D2X + 17-55DX focusing issue. Help outlining a test? (a little long)

So I think I have uncovered a focusing problem when I mount my nikkor 17-55 DX

lens on my D2X. I don't have a problem with any other lens (70-200, 28-70, 50).

This is what I found.

 

I took some pictures of some kids last weekend at a basketball game. The

portraits were their stereotypical "individual" pictures, kneeling on the

grass, one hand on the basketball kind of shot. Ill post a picture here so you

can see the image I am referring to.

 

Now, the shot looks totally decent at web size, after some nice selective USM,

but it is far from "in focus". If you were to look at the 100% crop, you would

find her face to be VERY unsharp/soft/OOF, but her KNEE is perfectly sharp (the

one sticking up). Even her right hand on the basketball is far more in focus,

which is 4 or 5 inches closer to the camera, and her knee is maybe 8 or 9

inches closer.

 

The camera was set on single servo and Single Area AF, always set on focus

priority. All I did was kneel down, focus lock right square in the middle of

her face, recompose a little bit, and take the shot. I had my sb800 mounted on

my bracket, and it was shot somewhere around 1/200th, f5.6, ttl flash, iso 100,

and somewhere in the middle of the 17-55 range (not sure, don't have exif data

right now). This to me seems like the most basic / surefire way of taking said

portrait. I probably have a hundred thousand shutter releases that I have done

in a similar fashion, with different bodies/lenses, and never had an issue.

 

This same symptom occurs if I am not using a flash, and also occurs when I use

the 17-55 in my garage studio shooting with my Alien Bees monolight. I swap

the lens out with my 50 1.8, and BAM, far far far better results. It doesn't

front focus like this ALL the time, but a very high percentage... id guess

something like 40%?

 

This is happening a lot with this lens. I never encounter this with my 50 1.8,

or 70-200. Is it "front focusing"? I know this is not a technique issue,

because I have been shooting like this with many different leses, on many

different camera bodies, and it appears that it just isn't focusing where it is

supposed to.

 

So my questions are:

 

1) what do you think is going on here?

2) is there a focus test I can perform? Can you outline how it is done?

 

I heard about one using a ruler and a pen? Can anybody provide me with some

nice techniques for actually TESTING for this type of focus issue?<div></div>

You need a test at a similar distance to where you're shooting, but have a look here- http://www.focustestchart.com/chart.html

Thanks conrad, that was a good read, but i don't see how that would work for me shooting from 10 feet...

Forgive me if this is a stupid question...are you absolutely sure you are not set for "closest

object focus"?

Brandon, the simplest test is to find something like a picket fence, brick wall, maybe a

chain link fence, something that has definition where you can see focus points. Find

something big for your ten foot distance. Approach your subect at an angle of 45 degrees

or less. Less is probably better, and this angle would be measured from the plane you'll

be focusing on.

 

Select a point to focus in the center of your frame with the 'wall' extending through the

entire frame left to right. Mark your focus point if you like, shoot the shot at a wide

aperture, I would do it wide open, and see if the focus falls on the mark the camera was

focusing on. In your case you probably want to make several shots and focus to

determine whether there is any consistency or not.

 

If it does focus properly each time, there was a mistake in your portrait session. If the

focus point does not line up, check the consistency, and also check focus manually.

I would also try one

of your other trusted lenses, preferably in a similar focal range. I'm sure you get the idea

here. Somewhere a problem is going to show itself. If the lens is off you will see a

constant inability for the lens to hit the focus mark. This will help you when you send it

back to Nikon, it will tell you if the lens is consistently back or forward focusing.

 

Good Luck, inconsistent problems are the hardest to troubleshoot. It sounds like there is

a problem with the lens. Mine is often soft too, but I can pretty much attribute it to

operator error. At least I've never been concerned enough to think it was the lens.

Obi - yes, I am 100% sure. I was (and always for this type of stuff) using single area AF, using the center AF sensor only.

 

Dennis - thanks, that helps. I am also completely confident that this is an issue with the lens. This weekend im going to break out all my gear and try and get to the bottom of it...