rangefinders

[T3D Peter Abrahams <telscope@xxxxxxxxxx>]

There are lots of coincidence rangefinders for hunters, etc., but I haven't
seen a consumer model stereoscopic rangefinder.  They would be harder to
use, no more accurate, but visually more rewarding.  I'm lucky to own a WWII
'battery commander's rangefinder', which is a binocular with objectives 18
inches apart.  The views are spectacular.  They turn up a military
collector's shows.  Zeiss tried marketing them as consumer items when they
introduced the first successful prism binocular in 1894, but they never
caught on, except for military use, where they are faster in use, for
sighting shell bursts, etc.
>binoculars  with reticles ... sort of fenceposts 
>meandering zig-zag across the field of view.  The fenceposts were at different 
>distances and had ranges tagged to them.  You set one of those fenceposts 
>on top of your object and you've got the range
Unless these had a mechanism for shifting the image of the reticle across
the field of view, they were a variation of the common reticle, that allows
you to estimate the distance to an object of known size.  I have not seen a
moving reticle in a  binocular, and would track down the model if given any
details, it would be very unusual.

The next issue of Amateur Telescope Making Journal will have my 1500 word
article on Rangefinders and Stereoscopic Telescopes.  About 1/2 of it was
posted to photo3d during the quiet hours when the big yakkers were partying
in Rochester, so it is in the archives.  On request, I will post it all to
tech3d.  On request, I will not post it to tech3d.  I'll also e-mail it to
anyone.  Pending your response,  I will post from my notes on the subject.  
Jim Rose was the civilian supervisor of the Long Beach Naval Shipyard, now
retired to Portland OR.  He was an instructor for rangefinder repairmen, and
his recollections are extensive.
The big battleship rangefinders were built around a particular gun, and
there were many types, both coincidence & stereo.  The biggest was the Mk.
52, 46 feet long, stereoscopic, 25 power, about $100,000 in WWII, about
10,000 lbs., near focus 5000 yards.  There was also a Mk. 51, 46 foot,
coincidence, monocular viewing.  There were 15 foot models mounted in
gimbals, servo connected to a gyroscope, to keep the horizon level. My notes
read:
"The user sees enhanced stereo through stereoscopic rangefinders, not two
images, have to be able to see stereo to use rangefinder.  In one system:
superimposed on the stereo image were 'wander marks'-a reticle with series
of outlined diamonds, appeared to float in air, diamonds moved, when object
seemed to be same distance as diamond, range set.  Entire pattern is in both
reticles, they don't move & are fixed, but movement of optical wedges make
it appear to move.  Reticle is in erector system, diamonds engraved onto one
surface, reticle at focal point of objective, no calibrations (numerals)."
There were a variety of hand held stereo rangefinders, in both world wars,
used by all parties, these days you see  Japanese, German, and US made
models, apertures 30 to 50mm, distance between objectives varied.  More
common are what the Germans called "Scherenfernrohr", scissor telescopes,
that fold at a hinge near the ocular into a twin periscope (trench
binocular).  "Stangenfernrohr" or pole telescopes have the objectives on
either end of a rigid tube, usually 3 feet long.  All of these devices are
very difficult to clean or collimate.
Stereo rangefinders are wonderful devices, incredible to use, much R & D on
them between WWI & WWII.  I could go on at length, but will wait to see
about posting an article.
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  Peter Abrahams    telscope@xxxxxxxxxx
the history of the telescope, the microscope,
   and the prism binocular


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