I a post below ("vivitar and tokina lenses for OM"), Eric Friedemann wrote: "... back in the day, Tokina made several lenses for Olympus, including the 35-105mm OM zoom." I have read this several times on the internet (interestingly never in any printed documentation), and the Tokina/Zuiko lenses look indeed very similar. The difference in marking as "3.5-4.3" (Tokina) vs. "3.5-4.5" (Zuiko) is probably meanigless. If I remember right, however, the "close focus" ring on the Tokina is turned in the opposite direction than that of the Zuiko lens. I cannot rationalize why this (relatively major, mechanical extra) effort to distinguish these lenses would have been made. Is there any sort of a (half) official or otherwise "authorative" document which supports Eric F.'s argument? Has the Tokina RMC also changed its optical design in 1985? As for the Zuiko lens, there is an "exploded view parts diagram" available (marked as "Olympus" with all part numbers in the standard Olympus nomenclature: mostly two letters followed by 6 digits; also screws common with other lenses have common part numbers); it would be nice to see a similar diagram for the Tokina lens. What are the other "several" Zuiko lenses made by Tokina? The Zuiko 40/2? Both lenses have on the back a 4-digit white code which reads "NIxx" where I assume that the first two letters indicate the manufacturing plant. To my knowledge, no other Zuiko lens has an NIxx code. Interestingly, both lenses have the same production period (early 1983 to mid 1986). So it could be that for this period, Olympus had some _very_ close collaboration with Tokina. It is then also the question: who has designed the lenses, Tokina or Olympus? The 40/2 "pancake" was announced (with a picture) as a "50/2" from Olympus as early as 1976 ("6 elements in 5 groups, min. aperture f/16, min. focus distance 65 cm, 140g, 21mm long 59mm diameter, 49mm filter size"; note the differences to the final 40/2), and this original idea never materialized. Might it be that Olympus has given up on it and led Tokina finish the job? Is Tokina to blame for the mediocre performance of the 40/2? Some people also argue that the late Zuiko 50-250/5 would have been produced by Tokina, probably mainly due to the somewhat similar Tokina AT-X 50-250/4-5.6 lens. In this case, however, I do think that the Zuiko "TNxx" code on the back indicates that this lens was manufactured in the Olympus Tatsuno plant.