Lens calibration

For a while now I have felt that one of my lenses (28-70L) was a little soft with regards to focus. Not that the images I was getting were really out of focus but just that when I zoomed in at 100% in Photoshop they didn't seem to be as tack sharp as the images created by my other lenses. As I am going away on vacation this week (tomorrow) and this will probably be my most used lens I wanted to be sure everything was spot on with regards to this issue.

My first test was done a couple of weeks ago when I shot some photos of my better half, hand holding the camera and focusing on her eyes. The results showed the focus to be bang on with no issues. Still not convinced I searched online for a calibration test as my camera (Canon 5D Mark II) allows me to calibrate individual lenses to the body.

I downloaded the scale above (it can just as easily be created on any sheet of paper), and set the camera up for the test as per the image below.

The camera was set up on a tripod and fired with a remote control to eliminate the possibility on any camera shake caused by me hand holding. I zoomed in the lens as far as possible and opened up the aperture all the way to F2.8 to have the smallest depth of field, adjusted the shutter speed to get the proper exposure, set the autofocus to focus on the line in the middle of the scale and took 5 shots for comparison. Each of the images were identical in focus (as they should be). See the sample image below.

While there was a slight difference in the front and back focus the test showed me that this was minimal (and acceptable) and the lens didn't need any calibration. As this lens has no image stabilization (IS) I will make sure I never shoot slower than 1/100 second and will make sure my focus point is set exactly where I want the image focus to be. This is even more critical as I tend to shoot quite a bit in the F2.8 - F4.0 range.

I believe this is a great test that everyone should try once in a while with all their lenses even if your camera doesn't allow for any calibration. Even if it does or if you find something off and don't feel comfortable doing the adjustment yourself take it in to a camera shop and let them do it for you.

To sum it up I feel any "softness" I saw before in any of my images was the result of the operator (me) and more care will now be taken when using this lens to ensure tack sharp images.