Closeup lenses

[T3D Michael Gordon <mgordon@xxxxxxxxxxxxx>]

I do not believe there is a significant change in focal length using a 
closeup lens, since the main lens will be set at or near infinity, the 
closeup lens simply causes the 50 mm lens to "see" something nearer than 
it really is.  Without the closeup lens, you'd have to use a bellows or 
extension, and then you increase the focal length and change the F-stop. 
 So, the effect of the closeup lens is simply to keep the focal length 
and f stop the same, while getting closer; and in my opinion would not 
affect the formula for separation at all -- the point of optical 
crossover (the virtual pinhole) will still be 50 mm away from the film 
plane and that is what is important to the geometry of the equation.

Sincerely,
Michael Gordon


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End of TECH3D Digest 58
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