30D Back focusing or the photographer ?

Hi folks,

I am relatively new to the forum here, and really enjoying getting re-connected with photography. Appreciate the banter, the insight, and all of the opinions. Lots to learn.

Last week I got a shiny new 24-105L (whoohoo!) and this weekend took it out to the local links to give it a whirl. When I came home I noticed that some of the pics were back focused....so my wife hearing me curse and moan reminded me that with some of the hockey pics I had taken in the past (same camera but 70-200 lens) I had also complained about not getting the focus right (the board behind the player in focus). I attributed that to "hockey is hard" (which it is), but maybe.....

Anyway I took a look at some other articles and posts and found the good ole test charts, and took some pics with that, with both my 24-105 and 70-200. Three posts in succession, the first with a "suspect" back focused golf pic (the fence and the tree needles appear to be most in focus.

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With 24-105 at F4 (first one) and 70-200 at 2.8 (second)

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To me the charts look pretty good. I don't see any evidence of back focusing. Do you? As I understand it, the in-focus field, or the equally out-of-focus field, should lie 1/3 in front of the subject and 2/3 in back, in terms of distance. If that's right, then if anything the 24-105 may be slightly front-focused. In any case, it appears that the center point is right in the middle, which seems fine. Am I missing something?

But it is also true that focus-and-recompose DOES result in back focusing, and if the depth of field is shallow enough you'll notice it. Here's a diagram that shows why.

http://www.flickr.com …/gbhphotoarts/6​125043543/

Thanks Peabody....there were a few other charts which looked a bit worse, I'm just not familiar with how to correctly use them. Appreciate the link. I use center point focus and next time I'm out will try some other methods (like a left point in the case of the golf pic above).

It's pretty good on the charts and your sample shot is reasonable. Why not just select an aperture that gives you more depth of field?

If you don't want the background to distract, then you need to be a LOT closer to the subject and then see how it pans out.

Hard to tell without seeing the EXIF information!

- Which picture mode are you using, which focus mode?
- What was the aperture of the picture in question?
- Do you or the camera select the AF point?

On the picture in question, there seems little contrast on the golfer (apart from the white sash) and lots of contrast in the back, so the camera might have focused on the background because of a lack of a good focusing point. I have a split screen viewfinder in my 20D which helps, as I see immediately what the camera is focusing on - sometimes it is a surprise.

Have you tried using the "*" button instead of the shutter to take the shot?

Best regards,
Andy

cbadie, if you can use a focus point that minimizes the amount of recomposing, that will reduce the back focusing. I know a portrait photographer who does that. She composes first, then picks thefocus point that's closest to the eyes. The only problem with that is that the outlying focus points may not be as precise as the center point.

Thanks for all of your comments folks! I will spend some more time working on my technique including the suggestions that you provided.

Great forum, very helpful....hope that I can too pass along future postings and ideas.

Clark