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Thread started 12 Apr 2012 (Thursday) 09:35
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5D3 is front focusing with outer AF points and fast primes?

 
Invertalon
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Apr 12, 2012 09:35 |  #1

EDIT #3: I posted new test shots with a brand new 35L ( https://photography-on-the.net …p?p=14931623&po​stcount=65 ).... Seems my issue is completely gone... No AF issues at all, center or the farthest AF point to the left or right. So maybe it is not field curvature after all, but was due to the lens somehow.


EDIT #2: I believe it is not a real issue, just field curvature.


EDIT: No longer effecting just fast primes... But appears to be any wide angle lens under 50mm or so. Go to post #9 to read more about my findings.


Myself and a few others I have found on here and FM, that the 5D3 is not playing nicely with fast primes and the outer AF points. Using center focus points (center cluster), AF is perfect. It nails each and every time, wide open.

But switch to the outer AF point and the camera front focuses. This can be repeated over and over again. Switch back to center point and perfect focus.

I calibrated my 35L to my 5D3 with Focal, and it gave the results of +4 at various distances, very consistent. At that MA, focus looks absolutely perfect.

But the outer AF points (using cross only) are not near as sharp. Yet if I focus and recompose using center AF, it is sharper then using the outer points directly.

I contacted Canon and they want me to send the camera in (along with lens). I may end up doing this eventually, but I want to wait for more feedback from others if it is just isolated to a few people or more widespread. Note, it appears to happen at larger distances, not close up. Shoot something some distance away, over 20 feet or so. Up close the issue does not seem to occur.

Here are some test shots I took to show what is happening... Note, I have done this same check on many different subjects, all with the exact same result. Center is always perfect, outer much softer. The only "resolution" is to increase my MA to +10 or so, but the center then becomes softer. Using live-view as well towards the edge results in a very sharp image at the edge of the frame, so I know it is not field curvature or anything like that. It is just an AF issue.

Here is the full image:

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Center AF crop:

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Using far left cross AF point:

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Using Center AF again:

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Focus Recompose to same point as edge cross AF point:

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Like I said, this is only one example of what is going on... I have checked it over and over and it is repeatable very easily. On FM I read about two or three having the same phenomenon happen with the 50L and 35L. As well as one or two people here so far.

Just want to see if any others have this problem... If it is very isolated I will just send my stuff to them next week, let them find out why it is acting the way it is. Using the outer AF points with my other lenses have had no issue what-so-ever. It strictly is confined to the 35L.

-Steve
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MatthewK
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Apr 12, 2012 10:50 |  #2

Corroborating what was said above... my 50L is experiencing the same issue, with the outer points front focusing by a good amount while the center points are spot on. I had spent quite a while MFA'ing the lens (it's my favorite lens, so it got the most MFA time :) ), went out and shot, only to have it front focus from distances of ~15+ feet. So I dialed in some adjustment (from +7 to +15), and the outer points were hitting, but center was way off.

My 50L performs flawlessly on my 5D2, so I know it isn't a lens issue.


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pyrojim
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Apr 12, 2012 10:53 as a reply to  @ MatthewK's post |  #3

Well,

I imagine that for your money, you expect perfection(as I expect perfection from anything I spend more than 250 bucks on)

So, I wonder if you are experiencing a curved plane of focus....


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bobbyz
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Apr 12, 2012 11:12 |  #4

I assume if you MA with outer points you get different value compared to when using center point.


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Invertalon
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Apr 12, 2012 17:38 |  #5

It is just weird that if I focus and recompose, that the sharpness is extremely good. As soon as I try to focus using outer points, it is front focused. So I don't think plane curvature or anything like that is happening. If anything, it might deal with the AF system and how it interprets the light from faster lenses on the outside points?

Just sucks because I love using wide fast lenses with outer AF points (big like with the 5D3), but if it front focuses all the time, then it is not helping me. I may end up sending it in if the next firmware doesn't address it. Let them found out why it is acting the way it is. I highly doubt it is the lens because then center AF would be off as well, but who knows... And the fact others are getting the same thing.

I do notice if I push the MA back to +10 from +4 (calibrated setting), that both outside and center are both good sharpness, but the center AF point now shows more purple fringing (focus plane pushed too far back). So it is either deal with more fringing at the expensive of more reliable outer AF points, or go for maximum sharpness of center AF point but have almost useless outer AF points. Kind of sucks.


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John ­ from ­ PA
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Apr 12, 2012 18:37 |  #6

To the OP, I see you shot at f/1.4 with the 35 mm; The calculated DOF at 20 feet is 8.78 ft (assuming circle of confusion at 0.03m). Are you sure the focus isn't being fooled by something? When you use center point, and see something around 20 feet on the lens barrel, what distnace do you see after switching to a different focus point.




  
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Invertalon
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Apr 12, 2012 18:46 |  #7

The subject from where I took the shots according to the DOF is just at/under infinity. Switching to the outside AF point, you see the DOF scale jump on the same target closer to 10' mark on DOF scale. And not exactly by a small amount either, it is quite a jump. It is really strange. Happens with left or right AF points. Center is consistently at infinity line. Outside closer to 10' on scale (but more then).

Close up it does the same behavior... I did something about 2.25' away... Center locks on at that point one after another, switch to right or left AF point and it jumps to the left about .25" I would imagine. It is not a tiny bump.


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JeffreyG
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Apr 12, 2012 18:47 |  #8

I do not have this issue with 24L II and 85L II. I have not shot the 50L enough yet to know either way.


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Invertalon
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Apr 12, 2012 19:03 |  #9

I just slapped my 24-105 on and found it does the exact same thing. So it is not just limited to my 35L.

Doing the same test (tripod mounted) I see the AF front focus when I use the outer points versus center. DOF much greater at f/4 to f/1.4 so that is why I am seeing it more. I don't see it happen at longer FL like I do at 24mm on the lens. So it may have something to do with focal length and outer AF points?

But yeah, checked my 24-105mm at 24mm with near and far targets... AF point changes quite a bit from center to outer AF points. Can clearly see it on the DOF scale.

The higher the FL, the less change I see. Under 50mm seems to show it best.


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bobbyz
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Apr 12, 2012 19:06 |  #10

It is for distance objects like in your picture or for even closer objects?


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Apr 12, 2012 19:06 |  #11

I haven't noticed this with my 35L... But I will have to check it more closely...


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Invertalon
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Apr 12, 2012 19:18 |  #12

Both close and distant subjects. Happens with both my 24-105L and 35L now. AF on a subject (tripod) with center point, shift the tripod so you are now on an edge AF point and try again... My DOF scales shift to the left (front focus).

Again, it appears to happen under 50mm or so. The telephoto end of my 24-105 seems to be more consistent.


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Hitthespot
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Apr 12, 2012 20:02 as a reply to  @ Invertalon's post |  #13

This is so disappointing to read, especially if this turns out to be widespread. I am so sick of my 7D focusing issues that I told my local pro shop to get me in a 5D3 body. I swear if I have any more focusing problems with Canon bodies/lens I'm moving back to Nikon.


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Invertalon
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Apr 12, 2012 20:07 |  #14

I did more testing with Focal targets on a well lit-wall, with the camera on a tripod and two targets placed at center and outside cross AF points. Eliminating all camera movement error that can occur.

With both 35L and 24-105L the DOF scale jumps quite a bit just by switching the focus point to the side. I also checked with other targets and stuff and the shift is consistent. It appears to move the focus point more the farther the subject is away. It is quite a big difference when the center point locks in at near infinity (perfect), yet the outside AF point shifts the focus away from infinity closer to the 10' mark.

Again, I tested with my 135L and no shift occurred. It appears to happen with wide angle lenses only, below 50mm or so for whatever reason. Field curvature? I don't know. I am guessing something with how the light rays enter the AF module with wide angle lenses (my theory). But yeah, seems to not occur with longer FL lenses (or be that much of a concern with 'slower' lenses). My 24-105L still looks sharp after the shift due to the greater DOF. But the 35L shows pretty badly.


-Steve
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Gregg.Siam
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Apr 12, 2012 20:25 as a reply to  @ Hitthespot's post |  #15

I just tried this on my 5D3 w/24-105 and didn't have any difference in focus. At 24mm and 105mm both the center and out AF points had the exact same focus.


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5D3 is front focusing with outer AF points and fast primes?
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