I feel misled: Panasonic 20mm f1.7 II AF is SO SLOW!

Started Apr 28, 2014 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: I feel misled: Panasonic 20mm f1.7 II AF is SO SLOW!

micksh6 wrote:

Anders W wrote:

micksh6 wrote:

Anders W wrote:

micksh6 wrote:

Why do you feel mislead? Of course it's slow and it has been shown here long time ago. You just needed to look at the right tests:

A "controlled" test can also show that 20mm focuses much slower than other lenses and hunts more often too. It's not needed to refocus from close-up to infinity in order to see that. These tests show refocusing between about 5 and 7-8 feet.

Those tests are not controlled. They are biased in ways and for reasons spelled out in the thread to which you link. That's why they are not the right tests.

I didn't start this thread stating that 20mm is slow, so you might as well tell OP that he is biased and the lens is actually fast.

Don't worry. I already told him what the facts are a couple of times, latest here:


Whether you like my tests or not they showed exactly what OP is seing now. Your tests, on the other hand, showed that 20mm is as fast as other lenses.

My tests show exactly that yes, but only under the specific conditions I spelled out in the post where I originally reported my test results as well as in posts where I refer to them, latest in the post I link to above. As you you should be well aware by now, I have no trouble recognizing that the AF of the 20 is slower than that of other lenses under several other conditions. As you can see, this too is clearly pointed out in the post I link to.

The problem with your tests is that they don't show much at all due to unrobust test conditions that make the outcome very sensitive to minor variations along with a failure to control these variations sufficiently well.

BTW, a year ago I replied to your post with test results which you linked today: "the claim that 20mm focuses as fast as other fast primes is just plain wrong and it can mislead people". http://www.dpreview.com/forums/post/51100467

Perhaps, this is why OP feels misled now.

So you erected a straw-man. The unconditional claim made in the passage of yours that you quote is not and was not my claim. What I am, and have been, claiming is summarized in the post I link to above.

What I said is exactly what you have been saying for a long time

"The practically relevant test data are here and show the 20/1.7 to be just as fast as other, more recent lenses, in ordinary AF-S, even when refocusing within as extreme a span as infinity to 75 cm."

Many thanks for choosing such an excellent example of your straw-man tactics. The passage of mine that you quote includes two conditons (ordinary AF-S and refocusing within the 75 cm to infinity range) that you omitted. The third condition that I mention in the post I linked you to above (no hunting) was not at issue in the exchange with Fredrik G. from which you picked the quoted passage so I found no reason to mention that in my reply to him.

Other your explanations just make your point more clear

"Reason: In virtually all cases, the bottle-neck is body processing time, not the lens AF mechanism."

Taken from here: http://www.dpreview.com/forums/post/52375461

This is just one example, I could find dozens of such examples from the last couple of years where you claim that 20mm AF is as fast as other lenses AF.

There was never a disclaimer about shooting conditions. You made dozens of such unconditional claims in almost every thread related to 20mm lens AF.

See above for the perfect example to the contrary that you provided.

Now where are your answers to the questions I asked?

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