03-10-2015 10:15 PM - edited 03-10-2015 10:17 PM
On all lenses or on just one lens? Was it working all right and then went bad, or was it always bad? If you're not a beginner, you know you haven't given us enough information to go on.
03-11-2015 08:12 AM
I use a 50 1.8 and 50 1.4 and its worse on my 1.4
It's not surprising that it's worse on the 1.4 than on the 1.8, but the fact that it happens at all is obviously a cause for concern. Does it consistently front-focus or consistently back-focus? If so, the camera's AF mechanism may be out of adjustment. Unfortunately, the T3i doesn't have AF microadjustment, so trying that isn't an option. Before you send it in, though, it might be helpful to see how those lenses behave on a different body.
03-11-2015 08:44 AM
03-12-2015 08:07 PM
03-13-2015 10:55 AM
"Yes it does front and back focus often can't tell ..."
The lens can't do both. If it is truly missing both front and back, it isn't fornt or back focusing. It is simply OOF.
The easiest thing to do is, like Bob from Boston says, try it on a different camera. Also try another, her lens, on your camera.
At this point, you must find out which is at fault. Then decide your course of action.
If it is the 50mm f1.8, it is a throw away. If it is the 50mm f1.4 you can check on service cost as it may be a toss up. If it is the T3i you will need to get an estimate, as it too may be time to upgrade.
If it is "you", you need to change your shooting habits!