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Author Topic: Is the Nikon 51-pt AF system actually capable of f/8??  (Read 1539 times)

jrista

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Is the Nikon 51-pt AF system actually capable of f/8??
« on: March 31, 2012, 06:10:03 PM »
While digging around the bowls of the internet looking for solid information on Canon and Nikon AF systems, I came across Nikons own official page on their 51-pt AF system. I found the following blurb (from http://www.nikonusa.com/Learn-And-Explore/Nikon-Camera-Technology/ftlzi4pn/1/51-Point-Autofocus-System.html):

Quote from: Nikon
With the new Nikon D4, the AF maintains the power of the five cross-type sensors in the center as long as the combined open aperture value is below f/8.

I've emphasized the most important part. The Nikon 51-pt AF system works with the five cross-type sensors in the center as long as the maximum aperture is BELOW f/8? Where exactly does Nikon say their AF system supports f/8 autofocus? Where exactly is the information that declares the D800 or even D4 capable of even center-point AF with a maximum aperture of f/8?

For all the hullabaloo about how the 5D III and 1D X are inferior to the Nikon offerings...I'm not sure there is actually any evidence to support the idea that Nikon cameras can AF AT f/8. That would at best put them on par with Canon's new AF, and they are certainly trailing behind in the area of higher-precision cross-type points (15 with Nikon's 51pt AF system, vs. 41 with Canon's 61pt AF system.)

So...where exactly is f/8 AF for Nikon?
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Is the Nikon 51-pt AF system actually capable of f/8??
« on: March 31, 2012, 06:10:03 PM »

neuroanatomist

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Re: Is the Nikon 51-pt AF system actually capable of f/8??
« Reply #1 on: March 31, 2012, 07:14:27 PM »
From the D4 overview page on the Nikon website:

AF detection up to f/8
D4 aligns its 15 cross-type sensors in the center to detect contrast for both vertical and horizontal lines with lenses f/5.6 or faster. The five central points and three points to the left and right of them in the middle line are compatible with f/8
.

So, 11 points at f/8 and 15 points between f/5.6 and f/8. It's unstated, but it might be that at f/8, they aren't cross-type (but I recall reading somewhere that they are).



« Last Edit: March 31, 2012, 07:23:23 PM by neuroanatomist »
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Re: Is the Nikon 51-pt AF system actually capable of f/8??
« Reply #2 on: March 31, 2012, 07:22:02 PM »
Unfortunately marketers didn't learn much maths in high-school.
To me, there's a big difference between <f/8 and =<f/8, but to them, as long as they've got an 'f/8' on the page it's good enough...
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Re: Is the Nikon 51-pt AF system actually capable of f/8??
« Reply #3 on: March 31, 2012, 07:32:15 PM »
Unfortunately marketers didn't learn much maths in high-school.

... but reading "AF detection up to f/8" as "not including f/8" would be just misleading and only worthy of Canon marketing :-)

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Re: Is the Nikon 51-pt AF system actually capable of f/8??
« Reply #3 on: March 31, 2012, 07:32:15 PM »