P3D Re: Moderate Hyperstereos

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Finally!  We got Mark Dottle to post a serious message! :-)

>Unlike aerial photography where large bases would have to be 
>exponentially larger to notice a difference, don't you think 
>moderate hypers have applications requiring more than 65mm but 
>not much greater than 120 mm or so??
 
First, I don't think that the first statement is correct...
Stereo deviation is *proportional* to stereo base.  Doubling
the stereo base will double the on-film deviation.  This is
true for both aerial hypers and moderate hypers.  The exponential
effect comes from the subject distance.  Stereo deviation is
inversely proportional to the distance.  To cut the deviation to
half you need to increase the distance by a factor of 2, 4, 8, etc.
Again, this is true for both aerial and moderate hyperstereos.

On the example of the city with two trees 50 yards away... (This
is 150 feet or 1800 inches or about 45 meters).  The on-film 
deviation using a Realist (70 mm base) comes to 0.05 mm while
the on-film deviation using 120 mm base (under 5 inches) is
just 0.1 mm.  Compare this to the full stereo effect (1.2 mm on-film
deviation) which, applying the 1/30 formula, is obtained by using
a stereo base of 60 inches.

>After viewing each image, I noticed that the realist image flattens 
>out much quicker beyond the trees and the buildings appear to be on 
>the same plane (flat)  The XA2's image has noticibly more depth, the 
>buildings have distinguishable depth for 2 city blocks before flat 
>infinity. 

Yes, your observations are correct... You managed to add a little
bit of depth to a scene that was mostly flat when photographed
with a Realist.  I am tempted to call this effect "pseudo-hyper".
It might be difficult for some observers to recognize the hyper
stereo nature of the image, especially if they are not familiar
with the original scene.  But if you wanted to startle them with 
a true hyper picture, 60 inches stereo base is the way to go.

Another application of moderate hyperstereos is in combination
with a longer focal length lens, like the picture of the bear that
I had the other night at the OSPS competition.  It looked like it
was photographed with a Realist for close range (it was suggested 
that I use a flash) while in reality it was taken from much further 
away with twin cameras and 135 mm lenses and about 8 inches separation.

So, yes, moderate hyperstereos have some good applications...
I am just not sure that a *slide bar* that extends to twice
the interocular will find much use between 1 to 2 x 65 mm.

George Themelis




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