coincidence periscope

[T3D Peter Abrahams <telscope@xxxxxxxxxx>]

While going through my notes for my earlier post, I found 'coincidence
rangefinder periscope'.  Not knowing what I had heard, I asked my opticalman
friend what he had meant.  It turns out that there was such a thing, with
objectives vertically oriented.  Periscopes were up to 30 feet long, so
there was room for a rangefinder.  This would have been US Navy, mid 20th
century.  
Vertical rangefinders are quite new to me, but I can imagine that sighting a
ship, an island, (or the horizon, if such a thing is possible at that low
viewing angle), would be much easier with coinciding images, if they moved
in the viewfinder across their long axis, not along it like they do in a
normal coincidence rangefinder.
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  Peter Abrahams    telscope@xxxxxxxxxx
the history of the telescope, the microscope,
   and the prism binocular


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