P3D Re: slide bar

[George Gioumousis <georggms@xxxxxxxxxx>]

Steve Berezin wrote
> 
> Dr. George A. Themelis wrote:
> > 
> > Steve Berezin asked me to elaborate on this:
> > 
> > >Moderate hyperstereos (in the order of a few times the normal 65 mm)
> > >in my opinion are pretty much useless.
> > 
> > I know it sounds very provocative as a statement, but here is my
> > reasoning:  Our eyes are spaced on the average 65 mm apart.
> > There are many situations where we would like to shift the camera
> > less than 65 mm.  Close-ups, macro stereo, excessive depth in the
> > scene, etc.  I cannot think of any practical situation where 120 mm
> > would do it, while 65 mm would not.  Can you?  If the subject is far
> > away and a hyperstereo is needed, usually this would be quite a few
> > times the average interocular and not just two.
I don't quite see this. Let me try an analogy: Back in my early days as
a photographer all I had for close-ups was a 3 diopter filter-like
gadget. It _was_ better than nothing, but my present setup that varies
continuously from infinity to one-to-one is much better.
> 
> I agree 120 mm is not much.  The home made drawer slide slide bar I
> cobbled together however can do hypers of 30 to 40 cm's in seconds. It
> can also accurately do a few mm. I think some other drawer slides can
> extend to 60 or 70 cm with a very smooth action. All that is needed is a
> drawer slide, a 1/4-20 T-nut, a 1/4-20 bolt and a couple pieces of wood,
> (if anybody is interested I can put the plans on a web page).
> 
> -- 
> Steve Berezin
> mailto:steve@xxxxxxxxxxx
> 
There are several ways of arranging for hyperstereo. A real odd-ball gadget
was a Spiratone tripod I got during my first incarnation as a stereo 
photographer. The center post could be tilted to a horizontal position, thus
forming a combined slide bar and tripod. Spiratone no longer sells this,
but some years after I bought mine I saw a Velbon tripod that was identical
except for nameplate. I haven't seen this one either recently.

A while ago I build an all-wood slide bar that works quite well. Most 
people can't quite see why it should work, but are able to see that it 
does work smoothly. John Bercovitz said "Ah, kinematic design" when he
saw it. My former boss was a mechanical engineer before he started trying
to become rich with start-up companies. He said "I once used kinematic design 
to build a lathe to machine plutonium under oil."

I wrote up a description a year or so ago, which I could send to anyone
interested. I don't have a web site yet.
                           Stereo                Stereo
George Gioumousis           /---\        |       /---\ 
                             o o         |       o o  
georggms@xxxxxxxxxx           |          |         |   
(650) 494-6276              \===/        |       \===/ 
                        Photographer          Photographer


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