Re: focal lengths

[P3D John Bercovitz <bercov@xxxxxxxxxx>]

Ray Hannisian writes:

> For a two camera stereo system:  
> If using a higher focal length simulates being closer to an object, should
> 'zooming in' require an increase in the distance between the cameras (to
> simulate the 'line of sight' angles for a person actually standing closer to
> the subject)?

Actually, using a longer lens doesn't simulate being lcoser to an object 
unless the object is flat.

Increasing focal length does nothing as long as you view from the correct 
perspective point.  That is, (assuming you are shooting a transparency here) 
if you increase the focal length of the camera's lenses to 100 mm and also 
increase the focal length of the viewer's lenses to 100 mm, there is no net 
effect on the reconstructed space.  However, if you use long lenses to take 
the picture and short lenses to view it, the depth will be flattened.  
Increasing the stereo base results in a "hyper" view which decreases all 
dimensions of the reconstructed space equally.  This is the giant's perspective 
on the world.

John B


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