5DIII stopped focusing a few times on last shoot :( :(

My very reliable 5D3 would not focus lock maybe 10 times on the last shoot, with the 70-200F2.8 L IS USM II.

I noticed the lens had become slightly unlocked. I had this once before. Basically being left handed I realised when holding the combo by the lens ( which I always do ) the pressure of my hand, sort of slips and puts pressue - on the unlock button, it can be just enough, to let it start to unlock due to constantly swapping between Portrait and Landscape mode. I think its because I normally shoot with the tripod ring attached when hand holding it. ( cant reslly see a way to remove it - does it?

Before just half unlocking it and relocking it instantly stopped the problem.
But this time it seemed that I had to twist it to and fro a couple of times ( within the very slight play once locked ).
There is the small chance, that I had been using one of the outer AF points , and under the stress of it not working; I forgot that, and I was looking for it to AF on the centre point - we were doing some low light work, so there might have not been enough light to AF, i.e. A dark room with the model only partly illuminated by flash, so to left and right were very dark under the modelling lights of the flash. I thought I would mention, that as when I got home it locked on instantly everytime ( except it can't focus on the fine mesh of the Loewe speaker grill on the TV?? ( not sure if this is new as I never tried it before - it can focu like lightning on the raw silk curtains? Odd )

Q1. I suppose it could be a dirty contact between the lens and the body. But this seems strange, I as I now very rarely take this lens off the camera at all, so there is little chance of it getting dirty. In these circumstances Is it likely to be a dirty contact? ( or dirt due to wear )?

Q2 Note this 70-200 F2.8 L II lens was never super tight. When one puts it on, it twists to the lock position very smoothly, with no play whatsoever from the camera body. When the lens is first engaged, there is some play for half the locking twist distance, then for the last half of the locking twist rotation, one can feel its tightening up with no play; it then feels a bit like a perfectly machined and polished bearing with thick cold grease on it, so a slight bit of 'drag/resistance' - but when you hear it snap locked. It is not rock solid - one can rotate it back and forth maybe 0.01mm ( this is difficult to assess, maybe a better description is, "it doesnt lock to an imovable position" ). As for being pulled tight to the camera - there is no play whatsoever.
It has always been like this.
My 70-300L feels almost the same. Except that, as soon as you start the locking twist it feels secure ( no wobble) the last 1/2 of the locking twist is slightly tighter than the 70-200 L. But the 40 mm pancake seemed even slightly tighter than the 70-300L when I first got it, and is now still ever so slightly tighter.

The 70-300L also has the same sort of rotational play as the 70-200 L once locked.

Is this normal or should it lock to an immovable position i.e. No rotational play whatsoever.?
Is your 70-200 L F2.8 II wobble free for the whole lock up twist, or is it like mine just wobble free for the last 1/2 of the twist?

My EF 70-200 MkII has no rotational play, however, pulling it up and down, I can feel stopping against the body, although there is no movement on the lens. My EF 24-70 MkII fits more snugly. Of course no AF issues. I have had it stop AFing if I pick the wrong range (i.e. 2,5 m MFD) and I try to AF on a subject less than 2,5 m away. Heart stops a bit and then I remember.

The collar comes off, loosen up the screw completely and then work to take it out from the back...

Thanks for your post, useful to know.

I may have discovered the problem, by testing to see if it was AFing properly after cleaning the contacts.
I discovered it would not AF when zoomed in on my tv grill. I then tried it on my speaker mesh grill - same thing ??
During the shoot we used a voile mesh curtain as a backdrop. I had some similar voile and tried it on that - same thing , it would not lock. Yet it would lock on a speck of fluff on a velvet carpet.

I Think it was a coincidence that my hand partially unloocked it, and when Imrelocked the lens, I must have been using an outer AF point - so when trying to focus on the model with the non-illuminated center AF point, it was actually trying to focus on the voile.

This does raise another point has anyone ever has an issue on focusing on flash mesh voile. I did notice on both difficult to focus surfaces that for a fleeting moment Imwould see a sort of moire type of shimmer. I managed to recreate it a few times and my changing the zoom a tiny bit or even the angle it would lock. So its sort of like by using the technique to avoid moire, the lens can then lock.

Very strange as the lens will lock like lightning on just about any other surface, it just doesn't seem to like very repetative close mesh type surfaces?

At least I can now avoid the problem but is this normal?

Re unlocking the tripod mount I stupidly forgot to line up the red dots before withdrawing it from the back :-/

I have no problem focusing on my speakers' fine mesh even with the terrible light in my study (f2.8, 1/100, ISO 12800). Just tried it.

Submariner wrote in post #17433518
Very strange as the lens will lock like lightning on just about any other surface, it just doesn't seem to like very repetative close mesh type surfaces?

That's not very strange, that's rather very likely.
The AF system detects edges in the subject. If the lens if perfectly focused, the edges line up on the AF sensor. When it's not in focus, there's a shift in the edges. They don't meet on the sensor. By measuring how far apart they are, and in which direction, the AF system can caluclate how much to turn the lens to get it in focus. But when attempting to focus on a subject which has repetitive edges, it's difficult for the camera to assess which edge should match which.

It's a bit like taking two combs, place them against each other and then look at them through a 2 cm wide slit. Now move one comb a bit to the side. While looking through the slit, it's very difficult to figure out if you are off to the left or to the right, and by how many notches. It's the same for the AF system.

MakisM1 wrote in post #17433670
I have no problem focusing on my speakers' fine mesh even with the terrible light in my study (f2.8, 1/100, ISO 12800). Just tried it.

Thanks for letting me know - appreciated.

apersson850 wrote in post #17433811
That's not very strange, that's rather very likely.
The AF system detects edges in the subject. If the lens if perfectly focused, the edges line up on the AF sensor. When it's not in focus, there's a shift in the edges. They don't meet on the sensor. By measuring how far apart they are, and in which direction, the AF system can caluclate how much to turn the lens to get it in focus. But when attempting to focus on a subject which has repetitive edges, it's difficult for the camera to assess which edge should match which.

It's a bit like taking two combs, place them against each other and then look at them through a 2 cm wide slit. Now move one comb a bit to the side. While looking through the slit, it's very difficult to figure out if you are off to the left or to the right, and by how many notches. It's the same for the AF system.

Thanks so much for tsking the time to post this. As one of the most experienced technical people on here - hearing from you I dont have a problem is very Reassuring.
Especially as this lens works brilliantly in all other respects, I was confused.

My theory on the problem was based on some advice I had from a good Landscape Tog, who said if you get Moire, either change the focal length a bit, or slightly change the angle of shooting. He said only a little change can stop it.

I wondered if you knew, if say my lens is on the loose side as appossed to the tight side, can Canon slightly adjust it, or is it all down to the bayonet fitting? ( i.e. Need a new bayonet fitting ).

Some radial play is necessary for the bayonet lock to be able to engage. Getting rid of it would render your lens useless. It has no effect whatsoever on the performance of your lens/camera combination, as long as it stays within the limits you described. You can get a feeling for the tolerance by looking at the size of the contact pads at the rear of the lens. As long as they hit their corresponding contact pin in the camera, you're fine.

apersson850 wrote in post #17434034
Some radial play is necessary for the bayonet lock to be able to engage. Getting rid of it would render your lens useless. It has no effect whatsoever on the performance of your lens/camera combination, as long as it stays within the limits you described. You can get a feeling for the tolerance by looking at the size of the contact pads at the rear of the lens. As long as they hit their corresponding contact pin in the camera, you're fine.

Thanks, oh they definitely allow the pin to hit the pad at all times. At worst my guess is the rotational play when locked would be less than a 1/20 of the width of a pin on the camera, maybe 1/40 th as its just discernable. And the pads on the lens are a lot wider than the pins on the camera.

I suppose my only corncern is its ever so slightly looser, locking down ( i.e. Pulling body to lens -,but that could be even down to the fact that the 70-200 L stays on the body permenenently and could have flattened the black weather seal a little) than the 70-300L.

Submariner wrote in post #17433095
Is this normal or should it lock to an immovable position i.e. No rotational play whatsoever.?
Is your 70-200 L F2.8 II wobble free for the whole lock up twist, or is it like mine just wobble free for the last 1/2 of the twist?

for most of my bodies, and all the lenses mountable to the tripod via ring instead of the camera body, i have some play both rotational and up/down/side when the ball head is semi-tightened down and i am moving the camera around by grabbing the body.

they're all like that in my experience if you yank hard enough.

but... you'd have to put at least some effort into it. the lens doesn't wiggle or anything unless you use some force.

Xyclopx wrote in post #17436497
for most of my bodies, and all the lenses mountable to the tripod via ring instead of the camera body, i have some play both rotational and up/down/side when the ball head is semi-tightened down and i am moving the camera around by grabbing the body.

they're all like that in my experience if you yank hard enough.

but... you'd have to put at least some effort into it. the lens doesn't wiggle or anything unless you use some force.

Thanks very reassuring, must say I have not had the nerve to pull either the lens or body around any more than uber gently.
My concern was just the difference in stiffness locking the lens on the body with the 3 lenses.

Once upon a time Canon had a breech-lock system, where you compensated any play introduced by wear and tear by simply tightening a bit more. But they gave that up on the introduction of the EF/EOS system. Besides, systems with electrical contacts actually benefit from the pins dragging over the electrical contacts when the lenses are mounted, as that clears away oxidation.

apersson850 wrote in post #17437249
Once upon a time Canon had a breech-lock system, where you compensated any play introduced by wear and tear by simply tightening a bit more. But they gave that up on the introduction of the EF/EOS system. Besides, systems with electrical contacts actually benefit from the pins dragging over the electrical contacts when the lenses are mounted, as that clears away oxidation.

So does that mean I can't have it tightened up if it needs it? ( on the 70-200 F2.8 L II ) . As the other 2 lenses are tight enough IMO, I assume its not the 5D3 body.

I may go down to CPS and ask them if this is within toelerance. If it is not, Imgues theynwould have to replace the bayonet part - I suppose that would be expensive?

Just out of interest is it better to take off the lens after the shoot?
I always leave it on to minimise dust getting in.

I always leave lenses on. Everytime you put in or take off a lens is when microscopic wear happens in the mounts. Post a video of your loose mount so we can see how bad the play is. I would say that play is generally bad. Play will lead to more play.