[MF3D.FORUM:583] "Toe-in, Convergence"

[narjan@xxxxxxxxxxxx]

Bill,

Most purpose-built stereo cameras, when you open the back and look in,

have the lenses closer together than the rectangular holes which determine

the areas of the film to be exposed to the image. What this does is to place

the "near point" (as calculated by J Bercovitz"s formula etc.using lens separation,

focal length, maximum allowable on film deviation, etc.)  at the same distance

from the edge of each of the pair of images, so that when you mount the images

with the "near points" separated by the same spacing as the mount aperatures,

everything from the "near point"back will appear to be at or behind the window.

Or, if you mount "for infinity" and place the two infinity points a distance apart

equal to the spacing of the mount aperatures plus the "maximum allowable on

film deviation" (usually 2.5 to 2.8 mm for medium format) then again, all items

will appear to be between infinity and the "plane" of the mount. All of the above

assumes nothing was closer than the determined near point. Anyhow, one way

to achieve the same effect using two separate cameras is to toe them in, or point

them slightly toward one another, so that the "near point" appears at the same position

in each of the cameras.

Best wishes,

John Billingham

 

(Y"all please feel free to correct this as neccessary)