I'm looking for a used 100-400 zoom and wondering if quality/sharpness of lens might vary by date of issue. I see several on Ebay but it's hard to decide which might be worth bidding on. Are there obvious ways to ascertain quality? Any thoughts would sure be appreciated. I know there is a code that will lead me to a manufacture date but I don't know if that is helpful information. Thanks.
Buying used has it's risks especially when you can't test shoot before buying. Do you have local Buy & Sell sites like Kijiji? As for dates yes they have a date code and obviously really old lenses likely saw a lot more use than ones which are a year or 2 old but there are always exceptions. Ask for full file samples shot wide open at different focal lengths. Verify they came from the lens using the EXIF. Ask for a few shot at lower shutter speeds to see if the IS is working. Ask how smoothly the push / pull zoom mechanism is or better yet test it by shopping locally. Real early models seem to have been less than perfect but mine (bought used) is from 05 or 06 & is very sharp & still zooms smoothly.
Thanks so much for your thoughtful answer to my post. I am new to this forum and really appreciate the knowledge that is available here. I think you are convincing me to just step up and buy new. My community is too small to buy used locally, and the online options seem filled with lots of variables that may make a used lens no bargin.
Depending on where you live right now it may be a big stretch suggesting spring isn't far away & Canon often has rebates on many lenses each spring & that one may be one of them. B & H or Adorama may also be good places to watch for a sale price.
As a lens is heavily used, things inside can start to loosen up. But this means the performance will vary on usage and not by date (I can have an older lens that was lightly used not perform nearly as well as a newer lens that was heavily used.)
Sometimes when people are selling used lenses it's because they find they just aren't using them nearly as much as they thought they would -- these are lightly used lenses. Other times it's because they're no longer happy with the lens (which could be an indication of things loosening up and the lens needing service.) There's no way to "know" what you're getting without actually evaluating the lens (and knowing what to look for.)
One nice thing about "L" series lenses is, they can be repaired. Which may make a certain lens a bad buy but not a total wash out.
Hands on is the safest way but, where I live there are no camera sources close by. This severely limits my selection and availability. Possibly yours too?