D850 and 3D tracking AF

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Leonard Shepherd
Leonard Shepherd Forum Pro • Posts: 13,250
D850 and 3D tracking AF
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The test team says https://www.dpreview.com/reviews/nikon-d850-first-impressions-review/8 "we were surprised to find some issues with the D850's 3D tracking when the cyclist was weaving from side to side".

Nikon's 3D tracking is partly dependent on the colours surrounding the initial AF point. This applies to all models which have it, not just the D850.

The bottom of page 102 of the UK D850 User's Manual includes the same highlighted caution as for other Nikon bodies

"3D-Tracking

When the shutter release button is pressed halfway, the colours in the area surrounding the focus point are stored in the camera.

Consequently 3D-tracking may not produce the desired results with subjects that are similar in colour to the background or that occupy a very small area of the frame".

The street is mainly in shadow, the cyclist is back-lit by what light there is, the cyclist has a well tanned skin, black rimmed eye-glasses, his eye sockets are in deep shadow and his hair is close to black as is his "in fashion" unshaven face.

Contrast on his face is probably too low for AF of 2 decades ago to detect at all; colour tone differentiation is very low, and contrast with the background varies from very low in similar shade to a small sunlit area.

The cyclists face occupies a small area of the frame.

This brings up the question of whether the D850 3D-tracking has some issue only in lighting similar to that outlined in the Nikon User Manual caution as likely to be a problem, or if there is an issue in any lighting where there is reasonable colour differentiation surrounding the initial focus point.

I presume it would be easy for the test team to repeat this test sequence with the street in sunlight and a cyclist wearing perhaps a very different coloured helmet to his/her face.

This should clarify whether "some problems" apply to any lighting situation, or as Nikon indicate in their Manual caution, only where there is a lack of colour differentiation surrounding the AF point or the subject is small in the frame.

On a detail there is a school of thought that considers that 3D-tracking is best for subjects moving from side to side as in a tennis match, and that Auto AF is better when a subject is both weaving and coming toward the camera as in the test sequence.

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Leonard Shepherd
Some say if some of your photos are not good the camera you use is only a recording device.

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