24-70 L Focus Issues

Picked this lens up used from a fellow POTN member, and was told it was 100%, after this past weekend shoot i noticed that most shots were soft/OOF
So I got a lens focus test chart and took a few shots,
Both are shot at F2.8, first shot is manual focus on black bar in middle, second is auto focused on black bar.
Both shots were taken on a tripod and with a 2 second delay to ensure no camera shake.
http://kevinblackphoto​graphy.files.wordpress​.com/2010/04/img_1494.​jpg

http://kevinblackphoto​graphy.files.wordpress​.com/2010/04/img_1495.​jpg

From the pictures it looks like sevre backfocus issues.
Any idea what to do now? Is it time to send to canon to get fixed? If so does anyone know the average cost to get this lens looked at?
Thanks
Kevin

I think its $158 to even look at it (although they replaced my AF mechanism as part of that cost)

Its quite possible the lens IS 100%.. just not on your camera. My 24-70L requires a little micro focus adjustment on my 7D.. come to think of it, all of my Canon lenses require MFA.. but none of my Tamron or my Tokina require MFA..

This morning I was just thinking about selling my 40D to get into a 50D just for the MFA alone.

The lens is fine most likely, it is just your body is not playing nice. Read here:
http://www.lensrentals​.com …s-is-soft-and-other-myths

Couple things, First, it' doesn't look severe, just a tad off. In the first pic it looks almost spot on. The second does show a little back focus but I wouldn't call it severe. It looks as if your alignment is not quite right. Your tilted a bit. When shooting a focus chart make sure your perfectly aligned. Also, both these are at 24mm. Is it also off at 70? Lastly, as mentioned every lend and every body are a little different. A lens can be back focusing on one body and front focusing on another. You may have to send the lens or body in to get it calibrated.

the first pic was manually focused so i guess it senses it a little better then? I just figured out why it was tilted, the oen tripod legs was sticking out slightly...very stupid mistake, I will see if i can borrow another body or two and test it out. thanks for the help guys

You aren't supposed to manually focus for these tests.

Rack your lens fully OOF and let your rig focus where IT wants to focus.
Also, do it several times and examine the images for a pattern of misses. This should be pretty obvious over the course of say, eight or ten frames.

One and Done tells you nothing.

FlyingPhotog wrote in post #9941139
You aren't supposed to manually focus for these tests.

Rack your lens fully OOF and let your rig focus where IT wants to focus.
Also, do it several times and examine the images for a pattern of misses. This should be pretty obvious over the course of say, eight or ten frames.

One and Done tells you nothing.

+1

And if you have a UV filter installed I'd take it off for the focus test just to be sure.

FlyingPhotog wrote in post #9941139
You aren't supposed to manually focus for these tests....

I think it was manually focused to see what optimal focus would be. THan auto focused to compare to the manually focused pic.

So, went out and bought a 7d, found at 24mm focus was best at -14 micro adjust... at 35 ish it was almost bang on without adjustment, and at 70mm it was best around -4 ... So it looks like its time to send in the lens

rideuntildeath wrote in post #10010690
So, went out and bought a 7d, found at 24mm focus was best at -14 micro adjust... at 35 ish it was almost bang on without adjustment, and at 70mm it was best around -4 ... So it looks like its time to send in the lens

I asked a Canon Rep about calibrating zooms and he told me the "official" Canon line is to check both ends and average the two.

this lens is a known lemon. i had to send mine back to canon 5 times before they even acknowledged it stank.

Did you shoot in "AI Servo" mode ?

Notice that in that case, my 5Dii is always missing the focus !

The test images need to be square to the camera or it will tell you nothing. From a quick glance it all looks fine, but the left side of both tests tells a different story to the right side. You need to take the tests again.

I notice with all my lenses, the actual focus point is never in the same place twice, add in the fact that it will focus differently at different focal lengths and it becomes an excercise in averaging all the different "errors"

bluefox9er wrote in post #10011251
this lens is a known lemon. i had to send mine back to canon 5 times before they even acknowledged it stank.

Rubbish. The lens YOU had was a lemon. That does not mean all other copies of the 24-70 are lemons.

Trixster! wrote in post #10011366
Rubbish. The lens YOU had was a lemon. That does not mean all other copies of the 24-70 are lemons.

no, not every lens is a lemon, but there are known serious quality issues with this lens that canon have even acknowledged.

and just because *yours* is fine, it dosn't mean every single one manufactured is *fine*.

it's like playing russian roulette..just because *your* brains don't get blown out , it dosn't mean it's a safe thing to do.