Wondering about invention of microprisms screen

[Europan]

Hello, all. My research on the coming of microprisms gets lost in the dust, I can’t seem to find the originator/s different to the inventor of the split-image device who is clearly Lucien Dodin. My starting point is the 1963 Double-Eight film camera Agfa Movex Reflex which is the only one in that format with a microprism array in the finder.

I know that Asahi presented the first SLR camera Pentax with a microprisms focusing aid in 1957. Does anybody have a little more information or a hint where to look further around? This subject has all the ingredients of a thriller with a lot of suspense, I am inclined to say, you don’t know how long you’re lost.

 

[Bikerider]

My first Pentax, a SV which I bought in 1965 certainly had a microprism and I don't think it has been bettered. Other manufacturers have used them, but they didn't have the crispness of Pentax. However when they were first used with a camera body, I have no idea, but I feel certain they were known about for quite sometime before they were first used as camera focussing aids.

 

[Europan]

Thank you for the contribution

 

[reddesert]

Searching patents will likely help a lot. I'm using US patents here because they are easy to search (and for me to read); some of these were patented a few years earlier outside the US.

US Patent 3195432 to J-M Baluteau of SOMHP (France) seems clearly relevant, showing what a reflex viewing system with what looks like a microprism screen: https://patents.google.com/patent/US3195432A/en (1965, original French patent 1959).
They cite a previous patent US 2969706 to Rosier and Baluteau https://patents.google.com/patent/US2969706A/en which doesn't seem to use microprisms, but it does cite an article by Dodin, "Focusing with Crossed Prisms" in Amateur Photographer.
There is also cited the earlier US Patent 2986599 to Lindner and Kosche https://patents.google.com/patent/US2986599A/en showing a microprism screen in an electronic (TV) viewfinder. This patent cites Dodin https://patents.google.com/patent/US2669916A/en , which is clearly a patent for a split image rangefinder (but not microprism). Lindner and Kosche refer to their own article "A New Optical Rangefinder for Television Cameras," in Nachrichtentechnik 1956, No. 12, pp 538-544, so now you just need to find some back issues of Nachrichtentechnik (literally "News Technology," but as I'm sure you know better translated as telecomms engineering).

I got to the Baluteau patent by tracing patents referred to and cited by through several patents including:
https://patents.google.com/patent/US2589014 to McLeod of Kodak, which is clearly earlier but describes a sort of screen made up of cones, not wedge prisms.
https://patents.google.com/patent/US3003387 a Rollei patent for a screen that combines Fresnel and focusing surface onto a single surface.
https://patents.google.com/patent/US4352547 a much later 1981 Nikon patent for a method for optimizing the microprism wedge angles.

 

[AgX]

We should differ between patent application and manufactured devices. The latter could only begin when economical manufacture became possible, technologywise.

 

[wiltw]

We should differ between patent application and manufactured devices. The latter could only begin when economical manufacture became possible.

Indeed true! Pentax showed the first camera with TTL metering at a trade show, but Topcon beat them to the market with their RE Super (a.k.a. Beseler Topcon Super D)