T3D camera focal lengths

[john bercovitz <bercov@xxxxxxxxxxx>]

Depending on the end viewing method, the focal length of the 
camera's lenses should be varied to prevent stretch/squash, 
if you're concerned about such things.  

For 35 mm cameras, St. Ferwerda 8-) recommends 70 mm lenses 
if the result is to be projected.  Since the image area of 
35 mm film is about 24 mm high, what he is saying is that 
the average audience member is sitting 70/24 = 2.9 times the 
projected image's height away from the screen.  For a 4' 
screen (and 5P) this would mean sitting at a little less than 
12' from the screen, a very reasonable estimate.

I think one of the nicest setups for images seen in a hand 
viewer would be 50 mm lenses on the camera and Edmund's 6X 
(50 mm) #42769 at $80/copy.  

And this brings us to RBT cameras.  There aren't any fixed-
focal length 70 mm lenses on the market that I am aware of 
but one option on an RBT is a zoom which includes 70 mm.  
Another option is fixed 50 mm lenses of good quality which 
ought to be great in a hand viewer.  But getting back to the 
zoom lens, what is the distortion like at 70 mm?  I wouldn't 
be very interested if the distortion is more than 1 or 2%.  
Anyone have one of these things?  Anyone tested it?

Thanks,
John B


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