more info on this interesting & rare lens:
Mike's Camera Database
"Following the fashion of the time, Petri created a secondary brand name for its lenses. Pentax had its Takumars, Minolta had its Rokkors…and Petri had its Orikkors. The non-standard-focal-length M42 Orikkors were supplied by Kyoei, itself a small and obscure manufacturer. But the standard Orikkor 50mm f2 - despite a few Petri-dictated design cues shared with the Kyoei-made lenses - seems to have been furnished by some other company. It's often possible to make informed guesses, based on styling idiosyncrasies or commonalities, about the real manufacturer of an "anonymous" Japanese lens; but I must confess that I have no idea who was responsible for this Orikkor.
It's a small lens, but weighty in the hand, and nicely made and finished - a preset, with ten aperture blades. But to my mind, its single most interesting feature is the 7-element/4-group optical layout. (Remember that at this time (1959), most other SLR brands were content to offer 6-element standard lenses of conventional double-gauss design, especially in the case of their moderate-aperture models - f2 or thereabouts.)
But the story doesn't end there. The Orikkor is not, as you might suspect, an SLR variant of the 7/4 f2 lenses offered for the rangefinder cameras of the day: the Leitz Summitar/Summicron, the Chiyoko (Minolta) Super-Rokkor and others. Instead, the Orikkor incorporates a cemented triplet in its rear group. There may be other standard SLR lenses that adopted that scheme, but I can think of only one offhand: the somewhat uncommon 8-element 50/1.4 Super-Takumar of 1964, whose cemented triplet is said to have been so expensive to manufacture that Asahi lost money on each and every lens it sold. That puts the Orikkor in very distinguished company indeed."
Post #33 by skolkmeier
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