5d Mark III AF issues... need help!

[pbfmini]

I bought this camera in march of this year and its never missed a shot. One week ago I noticed it was not focusing properly. I was in an indoor arena practicing low light so I didnt think anything of it. I have been adjusting settings all week now and CANNOT get it to focus properly.  Even resetting it to original settings did nothing for it.  I use a 70-200 f 2.8L almost always, however, last friday I experimented with both a 50mm and external flash.  I have a 2 day horse show to do this weekend, I need this this to work! has anyone experienced this or have any insight? TIA

[ebiggs1]

"I think that's a bit of an oversimplification."

That is exactly what he needs right now.  You can't run before you can walk.

[pbfmini]

update! it was the 70-200mm lens that was off, not the camera! sent it back to canon and just heard back from them today. Thank you all for answering my panicked questions and sorry i never responded- i work a lot 😕 Looking forward to getting my gear back and very thankful for all the nice, helpful replies!

[cale_kat]

"....  CANNOT get it to focus properly."  Is it focusing at all? You suggest that it might not be focusing at all but the word "properly" means that it might be focusing but not the way expected or desired.

So, could you clarify that the lenses are set to AF? Could you tell us if it focuses at all? And if so, is it hunting for focus? Is it tracking? What isn't it doing? Details, please.

[TCampbell]

If it isn't doing what you want it to do, it's extremely beneficial to pinpoint exactly what it is doing.

To this end, you'll need to do some proper focus tests.  Real-world subjects are lousy for this because you cannot take specific measurements.  It's much better to use a test target.

I have a commercially made target (e.g. Datacolor "Sypder LensCal" or a "LensAlign").  But you can also get a test target that you can download and print from the Internet... such as this one:   http://regex.info/blog/photo-tech/focus-chart

The idea behind these is that you'll careful test conditions to isolate any other reason for the camera not focusing accurately.

Mount your camera on a tripod and now you know that the lens isn't moving and the camera isn't moving (so there's no blaming the photographer for not being steady).  

Place the test target at the prescribed distance (follow the instructions that come with the chart.  The distance will depend on the focal length of the lens.)

Select the focus point you plan to test (e.g. center point focus).  CAREFULLY algin the camera so the focus point being tested is on the high-contrast test-target position.

Make sure the camera is using "One Shot" AF mode (not AI Servo -- use "One Shot" for stationary targets such as this one.)

I deliberately de-focus the lens in one direction ... for example manually turn the focus ring to minimum focus distance.  There are two reasons for this... (a) I want to make sure the camera MUST adjust focus on each and every test) and (b) I want to know the direction that the camera had to move focus in order to achieve focus (e.g. if it was set to minimum focus distance then the camera must move focus out.   If it was focused to "infinity" then I know the camera must move the focus in.

Take notes so you know where focus started and which direction it has to move focus.

And since 1 sample does not make a trend... you'll need to shoot at least a half-dozen shots for each direction of your test.

The chart is laying back at an angle.  This means if the camera is "front focusing" you'll notice the areas on the chart that are a bit closer have better focus than those at the intended target position.  If it's "back focusing" you'll see the opposite.

If the camera CONSISTNTLY misses focus (say it's always just slightly back-focusing) then you can adjust this using the camera's built-in auto-focus micro-adjustments (see your manual).  

If it is NOT CONSISTENT then you have a different problem and the lens may require service.

The focus mechanism is mechanical... glass and other parts are moving to focus.  Gears can develop backlash or "slop".  This means if you move focus in one direction, then reverse to move focus in the other direction... a certain amount of free travel could occur before the lens actually starts moving again.

The bottom line... using good testing conditions to figure out exactly what your lens is doing.  It also means that if you do decide to send the camera and body in to Canon then you can describe the issue more accurately.

For further reading:  http://www.lensrentals.com/blog/2008/12/this-lens-is-soft-and-other-myths