Canon Community

I have a relatively new 70D and used it with brand new Tamron 16-300 lens.  Had trouble with autofocus under easy conditions.  Was provided another lens and had less trouble.  Then used with old Canon 70-200 2.8 IS and now notice same issue.  Times t...

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 wo...