I had an interesting experience - I had the 1DsIII set up on a tripod for an interior shot of a room with the 16-35mm at about 18mm and f/8. I had the center focus point selected on a fairly high contrast object, and pressed the focus on button. The center focus point lit up, the camera beeped. Then, before I could release the focus button and take the shot, another focus point to the lower left of center lit up and I got another beep as the camera shifted the focus. I was a bit taken aback. I double checked my settings and tried again. Same result. In fact, I repeated this several times. This second, unselected, focus point was over a very high contrast element of the picture - much higher contrast than the original focal point (which still had plenty of contrast to focus on and was no where near this new point).
Now I double checked everything again. The camera was in single (quiet) shot mode. I had selected the center focus point only (not the all points automated group). Auto focus was set to one-shot.
To me, it seems like this might be related to the behavior described for auto focus mode where the center focus point is used to initiate focus, then the outer points are supposed to be used to maintain focus on the initial object. This is the first time I've seen this happen, but I wonder if it could be related to the problems some people are having focusing with the 35L.
Not exactly.. But my 1D MK3 (not S) will do something similar but without the second confirmation. It'll lock on AF point, then arbitrarily focus on something more contrasty in the image no where near the AF point. For me, typically it's grass or something at the bottom of the image.
Here is an example recently... with the 16-35 as well no less.
I did actually... Not in the same condition, but had noticed that sometimes it'd shift it out of focus on another area. I disabled the expanded points. Works like I expect it to. ^_^
With AF Point Expansion enabled the camera can at times (when there is something of very high contrast near the selected AF point) shift to one of the non-selectable AF points that immediately surround the selected point. Disable AF Point Expansion to preclude this happening by setting C.Fn III-8 to 0.
Geofn wrote:
With AF Point Expansion enabled the camera can at times (when there is something of very high contrast near the selected AF point) shift to one of the non-selectable AF points that immediately surround the selected point. Disable AF Point Expansion to preclude this happening by setting C.Fn III-8 to 0.
In theory, the expand points are only supposed to activate once AF lock has been lost on the selected point, at least that is what I read in one of the white papers.
Overall it works for some things like saloon racing cars (with windscreens) but I find it doesn't work terribly well on open wheeled single seaters, more often that not it will be the rear wing that is in focus. YMMV
Geofn wrote:
With AF Point Expansion enabled the camera can at times (when there is something of very high contrast near the selected AF point) shift to one of the non-selectable AF points that immediately surround the selected point. Disable AF Point Expansion to preclude this happening by setting C.Fn III-8 to 0.
Mine does it with expansion set to Disabled. Doesn't light up, but definitely focuses on something other than selected AF point at times.
stanj wrote:
Do you have AF point expansion turned on?
No - but even if I did, I think it only expands to the sensors immediately surrounding the one that originally acquired focus. This was two 'choosable' sensors away.
apdieb wrote:
Mine does it with expansion set to Disabled. Doesn't light up, but definitely focuses on something other than selected AF point at times.
I almost missed the other point lighting up - it was just a very brief flash. In fact, I didn't really know what it was I saw the first time and it wasn't until about the third try that I was convinced that is what was happening. I wonder if, under different conditions, the sensor might not light up at all but that focus would still shift.
Again, the second focus point was a selectable point far away from the center, not a non-selectable one immediately surrounding it.
High(er) contrast than the selected AF point has been my nemesis as well. I'll select an eye in the studio, but will get high contrast hair or shoulder speaghetti strap instead. It's a pain, obviously.
It doesn't look like I'm the only one with a similar issue. I wonder if there is something wrong that we're all doing, or if this is a software problem. I know it's easy to blame it on software, but I want to make sure this isn't something I can correct myself. I'm sure it would be easier for me to change than it will be for Canon in any case.
I had some increadibly frustrating problems with focus while doing Birds-In-Flight recently - problems that I never had with the 1DsII, but I think a lot of that may be due to all the custom functions that allow me to tune, or mis-tune, the system for a particular situation. I'm thinking that this may be a consequence of something I've done unknowingly, but if so, then I'm not alone.
Is it possible when you pressed the release the camera shifted a bit and first point became less contrasty than the second? Could you test it with a cable release?
Given that it only happens to me with the new 1 series, and not the 5D, 30D, XT or D3 that I've also used in the last 4-5 years, I'm thinking it's the camera's new 'better' AF module at work.
jerrykur wrote:
Is it possible when you pressed the release the camera shifted a bit and first point became less contrasty than the second? Could you test it with a cable release?
No - it was tripod mounted and on a hard floor. In rechecking the phenomenon, I made sure nothing was moving. Besides, only the center focus point was selected and this jump was to an outer point.
Numfar wrote:
Given that it only happens to me with the new 1 series, and not the 5D, 30D, XT or D3 that I've also used in the last 4-5 years, I'm thinking it's the camera's new 'better' AF module at work.
It sure seems that way. I never saw this behavior in either the 5D or 1DsII - but then again, you can't prove a negative through observation.
I saw it regularly on the 1DMkIII and it was one of the camera's "features" that drove me to have psychotic episodes in which I would fantasy about doing dastardly things to a wide rage of Canon employees. Fortunately, I have not seen it with my 1DsMkIII.
I think there are two different ways to look at this (or a combination of them):
1) Your cam could be malfunctioning. I had all kinds of weird, erratic and random mis-focus issues with my previous 1Ds3. Nothing helped, including calibration of the body. In fact calibration only made things worse. Canon swapped my "bad" 1Ds3 for a new one that performs fine, unless I screw up myself. Basically all the 45 AF points are part of one big AF sensor. So in theory focus could jump from one AF point to another. But it obviously isn't suppose to happen like that if you didn't order it to do so. Therefore, the jumping around of focus could point towards a possible malfunction, either software or hardware related. I would contact Canon about it.
2) It could also be that your 1Ds3 is functioning fine, but that you are confronted with some of the mkIII AF "weaknesses". I have found (on a proper working 1Ds3) that there are some situations where there is a bigger change of mis-focus in AI Servo and One Shot (and when this happens, it is consistent/repeatable under those same circumstances):
- When trying to focus through windows
- When trying to focus with (strong) backlighting
- When using outer AF points with wider apertures on wide angle lenses (it doesn't handle field curvature -and the low contrast that goes with that- all that well)
- When shooting low contrast subjects surrounded by busy backgrounds
- When the area of focus has low contrast and the AF point totally covers the entire area
- With infinity focusing on small and low contrast subjects
- When the body/lens isn't calibrated/micro adjusted properly
All these possible causes (well except maybe for the last one) for mis-focus seem to be related to how the mkIII AF handles low contrast situations. Maybe one (or more) do apply to your situation?
BTW Do you have a photo to illustrate the problem?
You said: "Then, before I could release the focus button and take the shot, another focus point to the lower left of center lit up and I got another beep as the camera shifted the focus."
What do you mean by releasing the focus button? Are you using the AF on button to focus and then releasing it or are you using it to lock focus after half pressing the shutter (is cfn IV-1 set to 1?) and then losing focus? What's your setting for cfn IV-2 which switches the AF ON and * functions? How about III-10? Do you have a registered AF point selected?
The only thing I've set of these settings is IV-1 to 1 so I'm not experienced in playing around with them but it seems to me if it's not the result of opertion in relation to one of the above settings there's a problem with the camera. I think some have found defective sensors when they've had the camera sent in for service.
apdieb wrote:
Mine does it with expansion set to Disabled. Doesn't light up, but definitely focuses on something other than selected AF point at times.
My 1D MkIII as well, but I have seen the 'extra' adjacent AF points light up randomly (usually it doesn't do this, but sometimes it does, for no reason apparent to me). It's one of the things that made me believe that other (assist) AF points are being used, even if they shouldn't be, CFn-wise.
Jeff
PS: Canon's documentation on what these 'new' AF Assist points actually do is sorely lacking. It really makes you wonder what's going on under the hood.
