I own a 450D and recently got myself a walk around 18-135mm EFS lens to play with.
I've been having problems recently with focusing, especially in indoor areas and rooms with half the lights turned on. When I hit the focus button, the camera gets a lock and the red dots on the focusing plate light up.
Thing is when I take the photo and blow it up 100% on the computer, they are very often out of focus.
I don't have this problem much outdoors and I'm beginning to think that DSLRs use several methods when it comes to focusing.
Correct me if I'm wrong, but do DSLRs use infrared light to help focus in darker areas? If so, how do I know if my infrared light is spoilt?
If not, are there other reasons as to why my focusing is off? I had my focusing plate changed about a month ago, I'm not sure what else might be causing this problem. I hate to think it's the 18-135mm lens that's causing the bad focusing since it's new.
Below is an attached image I took, the person in front is suppose to be the main focus but as you can see he's not as sharp as I'd like. Bumping the iso up to 1600 wasn't some thing I like to do, but I thought it might help increase the shutter, the picture is still blur, I seldom get this problem until this month only, after using the camera for over a year.