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

Started 7 months ago | Discussions thread
micksh6
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Re: slowness
In reply to Anders W, 7 months ago

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.

http://www.dpreview.com/forums/post/52045407

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:

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

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:

http://www.dpreview.com/forums/post/51263360

That comment is obsolete because the test I linked to was done 4 months aftert the comment; and I addressed all these concerns in the latest test.

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

http://www.youtube.com/watch?v=qcQJ4sD5A98&feature=youtu.be

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.

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

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

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