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How to ensure my Nikon D7000 does not having back-focus...

km6xz

St Petersburg, RU
3559 posts

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"RE: How to ensure my Nikon D7000 does not having back-focus issue"

km6xz Moderator Awarded for his in-depth knowledge in various areas, including Portraits and Urban Photography Nikonian since 22nd Jan 2009
Sat 16-Feb-13 06:33 AM

As others have suggested, the focus target in both these cases are difficult for AF to figure out what you intended. The sand because of lack of contrast or edges and the first one with the highly complex subject with many focal planes in the same focus point. The problem you have may be real or not, these images are not going to demonstrate a problem however. If, for example, you had targeted the flies in the second image, because they present distinct edges and contrast separate from the indistinct low contrast sand, the test would have been a better illustration of focusing accuracy.
A focusing chart, at the recommended distances, with strong uniform light would be the best way to see if there is a problem. Since you mention that other subjects or times, focusing is what you intended. Do you have an example you could post so we can see one? If there was a AF miss-calibration, I would guess that all images would be biased to the wrong focal plane.
The reason many people assume AF is not working correctly is because AF guessing your intent, it really does not know what is your intended subject and if there is any ambiguity in focal planes falling under the focus point, a guess could deliver a well focused subject, but not your intended subject. AF has become so good in recent years, most of us assume that when an image is off, that there is a problem, when in fact, the surprising thing is how often the system guesses the same focal plane we wish for.
Your camera might have a problem or might not, tests that isolate the AF system as much as possible as the variable are needed to find out.
The variables needed to remove from the test include:
Camera motion so a tripod is needed.
Target ambiguity, so a parallel flat focusing target is needed
Edge contrast, using a recommended test pattern target
Light fluctuation, meaning using continuous strong lighting, not florescent which varies greatly in intensity and color during each cycles of the mains line frequency.
Broadspectrum light, so that shift of focus plane is not a problem when testing wide aperture lenses. Different wave lengths of light are diffracted differently by the lens glass
Mirror bounce, use mirror up and a relatively fast shutter speed to negate the vibration that the mirror bounce generates and can induce image blur.
Camera steadiness, so use the ML-3 wireless remote, timer or wired remote so your button press does not shake the camera.
Focus target needs to be a recommended distance from the camera, the distance depends on the chart itself so follow the instructions for any particular chart.
Random fluctuation in focusing, by taking a series of shots and place the greatest weight on the focusing plane that the most images in the test represent.
Lens hysteresis, between each shot, set the focus to infinity so the AF has to approach and stop at the focal plane.
The balance this effect, repeat the tests but where each shot is begun with the focus is set to minimum. Compare the two sets.
Reference image, take one shot with Live View which uses an entirely different method of focus target selection, and one where you tell it precisely what focal plane you want. Under these test conditions, Live View should be more consistent and reflect the ultimate capability of the camera, lens and AF system.
All the items mentioned above are highly variable in our hand held shots so while some complain of occasional missed focus, some of us marvel at how many of these compromise conditions are overcome to produce as many sharply focused images of our intended targets the AF delivers. When dealing with complex targets and having a specific artistic focus point in mind, many of us who grew up on manual focus, switch to MF and control it ourselves. You always get the focus plane you set in MF, but you might not get the optimum focus plane because we missed ourselves. The owner's manual for the D7000 has an excellent list of good and poor AF target types. Feeding the AF system with good AF target types really increases the number of results where the resulting images match or expectations.
Good luck, but mostly, have fun!
Stan
St Petersburg Russia

Visit my Nikonians gallery.

A general, generic topic How to ensure my Nikon D7000 does not having back-focus... [View all] , technicalganesh , Tue 12-Feb-13 02:43 PM
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