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:

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.

The "bias" reasons were spelled in regards to first test (more than a year old). This is why I linked to a second test (9 months old) with corrected conditions, so all that bias stuff is no longer relevant.

When you reviewed the second test you couldn't come up with any bias arguments, only with minor nitpicking about viewing angle. These nitpickings were pointless because anticipating these I did several tests with slightly different angles and they all showed the same results.

No they were at the same angle but with different framing of the target.

Here is your last post in that discussion: http://www.dpreview.com/forums/post/52056626


The test is as right as it could have been. Any more "controlled" test would also be less relevant because it would have to use artificial conditions, having nothing to do with real shooting.

Your test is a good example of irrelevant test because now you always have to add disclaimers like "when refocusing between 0.75m and infinity".

That disclaimer is not some kind of artifact of my testing. It describes the boundaries within which the 20/1.7 will focus about as fast as other lenses. I did another test before that where I had the minimum distance at 0.5 meter rather 0.75 meter. When refocusing from infinity to 0.5 meter, you start seeing a difference between the 20 and other lenses although not a very large one. When you go from the minimum focusing distance (0.2 m) to infinity or the reverse, the 20 takes about twice as long as other lenses.

Why didn't you test a real life scenario - refocusing between approximately 5 and 7 feet, like I did?

The reason why I chose 0.75 meter and infinity for one of my two test scenarios is explained above. I don't think there is any particular pair of distances that can be considered more real than others in this case. Why, for example, didn't you test refocusing on a target at the same distance as I did? Refocusing on the same target happens, I would think, quite frequently in real shooting.

Your ending word was basically that "If you want to make one lens look like it would be more prone to hunting than other lenses, it's very easy to arrange that by means of any of a large number of seemingly minor side conditions".

It could be so, and that's where statistics comes to play.

Rather, that's where confirmation bias comes into play.

More and more people find that 20mm is slow comparing to other lenses.

What do you know about that? I might as well say, based on a number of posts other than mine in this thread, that more and more people come to about the same conclusion as I. In reality, all we know is that perceptions are widely different.

Nobody appears and says that 20mm is faster than recent primes such as 17mm F1.8 (especially that 17mm), both 25mm, 45mm F1.8. Isn't that telling something?

Presumably nobody says so because nobody (myself included) thinks so.

The best what people can say about 20mm AF speed is "it's fast enough for me" or "about as fast as some other lenses I own".

Sure. And I have no trouble agreeing with either of those statements.

And this also should have raised "where's your evidence" questions that you ask everyone who claims that the lens is slow, if you weren't so attached to this lens, of course.

I don't need to ask others for evidence of something I have already shown myself.

Now what about the questions I asked you here:


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