Serial numbers
My D800E has a serial number of 3001xxx and it was a first week release. A similar range of serial numbers included some D800 models. Nikon does not repeat serial numbers, so there must have been some type of coordination of serial numbers during production. My understanding is the D800E is created by modifying D800 cameras but I don't know anything about the stage in assembly.

AF testing
There are lots of things that can be tested on the camera. The center sensor should be the most accurate for focus and is used for testing and fine tuning AF for your lens. If your lens is not correct, other results may not be accurate.

Using the center sensor for AF, you can test for sharpness of your lens across the frame. Most lenses are less sharp as you move to the edges. so it gives you a baseline.

Live View uses a different technology for testing that is generally more accurate. With the center sensor, you can use Live View to compare the two methods of AF and assess whether the Phase Detect system of regular viewfinder focus is accurate. Keep in mind that both Phase Detect (regular focus)and Contrast Detect (Live View focus) AF have variation so there will probably be some test images from PD that are as sharp or sharper than CD.

Focus accuracy testing is normally done at the widest aperture and a medium focal length - 35-85mm. The shallow DOF of a wide aperture makes it easier to see focus accuracy or errors. Stopped down the increased DOF makes many focus errors hard to see. Keep in mind that wide open is not the sharpest aperture - it is simply for testing.

When you are testing you should defocus the lens slightly. If you defocus the lens to an extreme, you'll get a lot more errors and that's not the point.

The left focus issue is a problem with the far left center focus point. We know that outer AF sensors are less accurate than the center sensor, but in this case if you have a problem there is a distinct focus error on all frames. By taking a set of test images using the far left AF sensor and Live View, you establish a baseline for what kind of sharpness is possible using CD focus. Then you create a set of test images using the far left sensor and the shutter or AF-On button (your choice depending on how you activate focus). If the Live View images are sharp, and the PD images are all out of focus. You would test the far left, center, far right sensors and any others desired.

There is a lot of discussion about focus targets and the distance of those targets. You want to set up your target at a relatively close distance - 4-5 feet for a 50mm lens. This lets you see enough detail that you can see focus errors. You can also test at normal shooting distance, but that may produce different results at different distances. For Fine Tuning focus for each lens, you will vary the distance from the target with the focal length.

It is extremely important that your camera be perfectly square to the target. Some systems use a mirror on your target to make sure alignment is perfect.

There are a lot of possible test targets. The key is the target needs to be flat with strong, bold lines that make focus easy. Angled rulers are used for scale to show the direction of the error - not for focus. The target needs to be well lit. A tripod and cable release should be used for testing. You also want to use AF-S and single point auto focus.

I would not spend a lot of time doing real testing until you have some indication of a problem. Just take some images using the center sensor and make sure they are pretty sharp. Then take some images using other sensors and see if there is any pattern that all the images are out of focus. If the images are okay using the extreme focus points, you're fine. If you have a question, then you can get into further testing.

Eric Bowles
Nikonians Team
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