Friday, March 12, 2010

Peculiar AF Issue

This post is a place where I can refer people to about a really bizarre auto focusing issue that I’ve been having, without having to repeat it over and over again.

Introduction


I’ve been using D70 for over 5 years and I’ve taken about 50,000 shots. I’ve had D700 for 2 weeks before I exchanged it for the pricing reason1, and B&H shipped the same camera back to me and I haven’t noticed an issue. I first noticed the problem on the day that I received this camera and a lens for the 2nd time.

The Issue


In short I believe there is an AF problem that happens in very specific conditions. It also seems to me that this must be a defect with the camera, the lens, or both. It happened so that my test subject of choice was a sticker on a Peach Snapple bottle that was on my desk. This, in fact is the one and only item that I can replicate the issue on.

Peach Snapple.This is my test subject. The photo is taken when everything worked without a problem.

Specifics


Here’s a way to trigger the problem. These are the steps that I’ve been taking to consistently reproduce the issue.
  • Camera is set to single servo, single point focusing. Central point is used.
  • Focus on a word “black” in the center of the sticker by half-pressing the shutter release button or by pressing AF-ON button. Keep the distance between the camera and the bottle as small as possible. Camera achieves good focus and indicates this by lighting up a green circle in the view-finder and beep sound.
  • Refocus the camera at an object at infinity — something outside the windows worked for me.
  • Point the camera back to the bottle and engage the AF again. Camera attempts to adjust the distance on the lens and reports a focus lock by the use of the green circle and a beep. However the object is widely out of a focus.

Peach Snapple. Ouf of focus.This is a resulting shot. Everything is out of focus. But even looking like this you’ve got to give the credit to the Nikkor lens for making it look pleasing anyhow.

Another way to reproduce the issue. Basically the idea and the concept is exactly the same as above.
  • Focus on the sticker and achieve good focus and focus lock by pressing AF-ON button and release the button.
  • Spin the manual focus ring on the lens all the way to infinity.
  • Engage the AF function by hitting AF-ON again. The camera thinks that it locked on by displaying a green circle and beeping, yet everything is way out of focus.

The Bizarre Part


Naturally my next step was to test the camera and the lens in different combination. I’ve done the following test with the same exact result — false positive on focus lock.
  • D700 + Nikkor 24-70mm
  • D70 + Nikkor 24-70mm
  • D70 + Nikkor 18-70mm
  • D700 + Nikkor 50mm

This might suggest that this is normal behavior, but I find that hard to believe. My mistake was not testing D70 with 18-70mm lens first. Now I have no way of knowing if it in fact did behave this way all this time, or if the lens caused it to malfunction. I also don’t want to test with any Sigma lenses at this point as I’m not sure how it’s affecting the bodies and the lenses. If I were told about this by somebody else I would classify them as insane, yet this what I’ve experienced and I have no explanation for any of this.

Clarifications


Do note that I’m not talking about the camera being unable to focus — that can be caused by many different things — lack of light, being too close to the object, etc. The issue is the fact that it does think that it focused, as indicated by the green circle in the viewfinder and a beep sound. I also have camera set on focus priority in AF-S, meaning that the camera would prevent me from taking a shot that it didn’t focus on.

Looking For Help


I’ve tried posting on various forums with no good results. I contacted Nikon support and so far haven’t heard a word back from them, even though I was promised an answer back on Tuesday. I’ve contacted B&H tech support and they were puzzled as much as I am.

At this point what would be really helpful is someone with a Nikon body and a lens performing a number of these tests on the same type of Peach Snapple bottle and trying to replicate the issue.

Conclusion


I myself am planning on going to B&H as soon as I’m able and asking to test a different copy of D700 with 24-70mm lens. Also I’m hoping that if this is not a normal behavior they will not have a problem exchanging my equipment.

In all other respects camera performs exceptionally well. I was not able to cause it to miss focus in any other way, but again, I want to get to the bottom of this problem and establish if it’s a common behavior, I’m doing something silly or I have a faulty combo. It’s not a cheap toy to just let this go.

Focus test chart.I also performed a normal focusing test on the lens and the results are very good. Note that focus line might not fall exactly where it should because I’ve misaligned the test chart slightly while taking photos.

Update


Went to B&H today. As was recommended to me I spoke with a guy named Gerry who worked with Nikons for many years.

He hasn’t seen a thing like this before, but he spent about 30 minutes listening to me and working on the issue with me. Eventually he brought over another body and a lens (same combo) and we easily replicated the problem.

So this is the conclusion. All Nikon (didn’t test the others) bodies seem to do it. Some choice of a test subject I had, eh?

I’m satisfied to know that my copy is perfectly fine. Huge props to B&H yet again for superior customer service.

  1. Nikon started a rebate program 2 weeks after my order that would save me $300 when I buy the camera and the lens that I bought as a kit instead of as separate items. B&H had no issue closing out the first order and creating a new one so I would qualify. They didn’t have to do it, but they made this customer very happy. []
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