Need some opinions.

[tomhooper]

Here are a couple of shots with my old (12 years or more) Tamron 200-400 mm zoom. I can't seem to get the focus sharp and am beginning to think its the lens. I am also on occasion seeing a blue halo or chromatic aberration on the edge. Would welcome all thoughts. Thanks.

[gaea106]

My first thought would be take it and clean it really good, but I always go for simple answers first.

[DigitalScape]

I can't tell if the lens is back or front focusing, or if the focus issue is due to camera motion - were these shot with a tripod? 1/125 second may not be fast enough for you to handhold at ~400mm - nothing appears to be in focus on the two sample shots. To me, it looks like both shots are over exposed which may be contributing to the blue halo or chromatic aberration on the edges.

[venchka]

Originally Posted by gaea106

My first thought would be take it and clean it really good, but I always go for simple answers first.

That and set up a controlled enviornment. Camera on a tripod. Several exposures at different focal lengths & focusing distances. By that I mean exposures near the minimum distance going thorough several focal lenghts. Then back up and repeat. Finish at or near infinty. Try manual focusing as well. Also, taking pictures of a large tape measure at about a 45 degree angle and keeping track of where you focus on the tape will tell you if the lens+camera are focusing correctly.

[tomhooper]

I did a series of test shots. It does get soft at higher zooms. The CA also gets worse at higher mag. These two shots were with a tripod and the second was with mirror lock-up and remote shutter release. Don't remember about the first. Both AF and MF come out about the same. I did a little research and found a couple of articles that stated that this lens had focus and CA problems at high zoom. Oh well. Now I can tell my wife I need "L" glass. I always make lemonade.

[tomhooper]

Oh and I had cleaned the lens thoroughly only a few days before the 2nd shot.