UPDATE: This is what a defective 7D auto focus system look like

Started Nov 3, 2009 | Discussions thread
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TomFL
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UPDATE: This is what a defective 7D auto focus system look like
Nov 3, 2009

For those of you who haven't tracked my focus problems, they are documented in a couple threads here:

http://forums.dpreview.com/forums/readflat.asp?forum=1019&thread=33525919

http://forums.dpreview.com/forums/readflat.asp?forum=1019&thread=33484504&page=1

Ultimately I decided to return the camera. I got a new 7D but also held on to the old one just for a test before I sent it back. I tested the new one against the old one this afternoon.

  • CONCLUSION: The old camera was defective, the new camera works much better.

My focusing on the old camera was erratic. Today I did some basic focus chart tests from two feet away and both cameras worked well. I also did several other tests, but ultimately after a while I found a simple and fast way to detect the problem with my unit:

FOCUS CONSISTENCY TEST

  • Aperture priority, Max aperture (smallest f number), tripod, auto ISO

  • Aim camera at an object (in this case it is a stucco wall 8 feet away).

  • Place your hand in front of the lens and focus (half press), this forces the camera to completely refocus on the object every time.

  • Remove your hand and refocus again on the object.

  • Note the exact location of mechanical distance indicator on your lens.

  • Repeat test and see if the camera focuses to the same exact distance every time.

My old camera could not do this consistently for the stucco wall target, it was visibly missing the mark about 1/3 of the time, sometimes badly. The new camera was spot on every time.

A few other details.

I also got a new lens, a EF 24-105 f4L IS, my old lens was a EF-S 17-55 f2.8 IS. I switched lenses between cameras and the old camera was still defective. However the new camera performed slightly better with the new lens. The mechanical rotation and start/stopping for focus seemed smoother and more fluid with the EF lens, the EF-S lens seemed to be "jerkier". It's a bit difficult to describe exactly. Maybe the EF just has better dampened motor control.

When the old camera would miss focus, it would focus short about 98% of the time.

I believe the old camera failed more often when the zoom was near minimum, when the zoom was extended, it failed less often. This may have been my imagination.

This test ID's the problem on my camera, your mileage may vary. The particular object being focused on during the test is important of course. Fortunately today I was able to immediately test another unit to see if it could handle a problem my old camera couldn't.

The new camera worked markedly better, but it wasn't perfect. There were occasional slight focus misses, but this was the exception.

The old camera would fail more often in 19 point focus mode, but it still occasionally failed in single point mode.

The new camera also could not focus on the ream of paper on the tile floor test in 19 point focus mode (see old thread). However it did consistently focus on the same spot, about 2 feet in front of the paper, where the old camera was not consistent.

19 point and zone focus do focus on the nearest object they can find most of the time with both cameras. The debate about what it does vs. what it should do vs. what is most useful is for another day. Nearest object includes the ground, which I think limits its usefulness.

Let's just say I understand how each focus mode works and how DOF plays a role much better than I did two weeks ago.

As has been mentioned repeatedly by others, use single point focus mode most of the time and reserve zone / 19 point focus for special conditions such as BIF or others.

Now I can take some picture instead of debugging the focus system.

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