P3D Re: stereo base

[koganlee@xxxxxxxxxxxxx]

        I have done my best to stay out of this discussion about stereo base, 
but I can't resist putting in my 2 cents after reading Bob Maxey's 
statement,

"Now, suppose that the stereo base used goes against all of the conventional
wisdom the whiz Bangs are proffering. How would I be able to tell if one of
the images is really bad, because I used the wrong math?"

You'd be able to tell if one of the images is really bad by looking at 
it. The whole point of using any system for deciding on a stereo base is to 
get the best image possible. If a formula or system is not giving you a good 
result then either it is wrong or you aren't using it properly. Ideally one 
would try variations of stereo base for every image, and then judge the 
resulting images to see which worked the best. The concept behind this is 
just like bracketting for exposure when you want to get exactly the best 
exposure (you don't get it with the f16 rule or with a light meter, you get 
it by varying the exposure and looking at the results). It's the same as 
looking at test strips or ring-arounds when you're making a print. There are 
all kinds of expensive analyzers, but the only real criterion is the final 
print. I don't normally make variations of camera separation anymore, 
because I have done it in the past and am relatively confident of getting 
what I want. I did make an exception to this while I was driving to the 
convention in Richmond (from California), though. I stopped at Mt. Rushmore 
and made some exposures. First I decided on my best estimate for camera 
spacing based on my prior experience. Then I decided to vary the camera 
separation by making additional exposures using half that distance and twice 
that distance (kind of like bracketting exposure). The interesting thing is 
that all of them are quite acceptable, but the short separation was a little 
flatter than I would have preferred while the long separation was a little 
deeper than I would have preferred, with my original estimation looking the 
best. Generally speaking a wide range of variations will give "acceptable" 
results, but I am looking for excellent results, not acceptable results. 
        My advice to a beginner would be to vary the separation until one has 
enough experience to know they've got what they want, and the only way to 
get that experience is by doing the ground work. If the formula doesn't give 
you what you want, it is (by my definition) wrong. Formulas are made to help 
give you a good result, but they are not the result themselves. If a person 
has a formula that gives them a result that they like then they should use 
it. Personally I use intuition based on years of experience and looking at 
the results of varied separations based on a formula which I will be glad to 
explain to anyone who wants it. While my ideas are based on a formula, the 
formula is just a tool, while the image is the only thing that matters.
        On another note, I will mention that I friend has asked that I send 
her a box of my recent stereo cards. I will be happy to send them to anyone 
else that would like to see them. The box will include at least 3 Best of 
Shows from PSA stereo card (I don't do slides) competitions. Just email your 
mailing address to me and I will put you on the list. I will also include a 
stereo card viewer in case someone doesn't have one.

David Lee
koganlee@xxxxxxxxxxxxx



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