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Some additional thoughts on AF

PAStime

Kingston, CA
2824 posts

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PAStime Silver Member Nikonian since 10th Feb 2009
Sat 09-Apr-11 12:00 PM | edited Sat 09-Apr-11 12:06 PM by PAStime

Hello,

This was a most interesting thread, lively at times and I certainly don't want to reopen the topic. But some of the articles referenced in the thread revealed some interesting aspects about AF that I hadn't appreciated:

- The tolerance range (variability and randomness of this variability) of successfully having achieved focus as determined by the AF module and the lens might be visible at 100% image viewing.

- The AF subsystem of some cameras work differently (enter into a higher precision mode such as use of additional AF points) when an f2.8 or faster lens is mounted on the camera.

- Wider aperture (faster) lenses transmit light at a wider set of angles to the AF module and this adds to accuracy and speed. Interestingly, image sensors prefer light at 90 degrees to the sensor surface as this increases efficiency/SNR/sensitivity.

- The AF function is inoperable during exposure (of course, because the mirror is up) but what's interesting is that means AF acquisition is disabled at times during rapid fire shooting. (Just an interesting engineering design challenge).

- The AF module in the D7000 contributes to many other things, including exposure, highlight analysis, white balance, and i-TTL flash control.

These are interesting tidbits to me as I'm always curious on how modern day cameras are engineered. What I don't know is how much of this applies to current day Nikon DSLR bodies.

Cheers,
Peter

My gallery (a work in progress): http://peterstokes.net/Exhibit

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