Camera/lens focus speed test (also about 20mm F1.7)

Started Mar 17, 2013 | Discussions thread
micksh6
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In reply to micksh6, Aug 25, 2013

So, I have redone the test with more consistent conditions and different settings. Instead of rotating the camera I switch targets and I measure AF start by AF assist light and focus end by green circle on LCD.
Camera and main target are fixed, this ensures consistent position of targets relative to camera. Tested Pana 20mm F1.7, Oly 45mm F1.8, 17mm F1.8, and 14-42mm II zoom.

The light was ISO 1600, 1/20s and F2.0 for the main target (yellow pig or chicken), slightly lower for secondary target (printed high contrast repeatable logo).
The reason for such low light is that with brighter light (1/30s, same ISO and F number) E-PL5 doesn't consistently turn on AF assist light and I needed AF light to measure AF speed. The AF light is covered by blue electric tape.

Of course the new test shows that all previous accusations in biasing against Pana 20mm were pure BS. I got many videos with focus target positioned differently relative to AF rectangle and AF rectangle moved from the center of the frame. I only upload 3 videos tonight because it takes too much time. More later.

In previous test I actually was favorable to Pana 20mm lens because, as I showed in this thread, Pana 20mm is not the sharpest in center. In videos I uploaded tonight the AF box is at dead center, but if you move it slightly off center the lens will focus a bit faster and hunt a bit less (not enough to get close to AF speed of other primes, of course).
So, my previous tests were perfectly valid, except that Pana 20mm should behave a bit worse if AF box is placed at center.

Pana 20mm lens starts hunting with no reasons when other lenses don't hunt. You can see that conditions are the same, camera is on tripod and target is static. Sometimes it hunts for focus, sometimes it doesn't. Other lenses focus consistently. I can't really explain why this happens, this is only a confirmation of a fact that many observed but some don't believe in.

I don't even need to count frames; you can very well see everything on video, the whole hunt fest (that's why the video is so long, sorry):
Panasonic 20mm: http://youtu.be/V55M-c3CqCM

And this is how a good lens should focus in low light. Oly 17mm F1.8, see the difference: http://youtu.be/0gAN0Cenqrs

Here is Oly 45mm F1.8. Very fast focusing forwards, but takes extra steps focusing backwards. Still, no hunting and closer AF target got a bit less light: http://youtu.be/t1jIyFD6YPI

This shows difference in focus algorithms and why it doesn't make sense to test lens focus speed when refocusing from the same position, or from infinity. Camera (E-PL5 in my case) takes different paths for refocusing from different distances. This test is close to real life scenarios.

While some may consider ISO 1600, 1/20s, F2.0 light too dim for anything, the difference is AF speed will be there even in brighter light. Even Olympus kit zoom 14-42mm II focuses faster than Pana 20mm under such light. But, with slightly lower light - ISO 1600, 1/15s, F2.0 the kit zoom can't focus at all because its maximum aperture is too slow - F3.9 at 18mm.

PS. Thanks to Mjankor for suggesting the test plan here http://www.dpreview.com/forums/post/51263403

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