[MF3D.FORUM:595] Re: "Toe-in, Convergence"

[Michael Kersenbrock <michaelk@xxxxxxxxxxxx>]

> narjan@xxxxxxxxxxxx wrote:
> 
> 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. 
~
> 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.

This will be a similar effect, but I thought I'd mention about how it's
not really the same.  The exposure-window offsets in cameras such as the
stereo realist puts things at a given distance (7' as I recall) at the
window when the film chips are mounted "straight", "as is".  It's exactly
the same as if one had the openings directly behind the lenses but you then
trimmed the inside edges of the film chips a bit afterwards -- except that 
the result would be a slightly narrower net film size due to cropping (vast
majority of the film "opening" is in exactly the same place, without regard
to where the edges of the opening are, so the image there is identical to 
that where the openings aren't moved).  
So it's an a "efficiency" thing for "commonly" expected photographs.  

Toeing-in the camera lenses instead does provide "efficiency" of film-chip
too, but does so at the cost of image distortion (keystoning).  Not that 
it's significant or not a good idea in practice, but only to say it's not 
exactly the same thing.  The lenses in the Realist are exactly parallel.  
In my RBT X3, for instance, lenses are parallel too, but the
image areas are not offset, so I have to offset in the mounting process,
and I lose more and more as the close-in subject gets closer and closer
(mounting to the window).

It's set to infinity by default.  I suspect my Sputnik's are too.  True?



Mike K.




> Best wishes,
> John Billingham
> 
> (Y"all please feel free to correct this as neccessary)