In relation to the posts above, some images of devices with significantly altered stereopsis compared to regular Porro prism binoculars:
a) When Zeiss commenced production of Porro prism binoculars in 1894, they also offered a handheld Stereo Telescope, aka a Relief-Fernrohr
(it uses a variation of the Porro Type II prism, with one of the four right angle prisms located at the front of the objective) *
b) While the above never saw much civilian use, by 1904 it had been enlarged and was used in mounted form for military use.
See an image from a catalogue by Cassidian Optronics (the catalogue from 2012 is titled Handheld Targeting Systems,
and on the front page it indicates 'Optics by Carl Zeiss').
c) Enhanced stereopsis was essential to the operation of coincident image rangefinders (aka telemeters).
Depending on the task they went all the way from handheld sizes, as shown in the Cassidian image; to as Bill indicates those for shipboard use.
See an image from 1912 at:
USS Nebraska Naval Ship Cover 1912 From Ship Post Master Range Finder RPPC | Topics - Transportation - Boats, Postcard
d) And the Pentax Papilio reverse Porro prism binocular uses significantly altered stereopsis in a different way.
To achieve a minimum focus of only 50 cm/ 20 in, the objective lenses in each barrel move closer together.
See the images in post #4 at:
Where are the aspherics?
And finally, there were not only stereo enhancements to vision! See an image from:
https://mobile.twitter.com/beidaihebirder
John
* In the early 20th century Zeiss also offered other hand held binoculars with exaggerated stereopsis.
See post #91 at:
New Horizons II