I'm using a Canon 75-300 III, the non-USM version, that came in a "kit" along with my Rebel T6. I like its reach, but the optical quality isn't great, even if you step it down a bit, and it takes forever to focus.
Then I came across a used 100-300mm lens, a (very) old lens, but maybe optically better/faster to focus than my 75-300.
I have two specific and very related question in this context:
- How would the two lenses compare?
- What could be the issues of buying such an old lens, even considering that the store gave it an 8+ rating, meaning "Used very little, but obviously used. No major marring of the finish or brassing. Optics perfect. Mechanics perfect."