Focus with the 24-70 and the 50D

[private]

I think something might be wrong with my lens or camera - not sure which. I had the focus set on his face (his eyes to be exact) but when you look at the pic - the focus fell on his clothes instead. What can I do to figure out what is going on with my camera/lens...

[RichardTaylor]

Some thoughts
Were you using autofocus?
If so what focus point did you select or were you using automatic focus point select?
Or did you focus manually & recompose and the subject or yourself moved slightly in the Z plane?

Did you have a filter on the lens that may have caused problems with focussing?
Have you tried this camera lens combination on a static flat subject like newspaper to if it will focus ok on that?

Was the same camera/lens used on the same recent portraits in your flickr stream?
They appear to be ok.

[Samanax]

The lens may be front focusing.

The 50D has the micro adjustment feature. You might want to see if it helps.

[private]

Originally Posted by RichardTaylor

Some thoughts
Were you using autofocus?
If so what focus point did you select or were you using automatic focus point select?
Or did you focus manually & recompose and the subject or yourself moved slightly in the Z plane?

Did you have a filter on the lens that may have caused problems with focussing?
Have you tried this camera lens combination on a static flat subject like newspaper to if it will focus ok on that?

Yes to Auto focus, used the central focal point in manual mode. No filter (forgot the hood tho') and I will try on something that does not move

[CaptainNH]

Was this a one-off problem or is it now repeating itself? Just this lens or is it affecting others?

If it's a one-off, it's probable that one of you moved backwards a touch and you shouldn't worry about it.

If it's repeatedly front focussing, as Sanamax suggested, you can fix this up with a micro-adjustment either for this lens alone, or a global adjustment for all your lenses.

[private]

I've only noticed it with the 24-70 - not the 85 or the 70-200 - now that I think about it...

[sk66]

I looked at the exif...lens at 35mm f/2.8....

Based upon the field of view I would guess you were not much more than 3-4 feet away. If that is accurate, the total DOF would be around 4". Any change in angle etc could be enough to shift the focus out if using the focus/recompose method. (that's why you can choose the focus point to use in spot focus, to avoid recomposing)

Still, it seems more like operator error, could be you let up on the button and it refocused, could be you weren't really in spot, could be you were in a C focus mode, could be technique (reframing, not likely), could be change in position...etc

However, if it's consistent I'd say it's a severe case of front focus.....something like 3-5 inches which is completely unacceptable. (1/3 dof in front of focus point, 2/3 behind. I'm guessing the closest element in the image is at least 6" in front of his face)

If you were further away or the focal length was really 24mm (reported as 35 effective) then it would be an even WORSE case of front focus... I hope that's not it, I've never actually heard of a case that bad... (5" would be conceivable at much longer distances and focal lengths, but not 35mm and under 20ft)

[private]

I was about 4 feet away and it seems to be pretty consistant..I will test more tomorrow- but when I do a session, I find that I am focusing onthe eyes and then moving down and those seem to bethe sharper pics...I have the 24-70 on my camera 95% of the time, but I have noticed that the 85mm is always 100% sharp - but expected b/c its a prime...

I really hope its user error. THAT I can deal with!

[sk66]

Originally Posted by private

I was about 4 feet away and it seems to be pretty consistant..I will test more tomorrow- but when I do a session, I find that I am focusing onthe eyes and then moving down and those seem to bethe sharper pics...I have the 24-70 on my camera 95% of the time, but I have noticed that the 85mm is always 100% sharp - but expected b/c its a prime...

I really hope its user error. THAT I can deal with!

Try using the focus point selection and not recomposing...it's the little button top right on the back of your camera.....

[Doug Pardee]

AF calibration on the 24-70 is known to be unusually tricky. It's possible that yours needs to be recalibrated.

Check this article by Canon's Chuck Westfall, about halfway down the article. He gives instructions on how to test if your 24-70 needs to go to Canon for recalibration or not.