P3D Re: Single SLR Macro 3-D - Part II

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Sun, 29 Mar 1998 15:33:32 -0700
>From: Larry Berlin <lberlin@xxxxxxxxx>
>Subject: P3D Re: Single SLR Macro 3-D - Part II

>>Date: Sat, 28 Mar 1998 
>>From: "Andrea Blair" writes:
>>but all of my shots are like this and are viewed perfectly. If someone 
>>would like to explain this to me, please do. I don't know WHY it works, 
>>I just know it WORKS!*** 

>*****  It works because ... First of all, you are accurately describing your
>work environment and movement directions. It makes sense that starting with
>the Right image you will have most of your subject somewhat to the left of
>center, and that this reverses when you move to the left image. What
>confuses certain others is a misapplied rule of thumb. It has to do with the
>fundamental geometry rules relating to the stereo window. You are working in
>front of the stereo window so nothing reverses or crosses over. 

Good explanation! (I hadn't figured it out yet.)

>>Now for the extremely tricky technical part of 
>>how far to move the camera each time. Based on the camera to subject 
>>distance ratio (do I need to move to Tech 3-D at this point {:>) ?), the 
>>answer is......about that much. What? How much? Did you miss it? I'm 
>>sorry to disappoint a lot of you "techies," but I don't have a formula. 
>>I just let the picture "happen." That's why I take more than two shots. 
>>I can match the best two images which give me the best 3-D view. 

>*****  In making multiple images it is more important to be consistent in
>the amount you move each time than in precisely how far you moved. The
>results will speak for themselves. I use a similar technique and the
>dependence on a developed sense of the right distance is far more useful
>than a calculator.

I took a large number of macro stereo photos in a short period of time several
years ago (and none since then, but I still have the equipment). I found
that the subject matter and the internal geometry of the scene appeared to
affect the "optimum interocular for a pleasant stereo pair" much more than
any sort of fixed "one in thirty" rule. Perhaps if there had been more photos,
some sort of more general rule would have become evident, but I just stuck
with multiple images, like you and Andrea have done.

I tried to use sequences of interoculars to maximize the probability of
good results - for example, if I had no idea of what would work well, I
might try 1mm, 2mm, 4mm, 8mm.... If I had a closer estimate, I would use
a sequence intended to produce two or more good pairs, with bracketing of
interocular for each.

With the range of magnifications I used, I never came across a situation
where a "granularity" of less than 1mm provided any great benefit.

I don't know the characteristics of Andrea's camera, but the Minolta X-700
has some very nice features for macro work:
 - In autoexposure modes, it always takes a final reading after stopping
     down, etc., so those formulas for exposure compensation with extension
     tubes, etc. aren't really necessary.
 - It uses through-the-lens (TTL) flash exposure control, so a remote flash
     could be employed.

John R
(Hoping Andrea can be persuaded to demonstrate her macrostereo techniques)


------------------------------