Interesting focus problem on only one lens

Hi folks,

Have an issue maybe you can help with.

I have a Canon 1D MK III and 5 L lenses. 4 of these are as sharp as I could ever want, but one has never been sharp (24-70L) and I have even exchanged it with Canon. No amount of micro adjustment makes a difference.

Yesterday I met with another photographer and did some very interesting experiments. I used his 24-70 on my body and got similar results to mine. But then used mine on TWO of his bodies and it was exactly as sharp as would be expected. So I think we can rule out it is a lens problem.

What could possibly be happening in the body that would affect only one model of lens to be soft? And I worry that adjusting the body for this lens would throw out sharpness on the others which are near perfect.

Last, the body is out of warranty. I have never been happy with the quality of work from Canon Irvine. Just not great experiences. Would you happen to know of a repair center in Northern California that is trustworthy to solve this problem on my 1D MK III?

Appreciate any insight.

~Bob

If you very carefully manually focus the 24-70 on your body, is it capable of a sharp photo? If yes, then the entire problem is AF calibration of your 24-70 matched to your 1D2. The only way to fix that is to send both to Canon and have them calibrated together.

Have not tried manual focus as I find that very difficult with the standard focus screen. I can try and report back. And Live View with low pixel screen I did not find much better for manual focus.

But I'll see what I can find today.

~Bob

OK, very interesting I cannot improve by manually focusing. In some cases, I can equal autofocus, but in many not even as sharp. Hard to judge for me when focus is as good as possible manually.

However, its still morning here so shooting at 1000 ISO. Slightly better results than yesterday, maybe because of higher shutter speeds. Still would like that extra touch of crispness I get from my 24-105 or 70-200 2.8 or that I see in others shots of 24-70's online, but close - just not that last increment of sharpness that makes you not even question if anything is amiss.

~Bob

The standard focusing screen used in dSLRs is optimized for bright viewing, since some of the light is diverted from the viewfinder to the AF sensor in the bottom of the camera. The main way to increase viewfinder brightness is to make the focusing screen surface less coarse, which degrades its precision in visual focus accuracy perception. That is why accessory screens like (for 5DII) the EG-S screens are available from Canon...improves manual focus accuracy without degrading the light metering accuracy. (Most aftermarket screens improve focus accuracy while also degrading light meter accuracy.)

When you say you're not using Live View to manually focus, have you tried it at the 10x zoom/magnification? I find that quite effective on the 1D3. Sure, not as many pixels as the newer cameras, but that 10x view is pretty dang detailed.

Give that a try, but still you would benefit from having the two serviced together by Canon. Just make sure that you can get the camera to work well with your other lenses. You may need to look at using MA with some, I don't know.

If you can't MF (using Live View or a dedicated focusing screen) then I don't know what the problem may be. You said you get good results from using that other camera, so it seems like manually focusing yours should work, in case MA should work. Seriously, what other approach could you take without sending them in? I dunno!

Well, hope you get things working! It's a gread body, as you've seen with your other lenses, and the 24-70 can do really well with the 1D3! I also enjoy my 24-105 and certainly my 70-200 with it, but I'll pick up the 24-70 with it any day!

Thanks Tony. I'm leaning that way to sending them both in, maybe even with one more lens to be sure they are fall in the sweet spot. Will try Live view once more to see. I;d like the 24-70 to be my "go to" as well and it would be on my friend's bodies

Well, with the Live View approach, make sure it is wide open/f/2.8. then, you will need a surface that is flat/even with the plane of focus. With the wide open aperture, something at an angle can get out of the depth of field pretty easily, and even the 1D3s center AF can be a bit off of dead center (it's not the "point" center that the 7D has). So have your detail on the plane of focus, do an AF, then you can switch into Live View do the 10x view and see if you can MF and get a better focus on the detail.

If you can, then that would make a good case for using the MA and adjusting it yourself!

If you can't, and you don't have a reasonably good sharpness, well, try Canon...

I did have an interesting discussion with a POTN member who was unhappy with his now gone copy of the 70-200 f/2.8 IS because it was a bit soft wide open compared to, say, an f/4 wide open. Of course at f/4 the f/2.8 lens was just as great as the f/4, but still, a little bit softer at f/2.8.

Well, sure, I've had chats about that with other folks. The thing is, though, I've been very happy with my 70-200 lens! I don't shoot at f/2.8 unless I need to, sure, but when I do need to the lens gets the shot!

So, "sharpness" is partly a matter of subjectivity and perception, but in your case since the lens behaves noticeably better on your friend's body and you made sure that your shots were equal in technique, subject, etc, then hopefully you will be able to nail it down to needing MA, but...who knows?