AF speed D700 slower than D3? how come ?

Started Aug 7, 2009 | Discussions thread
Steve Bingham
Steve Bingham Forum Pro • Posts: 25,453
Re: You're on the right track

Marianne Oelund wrote:

Steve Bingham wrote:

em_dee_aitch wrote:

Again, this is huge. If you think the D700 is as good, you're kidding yourself.

Maybe. Maybe not. Consider the test variables:

1- The first test was done by Michael McNamara (the same guy who picked my digital photos to be the first published by Popular Photography - along with Eric Meola, December 1994, Digital Comes of Age). Michael's test was done in Jan 23, 2008. The second test was done by Philip Ryan - using a DIFFERENT lens. Michael left Pop Photo before the 2nd test.

Correct. Changing the lens (or even the focal length) invalidates the comparison.

2- The first test was done at ISO 100. The second test at ISO 160.

I'm not terribly bothered about this, due to the separation between AF and image processing.

3- While the focusing test read .29, .31, .38 seconds for the first three light levels with the D3 the D700 test recorded .35, .36, .36. depending on light levels. We are talking thousandths of a second. This variable is well within different lens samples of the same lens.

Variability is a fact of life with AF, and studying it accurately requires a statistical approach. You can't simply sit down, take a few measurements and consider the job finished. A proper investigation takes considerable patience, and I absolutely do not consider the differences between numbers quoted above to be proof of anything.

In short, you really can't take these times to be exact unless the variables were better controlled. In actual use, I could never detect the difference of 6 thousandths of a second focusing speed, much less 4 thousanths, or even 2 thousandths better in the case of the 3rd light level.

Well, they're hundredths, not thousandths, but your point is still valid.

I know better! Yikes. Thanks for pointing this out. Typing faster than my brain was thinking. I blame it on old age! :^)

The numbers can vary wildly from run to run, and this is why we see people making outrageous claims from field use experience, such as "camera A is only 30-60% as fast as camera B" when they may actually be very close.

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