Correctly Calculating camera closeness

[P3D <GCCampos@xxxxxxx>]

I found this in the archives and thought the new people would benefit from
it.

<< John B. derived the following equation, which I think everyone agreed was
      
 more accurate than earlier attempts we'd heard of:
                             




                                                                             
 B = d * ( f * ( an + af ) - 2 * an * af) / ( 2 * f * ( an - af ) )
             




                                                                             
 where B is the baseline, d is the maximum desired deviation in the
             
 negative, f is the focal length, and an and af are the distances to the
        
 near & far objects, respectively.
                                              




                                                                             
 This is a bit ugly, but in the limit as af goes to infinity, it simplifies
to:  




                                                                             
 B = d * (an/f - 1/2)
                                                           




                                                                             
 which in turn is very well approximated by:
                                    




                                                                             
 B = d * an / f.
                                                                




                                                                             
 The part where personal perference comes in is in the choice of a value for
    
 d, the maximum on-film deviation.  The classical value (if I remember
          
 right) is about 1.5 mm, though personally I prefer something a bit larger.
     




                                                                             
 Someone had tabulated values for the various equations & could probably say
    
 when af was reasonably close to infinity.  I don't remember who, though.
       
  >>

I've got this programmed into my HP15C but haven't used it yet.

Have Fun
Grant :)


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