Please help me to verify - Left AF Problem or lack there of

Started Apr 20, 2013 | Discussions thread
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Marc Heijligers Contributing Member • Posts: 526
Re: Please help me to verify - Left AF Problem or lack there of

Leonard Shepherd wrote:

There seems a very slight loss of quality on image 2.

Why use a geometric pattern as a target when Nikon warn you they may cause poor results?

What Nikon tries to say is geometric from the viewpoint of the AF sensor. If you average the images in horizontal direction, which is what the AF sensor (roughly) sees, both pictures (centre first, left next) look as follows:

Centre

Left

Hence, to the AF sensor, these pictures are not geometrical at all. It shows that a displacement results in two different scenes for the AF sensor, but both have sufficient vertical detail to reach acceptable focus results.

If you look into the patents, you see that Nikon also applies contrast enhancement to increase the level of vertical detail. I don't know their exact algorithms, but if you tighten the histogram, it looks as follows for both:

Centre

Left

I.e., in practice this target should give good focus results, at least good enough to see if you have focus issues.

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