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Pana 20/1.7 (version II) vs Oly 17/1.8?? Need help deciding.

Started Feb 24, 2014 | Discussions thread
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Anders W
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Re: slowness
In reply to micksh6, Feb 25, 2014

micksh6 wrote:

Anders W wrote:

http://www.dpreview.com/forums/post/51262836micksh6 wrote:

kenw wrote:

mh2000 wrote:

My nits against the 20 is that it produces starburst highlights (some like, I don't). It also tends to produce green polygon flare patterns (again, I don't like them). It can render things a little harsh.

Good point on the rendering - forgot to mention that. The rendering and bokeh are a bit different on the two lenses and that is very much a taste kind of thing. The 20 has more of an "energetic" bokeh that some find appealing and others a bit distracting. Really it probably more depends on the subject and composition as to whether it is desirable or not. The 17 is a smoother bokeh.

As to the speed I also perceive the difference you mention and the more failures to focus in low light than the 17. But as someone else linked Anders showed in some controlled conditions there isn't much of a difference. AF performance is a really hard thing to measure and also perceptions are sometimes different from reality too.

Of course there is a significant difference in controlled conditions. 17mm F1.8 is way faster than 20mm F1.7. 20mm F1.7 also tends to hunt in the same conditions where 17mm F1.8 doesn't. Just look at youtube video linked in this post.


20: http://youtu.be/V55M-c3CqCM

17: http://youtu.be/0gAN0Cenqrs

For reasons discussed in the rest of the thread you linked to, your evidence doesn't motivate your conclusion and does not refute the findings of the test I report here:


For those who haven't tried themselves, let me point out that it is very easy once you get precisely to the point where a lens starts hunting, to set up things such that you can "show" (if you try hard enough) that one lens hunts and the other doesn't. Very, very small variations in the conditions will suffice. And much of the thread discusses the obvious bias against the 20/1.7 that your testing procedures manifest. See for example here:


That comment is obsolete because the test I linked to was done 4 months aftert the comment;

No it isn't obsolete because it demonstrates that you are actively searching for preconditions that support your prejudices. You tried test after test after test and they were all shown to be biased.

and I addressed all these concerns in the latest test.

No you didn't and/or added others.

As to videos, here's one showing how quickly the 20/1.7 ordinarily focuses (in poor light).


The testing procedures exemplified by the video are described in the first of the posts I link to above.

We discussed that multiple times - refocusing on the same target isn't good enough test.

Yes, we discussed that multiple times and I proved you wrong. As shown in the video I link to above, I turned the camera on and off between AF cycles for the second part of the test. That means that the camera has no idea of what it was previously focusing on and that the lens is no longer prefocused on the prior target.

BTW, there is possible explanation of why 20mm hunts more often than other lenses:

It doesn't, so there is no need for an explanation of why it does.

AF motor noise means vibration. Since AF samples are taken during focus element motion, vibration makes the samples blurry. This makes it difficult to find contrast peak. The peak can be missed and then lens starts to hunt.

Apparently, you overlooked that the time it takes to scan a single line on the sensor for AF purposes is far too short for that to matter with any AF lens (none of which entirely vibration-free).

Anyway, I argued enough about this topic in the past.

So did I. So I suggest we just let people have a look at the evidence and decide for themselves.

Few months ago I switched from 20mm F1.7 to 17mm F1.8 mostly because of poor AF performance of the 20mm. Can't be happier now - no AF hunting anymore.

Glad that you are happy. Personally, I don't have any hunting with the 20 and enjoy the superior sharpness you have helped showing that it possesses.

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