Action Sports Cartel

Hey,

I think it was back in the WaW days that someone helped me out with this, but my problem has arisen again.

My EF 17-40mm f4L is back focusing big time. I noticed it earlier this month shooting the BC Games, I was shooting podium pics and I could see through the viewfinder that the photos were out of focus. More recently, I was shooting some casual family photos for my girlfriend's family and noticed later on that the back wall was tack sharp while their faces were soft.

I've tried twisting the focus ring back and forth trying to "work it out", as someone requested to me once. Anyone else have any tips or tricks to help with back focusing? I know it's only this lens, as my 50mm f1.8 and 70-200mm f4L are tack sharp all the time. I'm shooting with a 20d.

sounds odd that it focused right before.

in the viewfinder when the focus beeps. it looks Out of focus? have you turned the diopter adjuster on the viewfinder?


other than that, there's not much you can do against focus problems
i have used a bunch of L lenses from 14mm to 400mm and i've had a bit of front/rear focus with most of them, in fact. the lens with the most accurate focus that i have is a 35 2.0 for 200bucks


talk with your canon rep for a price estimate, i'm going to send my stuff in when the season is over. canon professional is a joke and they say that focus errors isn't their fault so they won't keep their 48hour service... they want to keep my stuff for about three weeks

Yeah, diopter is at 0, it looks out of focus in the viewfinder and the resulting photo is out of focus. I tested it last night and also noticed that my original problem is back: focus shifting when I zoom out. Before I had back focus issues I would zoom in, focus, and then pull out and the scene would go out of focus.

I tested this yesterday with an old canadian tire receipt. I zoomed in and focused on the center of the receipt. The viewfinder and the resulting photo showed good focus. Zoomed out to 17mm and my point of focus moved about 10 cm closer than it was before.

Sucks big time, time to send it away for calibration.

Steve Simons wrote:
Yeah, diopter is at 0, it looks out of focus in the viewfinder and the resulting photo is out of focus. I tested it last night and also noticed that my original problem is back: focus shifting when I zoom out. Before I had back focus issues I would zoom in, focus, and then pull out and the scene would go out of focus.

I tested this yesterday with an old canadian tire receipt. I zoomed in and focused on the center of the receipt. The viewfinder and the resulting photo showed good focus. Zoomed out to 17mm and my point of focus moved about 10 cm closer than it was before.

Sucks big time, time to send it away for calibration.

did you test just focusing it at 17mm? A lot of lenses shift their focus as you zoom through the range, so the zoom in to focus thing is no good...

The focus didn't shift when I bought it. It was fine for about a year and then I had it in my camera bag for the winter and the next time I used it something didn't seem right. However, it went back to normal another year later. It's weird, I know, but a friend who borrowed it had the same problem.