canon 24/70 2.8L - opposite points focused

skruf88

I'm having big time problems,
Yes yes I know, soft focus problems on lens' have been posted to death on these forums and most of what comes back from responders is "operator error" but....
Here's some back ground. I am using a Canon Rebel XT that I got a year ago and decided to spring for good glass before I upgraded cameras. I have a studio where I work and use fixed hot lights so I opted for a good low light lens. Went for the Canon 24-70 2.8 L series. I had been having soft focus issues with my old lens and thought this would fix it. To my dismay I still have the same problem, even in bright sunlight. I would say only 20% of my shots are in sharp focus.
-I am not new to photogaphy. I do know how to use my camera specifically the focus points and I have 'read my manual front to back' just in case that was a suggestion.


Here is something I noticed today. I did a shoot with a model in full sunlight, set the focus points on his face. Shot at 100 iso, 1/200s - f7.1 at 45mm.
I noticed that in most of the shots, the exact OPPOSITE focus point is was in focus while his face remained soft or blurred. As I go over my past photos I'm noticing the same.

On other thing I have noticed, when I use AF when the lens is fully zoomed out, and I zoom in to check the focus, it is often blurry. Have used the technique in the studio on tripod of zooming in to lock focus, then zooming out to take the shot. (just a side note)

Questions-
is this a camera or lens problem?
Has anyone experienced this with either the Rebel xt or new canon lens'?
any cordial responses are most welcome!
Here is a link to a few examples, both shot with similar exposure.
http://www.themaleimage.com/focus

Thanks,
Joe

ivar

Hi Joe, welcome to dgrin

Pictures say a thousand words you have a sample or two with EXIF?

Also, what exactly do you mean with the 'opposite' point? Do you mean the focus points of the camera? Say that you select the most right one, and it focuses on the left one?

The 24-70 is supposed to be parfocal (I can use that big word now, as I just learned what this meant in another thread), but for some reason I never trust setting focus and then zooming in and seeing if it is still in focus. Just a feeling though, maybe others have some thing better to say.

See my signature below on how to do most anything here. Questions? Ask them

claudermilk

Since you say you are having the same problem with two lenses on the same body, I would think it's pretty obviously a problem with the body. In that situation, I'd take it to Canon & have them check it out. You've got a pretty detailed descriptiopn of the problem, so should help them troubleshoot.

Like Ivar, even with parfocal lenses like the 24-70, I still prefer to double-check focus after zooming--especially using it wide open since the DOF at f2.8 is pretty narrow. Of course, I cheat a bit with my KatzEye split prism screen, too.

skruf88

ivar wrote:

Hi Joe, welcome to dgrin

Pictures say a thousand words you have a sample or two with EXIF?

Also, what exactly do you mean with the 'opposite' point? Do you mean the focus points of the camera? Say that you select the most right one, and it focuses on the left one?


Hi Ivar thank you for the reply. - There is a link on my original post to two examples of my shoot yesterday if you'd like to take a look.
http://www.themaleimage.com/focus
These photos were shot at 100 iso, 1/200s - f7.1 at 45mm.

as far as the 'opposite point' of focus: If I'm shooting in portrait and the camera is now turned on it's side, I choose the focus point closest to the top so that the subjects face is in sharp focus...correct in theory right? But often times when I look at the photos, it's the bottom of the photograph that is in sharp focus while the top is blurred. It's a strange problem and seems to happen more when the lens is zoomed out. In fact, auto focus on this lens is really unreliable when the lens is zoomed out.

I'll take a look more at how to work with a non parafocal lens, that's new info to me and looking forward to seeing how to work better with one, but any advice is welcome.

I did take a look this morning at my old lens and it does seem to pick the proper focus point in portrait mode. (canon's zoom browser will show which focus point was chosen) It just seems like the 24-70 whether I shoot manual or auto focus, will end up focusing on the point at the opposite end of the view finder (even if the correct point lights up when I focus)

Joe