Have I got a bad lens? How would I know?

[sdotkling]

Just bought a very pretty, slightly wobbly Canon 50/1.8, and immediately sent it off for a repair and CLA. Now I've just scanned the first few rolls I shot with it since I got it the lens back, and I'm appalled at how clumsy my focusing apparently is. Or is it the lens?

Here a couple of samples. In the first, the focus seems to be on the wall 2 feet behind the woman...but I surely would have focused on her face.

Same thing in the second. The focus seems to be on the door behind the kid. (This being a quick grab shot, I might have indeed been focused elsewhere, but I vaguely remember thinking I nailed it.)

Shooting with my Canon 35/2, I am apparently as graceful as a gazelle. Focus doesn't seem to be a problem.

Anybody got a clue?

 

[Sonnar Brian]

Either your camera's RF is off, or the shim on the lens is off. For the latter, back-focus is caused by the shim being too thin. I would send the lens back to the place that CLA'd it and have it corrected.

 

[Daan]

but first do a couple of easy test shots. I often blamed a lens, but it's usually me.

 

[sdotkling]

Crude test completed. I measured out the driveway, and put numbers on my minivan at 1-foot increments. I focused the rangefinder of my M2 on the "X" and moved it every shot. Clearly, the focus falls 2 feet behind the point I think the camera is focused on. Back it goes to the repair guy.

Pardon the incredibly crude test. Science isn't pretty.

 

[Frontman]

I use ground glass and a 10x loup, along with a measuring tape. I simply check at 1 meter and infinity, making sure the image in the ground glass is clear when the lens is focused at objects at those distances.

Shimming the old Canon lenses is not difficult, I'm surprised your repair guy didn't do it correctly.