Panasonic 20mm f/1.7 Auto Focus

Started Feb 14, 2013 | Discussions thread
micksh6
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Re: Lots of talk about AF times but what about some measurements (part II)
In reply to Anders W, Mar 17, 2013

Anders W wrote:

Conclusion: It is easily seen that the differences between tests as well as lenses are generally so small as to not be of much significance for most practical purposes. The shortest average recorded is 0.33 s (the 20/1.7 on test 1) and the longest 0.49 s (the 12/2 on test 2) but not too much can or should be made of this or other differences. As I pointed out, AF times may vary somewhat from one try to the next even if circumstances remain unchanged and if I had made more than five trials per lens and test, the exact times reported may well have been slightly different. The reason that I didn't extend the test to 50 trials instead of five is simply that the level of precision is already sufficient to prove the major point (not much of a difference) and that it is a quite time-consuming and boring task to play back videos one frame at a time and count the number of frames between certain critical events.

In essence, the results are the same as those obtained by Pekka Potka in this earlier comparison of the AF performance of the Olympus E-P3 versus the Olympus E-P2. While Potka's times are significantly longer than those I report, that's primarily because they include the time required for aiming the camera and actually firing it rather than the time required by the AF process alone. The important common denominator between his results and mine is that there is little difference between the AF performance of various lenses but considerable difference between the AF performance of older versus more recent bodies.



Anders, since you will probably refer to this post in future, I'll leave my note for those who read responses.
Your test doesn't represent real life because

  • Focus target is too contrasty. Often we don't have such luxury in real shooting. As I showed in my tests focusing speed/hunting greatly depends on target. And I won't accept an advise to choose another target because sometimes there is only one target, and other lenses don't require that.
  • Refocusing on the same target is too easy exercise for camera/lens.
  • Refocusing from infinity (especially from lens reset state) is different from what we do in real life. There is no infinity indoors.

Here is another set of tests that uses more realistic focus targets and it also shows how 20mm lens hunts like a dog:
http://forums.dpreview.com/forums/post/51100254
Overall, Pana 20mm is a great lens, it's sharp and it can take great pictures. Its focusing time isn't awful, it can be good enough for many people. But, the claim that 20mm focuses as fast as other fast primes is just plain wrong and it can mislead people.

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