How long will a lens last?

What is the average life span of a lens? If you wanted to buy a used lens ( an L lens) how old of a lens would you feel comfortable buying? Assuming it was used on a regular basis.

If it's properly taken care of, the life span should really be indefinite. Of course, the technology has changed a good bit in the last 5-10 years as far as coatings and such go.

I have manual focus N*kon lenes that my dad bough used back in the 60's and they still work flawlessly. However with modern AF lenses I would be hesitent to buy anything more than 1 generation out of date, as service will be nearly impossible if it breaks. So for instance I would buy a 400 2.8IS, or a 400 2.8 mk2, but not the mk1 as not only does Canon not service them, but getting a part from a 3rd party lens repair shop will be next to impossible.

I have a couple of Canon lenses from the 1960's that are still functioning well.

I use some older lenses (see my signature), but I wouldnt like to speculate on how long a modern autofocus would last, after all the old lenses were manual focus, the modern ones have motors to go wrong, the IS ones have even more gizmos to go wrong.

I do have one faulty older lens, I have two Pentacon 50mm F1.8 primes & one has its iris stuck wide open, but to be fair I do remember my brother dropping it on a stadium at "Silverstone" raceway over 15 years ago, that could have something to do with it!

Nick

The only major innovation in the last 5-10 years is IS and maybe some coatings?