[photo-3d] Re: Depth ranges

[abram.klooswyk@xxxxxx]

Paul Talbot wrote:
> According the John Bercovitz article "A Comparison of Camera Base
> Calculation Methods" http://home.mira.net/~kiewavly/bases.html the
> definition of "an" (near point) as used in the stereo base formulae
> is: the distance from the lens center to the near point in the 
scene.
> I trust John B. to have that right, but I haven't "proved" it 
myself.
> The article doesn't mention using a bellows, so I don't know whether
> that would require any modification.
             (Dear Paul, your lines are too long...)

John Bercovitz used the lens center, instead of the principle 
points, for easier clarification, I believe. The difference is 
mostly neglectable. The formula automatically takes care of 
bellows or indeed of any focussing extension, because the 
extension follows from camera lens focal length and focusing 
distance (the lenses formula, this is also explained in the 
appendix of the article).

However, John Bercovitz presumes that viewer focal length is 
equal to "working" camera focal length. So be prepared to buy 
a set of different stereoscopes and sort your slides according 
to focal length. 

David Kesner:                  
>RBT X3A with an RBT Macro Attachment. The lens is 105mm 
>and the stereobase is 11mm. The magnification is  close 
>to 1:1 in this image. 

A 1:1 magnification means a bellows extension equal to the 
lens focal length, so a "working" focal length of 210 mm. 
According to the Bercovitz doctrine you should buy a 
stereoscope with 210 mm focal length lenses.

(Sounds strange? I agree.)

Abram Klooswyk                             








 

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