70-200 f2.8 AF problem

[mish757]

Have a canon 70-200 f2.8 non IS lens that is having AF issues.  My other zoom lens (24-70 f2.8) is not having any issues paired with my 5D Mk III body, so pretty sure it is an issue with the 70-200.  The problem is with the AF on closer subjects (approx. within 25 ft) - on more distant subjects, the AF is tack sharp, but when I try to focus on a closer subject, the AF won't lock.  The motor continues to hunt for proper focus.  Tried cleaning the contacts, but still have the problem.  Anyone else have experience with this issue.  Thought I would ask you experts before shipping the lens off for repairs.

[ebiggs1]

Still think it might be the camera. 

Whenever a camera seems to be doing something strange (or not doing what it should) it's worth a try to use the 'restore all settings to factory' option.  The lens doesn't know when it is in focus.  The camera does.  You may have a C.Function set incorrectly.

Besides that it could be you.  The scene you are trying to shoot.  No contrast, too dark, too close, etc, for instance.

[RobertTheFat]

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@ebiggs1 wrote:

Still think it might be the camera. 

Whenever a camera seems to be doing something strange (or not doing what it should) it's worth a try to use the 'restore all settings to factory' option.  The lens doesn't know when it is in focus.  The camera does.  You may have a C.Function set incorrectly.

Besides that it could be you.  The scene you are trying to shoot.  No contrast, too dark, too close, etc, for instance.

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And I still think it might be cured with AFMA (assuming that the camera isn't a Rebel). The nice thing about AFMA is that it doesn't matter whether the problem is in the camera or the lens. It treats the symptom, not the disease.

[kvbarkley]

Except the problem is not that the focus is off, it just can't focus, it hunts.

It looks to me that for some reason there is a lot of play in the AF connection to the focusing elements at 25 ft distances.

[mish757]

You guys have way more knowledge about this stuff than I do.  What is AFMA?  And when you say "a lot of play in the AF connection to the focusing elements", is that something in the lens itself?  Moot points since the lens is in the mail to the Canon repair facility...just curious.

[TTMartin]

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@mish757 wrote:

You guys have way more knowledge about this stuff than I do.  What is AFMA?  And when you say "a lot of play in the AF connection to the focusing elements", is that something in the lens itself?  Moot points since the lens is in the mail to the Canon repair facility...just curious.

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AFMA is used when a lens is focusing, but, either front or back focusing instead of accurately focusing. Since your lens was having difficulty focusing at all, I doubt AFMA would have fixed your issue.

[mish757]

Thanks, TT.  I think you're right.  It's not that it was focusing and the image was coming out blurry, it wouldn't focus at all on the closer subjects.  When it focussed on a more distant subject, the image was sharp.

[RobertTheFat]

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@mish757 wrote:

You guys have way more knowledge about this stuff than I do.  What is AFMA?  And when you say "a lot of play in the AF connection to the focusing elements", is that something in the lens itself?  Moot points since the lens is in the mail to the Canon repair facility...just curious.

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We're just thinking out loud. You're doing what we'd probably do if we were in your shoes.

AFMA is "autofocus microadjustment". It's a method of calibrating the accuracy of the AF mechanism. Most higher-level Canon cameras have it. The Rebels don't. If your camera has it, it's described in the instruction manual.

[ebiggs1]

Robert from B Town, it ain't AFMA.  It might be a C. Func., though.

[TCampbell]

It sounds like your lens needs service.

If you focus the lens manually, is the focus able to move freely from closest focus to infinity?

Note that "L" series lenses with USM focus have a clutch which allows the focus mechanism to slip against the rotation of the focus ring on the lens barrel.  So you'd probably want to look through the lens or watch the focus distance scale in the window move as you rotate the focus ring.  

You're looking to see if it has the full range of focus range without sticking or jamming.

[Waddizzle]

Two questions:

!.  Are you able to focus the lens manually at those ranges?

2.  If you have a filter on your lens, remove it.  That's one less question mark in the problem.