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Author Topic: 5D Mark III focus points off center  (Read 7467 times)

Mt Spokane Photography

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Re: 5D Mark III focus points off center
« Reply #15 on: May 15, 2013, 02:29:27 PM »
You do realize that the AF point itself is not (1) pixel.. It is an array of many pixels in that given area, however during autofocus the camera can determine best focus based on the contrast in an area of just a few pixels depending on the actual subject/scene.

Basically what I mean is lets say under each focus point there is a grid of 100 pixels - and when focus is achieved under the selected focus point it happens to be on the right side of the 10x10 grid of pixels - then attempting to place a marker that represents the square/dot seen in the viewfinder precisely over the actual focus point in an image it is going to be off to the right of the super-imposed point in the viewfinder.

Well, let me give you another example. If I place the small focus point on someone's eye ball using the LCD & then check the viewfinder and see the point on his/her nose, which one am I focusing on?

I'd say that the LCD is more likely to be accurate. Therefore if I use the viewfinder to focus, I will not place the focus point on the target I was aiming for.
Liveview Quick Autofocus is likely to be less accurate.  It takes the image off the sensor, but the AF points displayed are electronically generated and have nothing to do physically with the AF sensor.
I'd expect the viewfinder to match the AF sensor, if it doesn't, Canon can adjust it, its likely not seated correctly.
 
In any event, its not likely to show up in real life because the actual AF areas are larger than what you see.

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Re: 5D Mark III focus points off center
« Reply #15 on: May 15, 2013, 02:29:27 PM »

neuroanatomist

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Re: 5D Mark III focus points off center
« Reply #16 on: May 15, 2013, 02:36:27 PM »
Yes but it sounds like he is comparing the viewfinder square with what is displayed on the LCD screen on the back.  They are two different things not linked together...at least not on the 5D3.

The red AF point markers on the rear LCD are not tied to the point in the viewfinder...though they attempt to show you which AF point was activated during the shot, they are not calibrated to the PD sensor.

Sounds like he's comparing the selected AF point with the red marker displayed during image playback (with that function enabled).  While they're not 'calibrated' if the center AF point was used, that red marker will be dead center in the image.  If the shot was taken with a feature under the center AF point, and that feature isn't under the red box on review, there's a misalignment.

Note that it should be tested properly - on a tripod, etc., since if the camera is moved between half and full shutter button press (unintentional focus/recompose) the camera doesn't know that (unless it's a Hasselblad) and that will appear as misalignment.

I doubt that these two modes have separate AF systems with different AF point locations.

Your doubt is misplaced.  Phase detect AF (viewfinder) uses a dedicated AF sensor, whereas contrast detect AF (live view) uses the image sensor itself to determine focus (which takes much longer).
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Dick

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Re: 5D Mark III focus points off center
« Reply #17 on: May 15, 2013, 03:01:59 PM »
Thank you guys for explaining! I guess I can just cancel the scheduled repair then.
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Skulker

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Re: 5D Mark III focus points off center
« Reply #18 on: May 15, 2013, 04:45:06 PM »
Thank you guys for explaining! I guess I can just cancel the scheduled repair then.

I've been away since my initial reply, work getting in the way again.  >:(

As others have said the focus in live view is completely independent of "normal" focus, they are different systems.

One point that has not been mentioned is that when focusing using live view you can move the focus area! Also the size of the focus area changes! You can move the focus point with the joy stick and zoom in with the zoom button. Sometimes in live view if you can't focus at one zoom setting then you can with another.

Live view focus is normally more accurate and much slower. (Although the 5D3 has really good focus so there is not so much difference.)

Hope this helps.
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Re: 5D Mark III focus points off center
« Reply #19 on: May 15, 2013, 08:48:14 PM »
I had exactly the same problem and it was real.  After three service visits they exchanged the mirror box. Atfer that repair the AF points' misplacement was corrected however since then I struggle with AF system. Since almost a year from purchase the camera is being serviced all the time without any good solution. My guaranty is almost over and the camera is like piece of crap. I can only suggest you to push the store to exchange it as probably any service will not fix that. I checked 3 canon services and every time if one thing was corrected the other one was not working properly. Right now center and left points are backfocusing and right points are focusing in opposite direction. One year of frustration without taking photos. Unfortunately IMHO if you think your AF points are misplaced-you are probably right. In my camera when I focused on the edge of any target it focused far away. And it was obvious that it happened only in one edge of focus point. It is normal that the real focus point has more area than its layout in viewfinder however not only in one direction. As I said-they fix this but camera probably lost all factory tolerances and now AF is just useless.
« Last Edit: May 15, 2013, 09:01:58 PM by Martin »
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East Wind Photography

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Re: 5D Mark III focus points off center
« Reply #20 on: May 15, 2013, 10:29:32 PM »
Wow, I fortunately do not have any problems like that.  All AF points are dead on with my copy.  I use Reikan FoCal to test ALL of the AF points and it will give you a heat map of the AF points and the calculated AFMA for each point.  It takes a LOT of shots to map all of these on the 5D3 but if you suspect something is off, run the test and send a copy of it back with the camera to Canon.  I would imagine if you complain enough and it came back worse than it was, they should give you another one...or at least a refurbished unit rather than blow you off.  With enough pushing they should take care of this even if the warranty is about to expire since the issue was reported while it was STILL under warranty.

I would press them for a replacement and keep pressing until they do it.

To be honest I've never heard of this issue from anyone else.  Yes in some cases some of the AF points are off by 1 or 2 AFMA but in normal use you dont even notice that with most lenses as the AF variance is often more than that from one shot to the next.

I had exactly the same problem and it was real.  After three service visits they exchanged the mirror box. Atfer that repair the AF points' misplacement was corrected however since then I struggle with AF system. Since almost a year from purchase the camera is being serviced all the time without any good solution. My guaranty is almost over and the camera is like piece of crap. I can only suggest you to push the store to exchange it as probably any service will not fix that. I checked 3 canon services and every time if one thing was corrected the other one was not working properly. Right now center and left points are backfocusing and right points are focusing in opposite direction. One year of frustration without taking photos. Unfortunately IMHO if you think your AF points are misplaced-you are probably right. In my camera when I focused on the edge of any target it focused far away. And it was obvious that it happened only in one edge of focus point. It is normal that the real focus point has more area than its layout in viewfinder however not only in one direction. As I said-they fix this but camera probably lost all factory tolerances and now AF is just useless.

Dick

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Re: 5D Mark III focus points off center
« Reply #21 on: May 16, 2013, 12:41:24 AM »
I had exactly the same problem and it was real.  After three service visits they exchanged the mirror box. Atfer that repair the AF points' misplacement was corrected however since then I struggle with AF system. Since almost a year from purchase the camera is being serviced all the time without any good solution. My guaranty is almost over and the camera is like piece of crap. I can only suggest you to push the store to exchange it as probably any service will not fix that. I checked 3 canon services and every time if one thing was corrected the other one was not working properly. Right now center and left points are backfocusing and right points are focusing in opposite direction. One year of frustration without taking photos. Unfortunately IMHO if you think your AF points are misplaced-you are probably right. In my camera when I focused on the edge of any target it focused far away. And it was obvious that it happened only in one edge of focus point. It is normal that the real focus point has more area than its layout in viewfinder however not only in one direction. As I said-they fix this but camera probably lost all factory tolerances and now AF is just useless.

Sounds scary. I guess I'll have to discuss the issue once again with the service. They suggested that they'd move the viewfinder inside the body so that the points get aligned. To me this sounds like fixing a problem with another one and most likely doing more damage than anything else. If they mess up the AF, a serious problem is created to replace the possibly cosmetic one.

Now that I checked the issue again, I can also see (with the grid on) that the grid lines are longer on the right than on the left side of the frame. This tells me that the viewfinder might actually be in place but the indicated points are off center. ... Well, I don't know. I use cameras to take photos. Someone else can repair these things, but I hope that the someone also knows what he/she is doing while at it.
« Last Edit: May 16, 2013, 12:54:48 AM by Dick »
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Re: 5D Mark III focus points off center
« Reply #21 on: May 16, 2013, 12:41:24 AM »