I am fairly certain they are the same but just wanted confirmation. I've owned the M-mount one for a few years now and love it for portraits and such. Slow, yes, but a great signature and I got it so cheaply. After acquiring and really enjoying using a IIIa last year I decided to watch for a LTM version. Found the one on the left recently, again for a very nice price and having been CLA'd by Sherry decided to grab it. Just shot the first roll on some Eastman XX and so far looks great. Being such different looking lenses and made so far apart I just wanted to confirm some of what I've read online: other than a 3-element version made for a very short time, all 90/4 Elmars, LTM or M-mount, are identical in formula? Comment?