Monday, 17 August 2015

New Lumix 20mm lens: Better focus ring

The Lumix G 20mm f/1.7 pancake is a classic Micro Four Thirds lens. Being the first Panasonic prime lens, it is widely considered to be very well performing. But it has some shortcomings: Due to the old fashioned focus design, where the whole lens assembly moves back and forth during focusing, the autofocus is rather slow. Also, the large focus assembly makes it very noisy when focusing.

In 2013, Panasonic updated the lens. It is well known that the new lens is largely a cosmetic redesign: The optical layout is the same, and the focus method is the same. But is the new lens better? The new lens is available in black and silver, and you can see the silver version to the right below:


Old (left) and new (right) versions of the Lumix G 20mm f/1.7

Design wise, I much prefer the old version, to the left. I don't like glossy lenses. The specifications are very similar, but the new one is lighter, even if it has a thin metal outer body:

LensLumix G 20mm f/1.7Lumix G 20mm f/1.7 II
Lens elements/groups7/57/5
Aperture diaphragm blades77
Minimum focus0.20m0.20m
Diameter63mm63mm
Length26mm26mm
Filter thread46mm46mm
Weight100g87g
Hood includedNoNo
Optical image stabilisationNoNo



The noise and autofocus speed is the achilles heel of the Lumix G 20mm f/1.7. To see if the new lens focuses faster, I have mounted both to the same camera, the Lumix GX7:


Used in this manner, I recorded this video to test the autofocus speed:



Even if the lenses behave slightly differently in this test, I think that neither is consistently better or worse. My conclusion is that they perform equally good, further suggesting that they do indeed have the same focus technology.

I have also tested them in terms of noise. I used an Iphone to test the noise, and tested the focus speed on a Lumix GM1. This was done by checking the focus delay when changing the focus from infinity down to 0.20m, the closest focus distance. Here is a video summary of the test:



And a summary of the findings:

LensLumix G 20mm f/1.7Lumix G 20mm f/1.7 II
Focus delay0.80s0.84s
Focus noise57dB50dB
Aperture change noise70dB72dB

Conclusion


The focus speed is very similar between the lenses. The difference I found is most likely not significant, it could be just due to random differences in the testing parameters. So my conclusion is: The lenses have exactly the same focus motor/assembly.

The focus noise, though, shows a significant difference. Both lenses are still noisy, by modern standards, but the new one less so than the old lens. Perhaps this is due to the use of different materials in some components. Whatever the cause, this is good news: Focus noise is less likely to be a problem with the new lens.

The aperture change noise shows some difference in my measuring, but I would say it's hardly significant. This noise is on a quite normal level for Micro Four Thirds prime lenses. Zoom lenses tend to be less noisy, as they have smaller apertures. I've found the most noisy aperture on the Leica 25mm f/1.4, not surprising since it has a very large aperture.

One difference which could be quite important, though, is that the focus ring is much better on the new lens. Outwards, they look the same, but the old lens has a focus ring which is prone to becoming sticky after a while, making it hard to focus smoothly.

The new lens, on the other hand, has a focus ring which feels much higher quality, more like that on the Leica 25mm f/1.4 (my test here).

The Lumix G 20mm f/1.7 is the lens I would not trust to focus well during video recording, especially in dim light. Hence, the manual focus capability is quite important, and you may benefit from the much smoother focus ring of the new lens.

Focus assembly


A closeup of the two lenses shows that they have the same outwards appearance in the focus assembly:


In both lenses, you'll see a small gap between the outer chassis, and the lens assembly. The inner tube moves in and out when changing the focus. Hence, you cannot mount a step up ring on the lens: It can cause the focus assembly to lock up. It has happened with me, so take care.

You can, however, mount a 46mm to 37mm step down ring as hood. This gives some basic protection of the front lens element, while keeping the overall package compact. If you go down this route, you also need a 37mm front lens cap.:


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