stereo
>pair using a 50mm lens and my subject is ten inches away, how would I
>calculate the appropriate distance to slide the camera from the one side of
>the base to the other? I've read the simple 1/30th rule, but that doesn't
>seem to take the focal length of the lens into account (or, if it does,
>it's based on the 35mm lens of the Realist and other 5 perf cameras). Are
>there any limits? Is there a point where the formula fails? 

The people who calculate the formulas are all on T3D (and some of them
are not on P3D), so you will get better answers if you post your question
there.

For macro, both the nearest and the farthest object in the field of view
are very important, as well as the focal length of the lens. Using a 50mm
macro lens and with the photographic subjects I've used, I generally find
that I like *less than* 1/30 best. Two possibly useful rules of thumb:

1) Since you mention having an SLR, just look through the viewfinder as you
move the camera. The spacing at which you just barely notice a shift in the
relative positions (not absolute positions) of the objects in the field of
view might be a good starting point for a test shot.

2) If you're willing to invest in macro equipment, you're not talking about
extreme low-budget photography anyway. Instead of just two shots, take a
whole series of shots, documenting the position of each one, then check the
stereo of different pairs from this series, and find out which spacing you
liked the best. (This will probably vary from subject to subject.)

John R


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