Someone posted here about using a hot mirror filter fixes the problem. I know that RG said that UV filters don't help but a hot mirror makes a considerable difference to the wavelength of the light hitting the AF sensor and kills all the IR present in the warmer light which hot and sunny weather brings. I know that Pentax people found that this cured a lot of their focus problems, it might be worth seeing if more people could report back on whether it helps.
Nill,
I believe it is a filter that will remove IR light, it is also called IR cut fillter. I am using those filters for lenses on my Leica M8 to get rid of the ugly purple shift.
BTW, did you guys notice on the poll that the ratio of having AF problems to not having AF problems has shifted? For the first time, the number of people that did not experience any problems is higher now. Since you can vote only once, I started to believe that the early copies had quite a few of bad apples or that the newer bodies were further tweaked by Canon. I voted "not sure" before but now I am ready to jump to the "not noticing any AF problem" camp but I can't....
Nill,
Just did a search on B&H. Tiffen makes a Hot Mirror filter. 77mm is $179. God does it ever end. If this is the fix and you have a few different sized lenses the price seems to stay at around $179.
Rob Eckert
Isn't this funny. A few years ago people complained that the Hot Filter glass in front of the sensor was creating sharpness issues. Companies responded by reducing the strength or eliminating the hot filter altogether. Color shift issues have become a problem. Highlight ghosting on some cameras. Now a possible focus issue with the MkIII. That is the reason I just hold on to my MkII. Great camera and I know its quirks. I can work around them. I hate how many companies today practically use the public as "Beta Testers". Camera companies are not the only ones doing this.
Rob Eckert
I have had problems fitting some screw on filters into the slot of my 300 IS when mounted onto Canon's holder. I used to use only "thin filters". Problem is many filters are not available in the thin version. If I recall correctly Tiffen is already on the thinner side. My drop in filter holder originally came with this thick Canon filter that did not even fit into my 300 IS slot. Go figure.
Rob Eckert
This was posted to a different site, but I thought folks here might find my experience useful. This is the first time I have posted here--it's the first time I have had anything worthwhile to add to this excellent forum. Are there bad units in the wild? Yes. My 1D Mark III just shipped out to Canon CPS per their request following my description of my Mark III's AF problems.
I normally assume I am at fault when my results are sub par. That assumption is what made me keep this body beyond the time limit for returning to the dealer. First, I noticed many unsharp results amidst some stunningly detailed frames. Although not limited to telephoto shots, the soft results dominate my telephoto frames (70-200 F4 L IS & 300 F4 L IS).
Trying to sort this out, I was unable to get any sharp frames of oncoming traffic--but speeding trucks really slow down fast when you point a camera at them. Needing a more repeatable test, I have done a ridiculous # of test series of my wife riding toward me at 10-15 mph on her bike (in hot and cool, sunny and cloudy weather). The results? Nine gigabytes of distressingly out of focus boring pictures.
Had I suddenly lost all my photographic ability? Did I not know the magic CF combination?
OK, I needed a more controllable & objective test. Out came the metal yardstick and focussing chart. Crude, but very enlightening.
With the MKIII on a huge old Gitzo 'pod and Arca Swiss monoball head & focused on the 8 in the #18 on the angled yardstick at 45 degrees, I ripped off a burst at 10 FPS. Viewed on the monitor I watched focus shift, frame to frame, from back focus to front focus in the burst series. The series was shot in AI Servo, Center point with no focusing point expansion on. Focus shifted from almost #16 to #19(camera approx. 10-15 feet from ruler). These results were repeatable with two different 70-200 L lenses(yes, IS was off) and the 300 lens. The same lenses on my wife's 20D in the same test yielded (repeatedly) virtually no variation at all.
Next a focussing chart was used, again tilted 45 degrees to the camera's focal plane. The results with each of the three lenses showed focus shifting from front focussing to back focussing by as much as 2-3 inches. This occurred in single shot, non-Servo mode as well as 10 FPS bursts in AI Servo mode. In some series, focus would shift from pronounced front focus to pronounced back focus in just two frames. The focus shifting was very repeatable except the degree and direction varied from series to series. The new focus microadjust feature can't cope with variable focus shifts. Neither can I. Next week I should know if Canon CPS can resolve this problem.
For me, this proves that some MK IIIs are indeed "bad". I don't question for a moment that many others have perfectly wonderful MK IIIs. But for those of you who are unable to come even close to results with other bodies, you too may have a MK III that keeps guessing where to focus.
You're welcome. My Mark III was beyond my expectations in every other respect. When Canon resolves the focus issue for those of us that are plagued with it, I think this will be the best all--around use camera available at any price point. The live view feature with magnification has already been a tremendous help when shooting Tilt/Shift shots for stitching together for one of our Calendars. Short of the focussing issue, the MarkIII gives the best image quality (including for large prints) I have yet experienced.
Are you saying the camera focus would move even in single shot AF when a burst was triggered? Could you explain the single shot focus shifting, I'm not folowing that one.
The focus moved in single shot non--Servo mode and in 10 FPS Servo bursts. In single shot, non--Servo mode, if I defocussed the lens then refocussed with AF (center point and no expansion), the focus would shift on the majority of shots, often dramatically. These tests were done carefully with a monster Gitzo 'pod and not altered/moved between exposures. On one hand this flabbergasted me, on the other hand I was relieved because it confirmed what I was seeing in the field, and I had not completley lost my mind and/or photographic ability.
Yep, I have proved to my satisfaction that at least some of the AF problems being reported are very real. What makes this so maddening is that the camera is so outstanding in every other respect that I don't want to be without it. The sum of its abilities and superb image quality is greater than a simple recitation of its improvements. I find myself being more adult about this than I would have expected--so far. I'm waiting (brieifly), hoping that Canon CPS resolves this quickly.
but I can't....