Elmar-M 50mm with slight back focussing

Hi all
I picked up a Elmar-M 50mm f3.5 and the seller said that it had "slight back focusing issue" is that possible? Has anyone heard of that with this lens? What's the best method of testing?
I can't see that anyone has ever worked on the lens and the lens it self looks in beautiful condition with only a slight bit of wear on the mounts.
It has a very slight bit of the usual Elmar fog, which I probably won't worry about.
Puzzled cause it was really cheap, not sure if the guy had it correctly locked in when he used it. There is no play once locked in. It even come in a brand new Elmarit f2.8 28mm box and sheath.

This is a nice Elmar lens, in the newer body that accepts 39mm filters. I don't understand the back focusing. I wonder how the seller detected or measured it? And did he base it on one M body only? Two suggestions:

1. Take pictures with a fine grain film.
2. Definitely have the fog cleaned. YYE told me during a long phone conversation that the aperture is too close behind the front element in the 2.8 Elmar. Your 3.5 has the same body. Some chemical causes fog and etching. So do clean it.

Make sure the rear element is fully seated? That's the only guess I have for focusing issues. I have a lens (ltm elmar) where the rear element was partly unscrewed for some reason.

Kodachromeguy said:

This is a nice Elmar lens, in the newer body that accepts 39mm filters. I don't understand the back focusing. I wonder how the seller detected or measured it? And did he base it on one M body only? Two suggestions:

1. Take pictures with a fine grain film.
2. Definitely have the fog cleaned. YYE told me during a long phone conversation that the aperture is too close behind the front element in the 2.8 Elmar. Your 3.5 has the same body. Some chemical causes fog and etching. So do clean it.

Click to expand...

Thanks, I'm thinking it is just user error, who knows if the camera was out.
It was so cheap was willing to take the risk it had a problem. I have two red LTMs I have disassembled to clean before, the M version looks a little more difficult, maybe. I'll find how much they're charging.
I like the Elmar @ f5.6/f8, very sharp and nice contrast. The M version is much better to change f stops.

Don_ih said:

Make sure the rear element is fully seated? That's the only guess I have for focusing issues. I have a lens (ltm elmar) where the rear element was partly unscrewed for some reason.

Click to expand...

That's one possibility I thought, but it is all good and can't see any marks on the element flanges, so doubt if it has ever been touched since leaving the factory.
Will try and test it out next week end and see for myself before I do anything else.
I picked up a M3 DS recently and the Elmar will be a great match.