I have just bought a Vivitar 100mm f/2.8 Macro Lens [advertised also as LESTER DINE KIRON 105] Olympus OM mount, and yes it begins with the "22" serial number [as advised by Ned]. I scoured the threads dealing with this lens and became convinced it was the best legacy Macro in the longer range. I already have the P/L 45, with which I am most happy. Recently I bought an Olympus 4/3 digital 35mm macro, which actually works [AF etc] with the Kenko tubes [10+16mm] stacked [which the PL45 does not with the first iteration of the Kenko tubes]. However, the resultant close working distance is too close for live, active spiders. So I will sell it when the V 100 f2.8 arrives in about a week. I am hoping that a 3X Vivitar tele-extender in OM mount, which I scored on impulse a while back, will give me a killer beyond-macro combination, when combined with the Vivitar 100mm f/2.8. I will even try adding the tubes to see if I can get even greater macro. Yes, I know tele-extenders do degrade optical performance but it was an under $20 bargain. Has anybody else tried adding extenders or tubes to the Vivitar 100mm f/2.8 or similar macro lenses on m4/3? I love getting right up close [visually] to my spiders.