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View Full Version : Possible Auto-focus problem 1DsMkIII


Tim Dolan (Longwatcher)
August 5th, 2008, 08:05 PM
With the usual disclaimer that I think it was something I did or am doing and not the camera.

So there I was for the first time this year and first time ever with my 1DsMkIII (21.1MP just to be clear ) shooting a model outdoors on a nice hot sunny day. Previous attempts being rainy or overcast. Not first time with camera, just outdoors in mostly sunny (as opposed to overcast) weather.

For most of the shoot the focus was dead on - far better then my 1DsMkII ever did. Also I had just finished micro-adjusting all of my lenses within a week before and they were dead on. Until suddenly for one setting the Auto-Focus basically failed me. Then when we changed location the AF was spot on again.

In that one set I think I got one in-focus shot out of about 20. The majority seemed to pick the closest object in the scene, one or two back-focused and only two got close enough, although only one was actually in the zone. The closest object in the scene was on the edge of the frame and no where near my model.

AF was turned on, I checked.
28-70/2.8L lens
one-shot mode
AV mode (because of the occasional scattered cloud)
I am fairly confident the AF point was on target, but since it seemed to focus on things outside of the AF points, it wouldn't have matter anyway. I usually by habit tend to wait for the red square to light up indicating focus lock before shooting which is why I am certain it was on target, but I am usually concentrating on getting the shot, not the camera.

BTW: Is there a way to see after the fact where the AF point actually was? I don't remember DPP having that capability and I don't know of any way in PS. Do I need to use the other Canon software?

If any one has suggestions without me posting the raw data, that would be appreciated. If you need the raw data, I will put up a couple tomorrow.

Conditions:
A path through some woods around 4PM, bright Sun (when it got through the trees), in the 90's. The difference between that scene and others was the model was just forward of a bend in the trail with a lot of small trees behind her in a very complex scene, although she was forward enough of the trees, it should have been easy on the AF. The model was wearing a white dress with medium sized black flowers on it. The model is of Asian descent.

Reason this is important to me (other then just curiosity) is we are tentatively planing on going back there to shoot something specific with a different outfit under similar conditions.

Trivia: We didn't like very many shots from that set, mainly because the outfit was wrong and then the bad focus didn't help. And I did not notice the bad focus at the time, because I am usually looking only for good exposure as far as the LCD is concerned. Also my eyes, my glasses and the diopter adjustment don't always get along and I put on and take of my glasses depending on distance. And it doesn't help my eyes will compensate somewhat for mildly out of focus optics.

first time I have had an AF problem with this camera so figure it is me doing something, but I usually shoot in the studio and having a model that shows up and the weather is nice on a outdoor shoot was a nice change from usual. But I thought it was strange that the AF messed up for that one set and otherwise worked great before and after.


Any suggestions for things to look at appreciated.

Bart_van_der_Wolf
August 6th, 2008, 08:51 AM
For most of the shoot the focus was dead on - far better then my 1DsMkII ever did. Also I had just finished micro-adjusting all of my lenses within a week before and they were dead on. Until suddenly for one setting the Auto-Focus basically failed me. Then when we changed location the AF was spot on again.

In that one set I think I got one in-focus shot out of about 20. The majority seemed to pick the closest object in the scene, one or two back-focused and only two got close enough, although only one was actually in the zone. The closest object in the scene was on the edge of the frame and no where near my model.

Hi Tim,

Strange indeed. I assume the AV was relatively wide? Were you using a single focus sensor, or 'ring of fire' auto-selection mode? Were you using normal AF or AI servo AF?

BTW: Is there a way to see after the fact where the AF point actually was? I don't remember DPP having that capability and I don't know of any way in PS. Do I need to use the other Canon software?

You can see which AF sensors were used in the Zoombrowser software, but you can also see it on the camera's LCD when you set that option in the second blue menu tab (it only works when not zoomed in). You can also see which AF points were used in the EXIF data, but that requires interpretation, you don't get a visual feedback.

Any suggestions for things to look at appreciated.

Theoretically a dust bunny or a small insect* in the mirror-box could interfere with with the AF optics/sensor. A few puffs with the Rocket Blower can usually take care of that.

*I mention this because I had one scary moment when using Life View in the 10x setting in an outdoor session which required several lens changes and optimal focus. All of a sudden I saw a huge critter running across the enlarged LCD image while focusing by hand. I freaked out a bit, because I knew that closing the shutter would lock the critter right there on the AA-filter where it could excrete its bodily fluids. I never saw it again, maybe it got caught on the sticky tape of the auto sensor cleaning, maybe it flew out with the puff of air I applied in sensor cleaning mode ...

Bart

Cem_Usakligil
August 6th, 2008, 09:29 AM
...You can see which AF sensors were used in the Zoombrowser software, but you can also see it on the camera's LCD when you set that option in the second blue menu tab (it only works when not zoomed in).
Bart, if I'm not mistaken, DPP shows the focal points as well. I do not use this feature much since I continuously use the cetral focus point to focus and then recompose.

....*I mention this because I had one scary moment when using Life View in the 10x setting in an outdoor session which required several lens changes and optimal focus. All of a sudden I saw a huge critter running across the enlarged LCD image while focusing by hand. I freaked out a bit, because I knew that closing the shutter would lock the critter right there on the AA-filter where it could excrete its bodily fluids. I never saw it again, maybe it got caught on the sticky tape of the auto sensor cleaning, maybe it flew out with the puff of air I applied in sensor cleaning mode ...
LOL, remind me not to buy your camera 2nd hand pls ;-)

Cheers,

Bart_van_der_Wolf
August 6th, 2008, 10:00 AM
LOL, remind me not to buy your camera 2nd hand pls ;-)

Gives the term sticky sensor debris a whole different meaning, doesn't it? ;-)

Bart

Tim Dolan (Longwatcher)
August 6th, 2008, 01:45 PM
Hi Tim,

Strange indeed. I assume the AV was relatively wide? Were you using a single focus sensor, or 'ring of fire' auto-selection mode? Were you using normal AF or AI servo AF?

One shot mode (normal AF), single focus sensor (I don't like the ring of fire - it missed too much with my MkII and I am usually trying to hit the eyes when closer up - especially when using my 85/1.2) I tend to like shallow DoF, which means focus has to be where I want it. Another reason I keep hoping Canon will find a way to extend the AF points out far enough for my taste


You can see which AF sensors were used in the Zoombrowser software, but you can also see it on the camera's LCD when you set that option in the second blue menu tab (it only works when not zoomed in). You can also see which AF points were used in the EXIF data, but that requires interpretation, you don't get a visual feedback.

too late for the LCD, however, after going to my older computer I found a copy of zoombrowser - all of my shots were on the face (well technically one was between neck and head, close enough)
and apparently I was taking the time to change the focus point as I usually do.

For trivia; Did Zoombrowser come with the MkIII? I don't have it loaded on my Laptop which is kind of strange, but it might just be a case of I never figured I would use it.


Theoretically a dust bunny or a small insect* in the mirror-box could interfere with with the AF optics/sensor. A few puffs with the Rocket Blower can usually take care of that.

Bart
based on this, I am thinking the dust bunny scenario seems the most likely as I remember mentioning to the model that it seemed dustier then my house as I had to clean my lenses off twice in less then an hour. I know I changed lenses shortly before that point, but I can't remember exactly when (guess I will have to look that up), but given it is quite possible the dust speck got in the wrong place for awhile and then when we moved, I maneuvered the camera enough to shake it out of the way - makes sense.

Thanks,