Re: [photo-3d] ???? Re: AF Cameras for Stereo

[Brian Reynolds <reynolds@xxxxxxxxx>]

Herbert C Maxey wrote:
> >>Indeed I'm afraid active-autofocus cameras can cross-read
> >>reference beams, yielding to TOO gross focus mismatch.  But this
> >>is a fear of my own, and I will be glad to know if somebody
> >>experienced such an inconvenience.
> 
> The simple fact is that autofocus cameras, side by side are not
> reading the same area. Please, then...explain how they can guarantee
> exact focus.  Please also explain "Cross Read Reference Beams"? I
> assume from your comment "Fear of my own ....." that you have not
> actually tested this?
> 

Some active autofocus systems use an IR beam to help the camera's AF
mechanism.  I assume he meant that there could be a problem with the
left camera focusing based on the right camera's beam due to beam
spreading.

> I understand the idea of camera manufacturers setting focus for each
> lens differently. I am away of the cameras mentioned - granted, I
> have never used either of them. I know they were not popular as the
> Realist, and I also know what the representatives for Realist had to
> say about this system.

Popularity does not mean technical excellence.  I don't think the
differential focusing scheme of the 35mm Graflex stereo camera is a
good idea, but the popularity of another system has no effect on
whether or not differential focusing is good.

> Realist stopped building cameras in part, due to the unavailability
> of quality optics that were matched.

It's just as likely that they stopped making Realists because no one
was buying them.  Several other styles of camera (e.g., TLRs,
rangefinders) have also been pulled from production (not counting high
priced collectors items like the Leicas and the Rolleiflex 2.8GX) as
their market disappeared.

I think too much emphasis is placed on matched optics.  In my own
experience (twin Lubitels, and Tominon lenses from Polaroid copy
cameras), variation in lenses isn't as great as people think.  The
Lubitels are notorious for no quality control and yet two random
cameras match for me.  I haven't bothered to measure the lenses.  A
group of us bought 12 Tominon 127mm f/4.7 lenses and the range of
variation was considerably less than one percent and pairs could be
matched to better than 0.2%.

I believe that if you stick to lenses of post-WWII manufacture from
major brands (Nikon, Canon, Pentax, Schneider, Rodenstock, Zeiss,
etc.) you won't have a problem with mismatched lenses.

> >>P.S. I prefer manual settings, so I usually use stereo cameras.
> >>but sometimes one needs a broader stereo-base, and full manual
> >>settings would hobble the use of paired cameras to non-action
> >>pics.
> 
> But the above happens rarely (I am not sure what you mean). I have
> used paired cameras. I also shoot gems and minerals, and the need
> for twinned cameras has never arisen - I use a Slide Bar for this
> work. In 30 years of Stereo Photography, the need for an extended
> stereo base has virtually never arisen. Extending the Stereo Base
> presents problems also.
> 

Your experience seems to be from macro to "normal" ranges.  In those
situations extending the stereo base (i.e., hyperstereo) would be a
problem.  I tend to go from "normal" to architecural to landscape.
For the type of pictures I take extended base is very useful.

> I know why paired cameras are used - it is because there are not
> that many stereo cameras available, or people want to try stereo
> without buying a camera such as a Realist.

Twin cameras are also used in situations where there isn't a readily
available stereo camera like full frame 35mm and Medium Format.  

> I still will maintain to my dying days, that nothing beats a Realist
> for stereo photography in its construction, lens quality and ability
> to create great stereo images.  Twin Cameras are OK, but far more of
> a hassle than using a purpose built Stereo Camera.
> 

I think you'd be surprised at the quality available from MF stereo.

The Sputnik (the most recently produced MF stereo camera) is less of a
hassle to use than a pair of MF cameras, but the trade off for ease of
use includes widely varying quality and some design problems.

-- 
Brian Reynolds                  | "Dee Dee!  Don't touch that button!"
reynolds@xxxxxxxxx              | "Oooh!"
http://www.panix.com/~reynolds  |    -- Dexter and Dee Dee
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