[dosdan]

Why AF.C paired with a manual focusing lens?

I used a MF lens because I didn't want the speed altered by waiting for focus. Although, with AF the delay should be before the burst starts and hopefully there will not be any further delays during the burst while AF updates. The initial AF delay is not considered here. We're not including the time from when you hold down the shutter release button until the end of the burst, because the initial delay is variable and will change with lens and situation. So I time from peak to peak (the loudest part of the shutter movement - there's a number of peaks).

Normally, I would not use a MF lens with AF.C, but use it here to reduce a variable: any further AF update delay during the burst. If the target is static (I performed the test on a tripod) AF performance should not affect the burst speed once it starts (which is what I'm measuring).

Dan

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Last edited by dosdan; 10-23-2011 at 12:16 AM.

[dosdan]

Here's another way of determining the burst speed that should be easier for users. It was suggested by Schmegg in the forums.whirlpool.net.au Photography forum: Photograph a stopwatch program on your PC e.g.

Free stopwatch and countdown timer

Here's how to use this method. It's not as accurate as digital audio (PC timers can be a bit unreliable), but probably good enough for this purpose..

1. Install the timer display program and start it running showing seconds to at least 1 decimal point.
2. Photograph the timer display in a burst until the buffer fills (I suggest a tripod to prevent AF adjusting during the burst (at the start is not a problem).
3. Say the first shot shows the timer (in mm:ss.ddd) at 10:25.100 and the 24th shot shows 10:28:642. The difference is 3.542s over 23 shots (take away 1 for the start). So the burst rate is 3.542/23 = 154ms/shot and 1s/0.154ms = 6.5 fps
4. To ensure that no unexpected stutters occurred, I'd suggest also checking about half-way from the start too. So in this example, at the 13th shot and divide the difference from the first shot by 12. The result should be close to the full burst speed.
5. Send the fps and the other requested camera info to me.

Dan.

[dosdan]

Some new test results. I put on a AF lens (Sigma 17-70/F2.8-4.5) and compared AF.S vs AF.C. I think you'd be more likely to use AF.C for continuous bursts in action shooting. I also compared Centre-point and Auto focus-point selection. These tests were repeated a number of times and 2 different Class 10 cards tried.

Results with Centre-point focus are:

AF.S 6.8 fps
AF.C 4.8 fps

with Auto-focus point selection approx 0.1 fps slower.

Burst length was usually 20 (AF.S) & 22 shots (AF.C).

The AF.C performance is still considerably better than my K20D which was only about 2.7-2.9 fps.

Dan.

[RonHendriks1966]

Results with Centre-point focus are:

AF.S 6.8 fps
AF.C 4.8 fps

with Auto-focus point selection approx 0.1 fps slower.

Not so bad. I think in the field with a reallife sport it is not so fast as you messured. To my feelings it gets down to just over 3 fps, but when your scene doesn't change to much at a time it does a quicker series of shots and probably gets to those 4.8 fps.