24-70 Focus Test - how close to MF should AF be?

I am hoping someone could lend some advise. I have been unsatisifed with recent results from my 24-70/2.8 & 40D combo, as I have seen softness I never had with my 30D.

So out came the focus chart today and here are the results.

The top line is auto focus, the bottom is manual focus. I am seeing manual focus distinctly sharper than auto. Is this within spec? The difference doesnt seem so bad and I'm leaning toward user error here.

Auto Focus

Interesting, I'd like to know as well. My 24-70 comes in 2 days and I've read 3 different focus/soft problems with this lens. :X

Ideally, they should look the same. But AF can mess up, as can MF, and that doesn't automatically mean the camera or lens is at fault.

What metering mode are you using btw? Are they both center-focused on this sentence?

I think it sucks.
You're thinking the problem is with your 40D body, right?

vincewchan wrote in post #4392306
What metering mode are you using btw? Are they both center-focused on this sentence?

Metering mode: Evaluative

They are both center focused on the 'focus here' part of the focus chart. Click to see the larger version to see that.

xarqi wrote in post #4392388
I think it sucks.
You're thinking the problem is with your 40D body, right?

I am not really sure about this. I am going to check now with the 50/1.4 and compare. I am leaning on it being the 24-70, to be honest.

My main issue is am I being too much of a pixel peeper here? My real world results arent great, which is why Im doing this.

maxxed wrote in post #4392486
I am not really sure about this. I am going to check now with the 50/1.4 and compare. I am leaning on it being the 24-70, to be honest.

My main issue is am I being too much of a pixel peeper here? My real world results arent great, which is why Im doing this.

You are doing it right, in my opinion. Having found an issue in the real world, you are pursuing it with the appropriate tests. The reason I'm fingering the 40D is that you didn't have the same issues with the 30D. Still have that for a side-by-side test with the 24-70?

Unfortunately I dont have the 30D anymore. I'll stick the 50mm on there in a few moments...

Something doesn't seem right here. If you look at the enlarged versions of the charts it would appear judging from the dof that the optimum focus point is exactly the same for both the manual and the auto focused shots. If the auto focus was 'off' slightly at the ' focus here' spot then surely some other part of the chart would be in sharp focus manifesting itself as either a front or rear focus problem. This suggests that the probelm is camera shake on the auto focused shot - or am I missing something?

In both cases the camera is tripod mounted and shutter was fired via the timer.

Here is the same test with a 50mm 1.4 at 1.4. The result is very similar, AF or MF, which seems to indicate the 24-70 needs a focus adjustment

Auto Focus

I'm not so sure about that. I think your body is front focusing by about 2mm. You can see it with both the 24-70 and the 50.

That said, I'd counsel against relying on just one or a couple of tests. Do it a few times, setting up from scratch each time, just to be sure it's real and not some quirk of alignment or technical variable in a particular test.

Maybe you could try again with the 50 at say f/2. I know DoF would increase, masking focus errors more, but the image is pretty soft in the test you posted. Even at f/2, if it's a focus problem, it should still show (hopefully).

ok ill set up for another try

Any new results?

Are you using a tripod? Are you selecting the same spot of focus?