Panasonic 20mm f/1.7 ASPH LUMIX G

Name: Panasonic 20mm f/1.7 ASPH LUMIX G
Brand: Panasonic
Rating: 9.1 (22 reviews)

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Lens Review
Specifications
Description

20mm	$367 average price

Lab Test Results

Olympus E-P1

Blur
Chromatic Aberration
Vignetting
Geometric Distortion

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SLRgear Review
September 30, 2009
by Andrew Alexander

The Panasonic 20mm ƒ/1.7 was introduced alongside the GF-1, to provide an extremely compact shooting solution. The lens is very small, owing to its efficient optical layout (seven elements in five groups) and micro-four thirds lens mount.

The lens is only compatible with micro-four thirds camera bodies, and mounted on such a camera it will produce an effective field of view of 40mm. The lens takes 46mm filters, and will be available in October 2009 for approximately $400.

Sharpness
We tested the Panasonic 20mm ƒ/1.7 on the Olympus E-P1, as we had that camera body standardized for lab testing. In our initial handling we had the impression the lens was quite sharp, and our full range of tests bear this out.

The lens is at its sharpest at ƒ/2, but the difference between ƒ/2 and ƒ/8 can only be measured in tenths-of-blur units. Between ƒ/2 and ƒ/8, we note sharpness between 1 and 1.5 blur units. With the lens set wide open to ƒ/1.7, there is some light corner softness, with a generous sweet spot of sharpness and corner softness only presenting itself in the extreme edges of the frame. In the corners, we note about 2 blur units of sharpness.

Diffraction limiting technically starts in at ƒ/8, but isn't statistically noteworthy until ƒ/11. In practical usage, you won't see a difference unless you use the lens fully stopped-down at ƒ/16, where we note about 2 blur units of sharpness across the frame.

Chromatic Aberration
The lens is quite resistant to chromatic aberration, showing only slight magenta fringing in areas of high contrast in the corners of the image.

Shading (''Vignetting'')
If there's a weakness in the lens, it would be significant corner shading when used at larger apertures. This is especially noticeable when used wide open, where we note corners which are a full stop darker than the center of the image. This light falloff reduces as the lens is stopped down, becoming 3/4 of a stop at ƒ/2, and 1/2 a stop at ƒ/2.8. At ƒ/4 it remains more or less constant at a third-of-a-stop of light falloff.

Distortion
We've confirmed that the Olympus E-P1 performs some image post-processing in camera, reducing the effect of distortion. Our testing shows that for the 20mm ƒ/1.7, distortion is almost non-existent, at just +0.1% barrel distortion in the corners.

Autofocus Operation
The Panasonic 20mm ƒ/1.7 takes about one second to focus from infinity to closest focus. It focuses with a slight whirring noise and vibration which can be felt while holding the camera; nothing disconcerting, just noticeable, owing to the small size of the camera. Short focus throws happen very quickly. Interesting, we felt that the lens focused faster on the Panasonic GF-1 than on the Olympus E-P1, though this was totally anecdotal.

Macro
Macro performance is nothing to write home about here: just 0.13x magnification, with a minimum close-focusing distance of 20cm (about 8 inches).

Build Quality and Handling
It's almost hard to get used to the diminutive size of micro-four thirds products, and this isn't made any easier by the especially small size of the Panasonic 20mm ƒ/1.7. (Years from now, we'll be starting sentences with, "Back in my day, lenses weighed over a pound and were this long...) The lens weighs only 100 grams, just three and a half ounces. As our technician Rob says, this lens could easily fit in a pocket... even a shirt pocket. Mounted on either the GF-1 or the E-P1, the combination is extremely handy and easily transportable. The lens mount is metal, the 46mm filter threads are plastic, and it doesn't seem to ship with a lens hood (we're not sure if one is even available).

The lens is devoid of any switches or control surfaces other than the manual focus ring; there isn't much room for anything and in the micro-four thirds cameras it can attach to, lens functions are controlled at the camera level.

The focusing ring is plastic with deep ribs, about a half-inch wide. The lens uses a fly-by-wire design for the focusing ring, so there is no direct mechanical connection between the ring and the focusing lens element. The result of this is that the focusing ring has no stops at either the infinity or close-focusing end. Consequently we can't report on things like focusing range, or whether the lens focuses past infinity. Manual focusing is quite responsive with a high degree of sensitivity: rotate the ring slowly, and you get a lot of fidelity while focusing, for very slight adjustments. Rotate it quickly, you go through the range very quickly. While focusing, there is a very slight amount of lens extension, but the front element does not rotate.

Alternatives

Olympus 17mm ƒ/2.8 M.Zuiko Digital ~$300
The only other prime designed specifically for micro-four thirds at the time of writing, the Olympus 17mm is a slower lens (ƒ/2.8 instead of ƒ/1.7) but offers a slightly wider field of view. The lens is slightly smaller than the Panasonic 20mm and the Panasonic easily bests it in terms of sharpness, resistance to chromatic aberration, and distortion. To its favor, the Olympus shows less corner shading than the Panasonic.

Panasonic 25mm ƒ/1.4 ASPH Leica D SUMMILUX ~$900
We haven't yet tested this lens, but with an adapter it should mount on a micro-four thirds camera body. The result would be effectively a 50mm ƒ/1.4, though with the adapter it could be a fairly bulky combination, especially compared to the 20mm ƒ/1.7.

Olympus 25mm ƒ/2.8 Zuiko Digital ~$240
With an adapter, the Olympus 25mm ƒ/2.8 should mount on micro-four thirds bodies. While a slower and longer lens (ƒ/2.8 vs ƒ/1.7, and 25mm vs 20mm) the lens is slightly less expensive. At ƒ/2.8, the Panasonic is easily sharper, but stopped down to ƒ/4 and beyond the two lenses are comparably sharp. The Panasonic is also more resistant to chromatic aberration and produces less distortion, though the Olympus shows less corner shading.

Sigma 30mm ƒ/1.4 EX DC HSM ~$400
It would take an adapter, but in theory you should be able to mount the 4/3ds version of the 30mm ƒ/1.4 on a micro-four thirds body. The result would be an effective 60mm ƒ/1.4, though the combination might look a little ungainly (the 30mm ƒ/1.4 is a large lens when compared to the small size of the m4/3 bodies). That said, the 20mm offers a wider field of view, and looks to be sharper than the 30mm.

Conclusion
With excellent results for sharpness, resistance to chromatic aberration and essentially no distortion, Panasonic has done well with the 20mm ƒ/1.7, and we've been having fun shooting with it. For a really compact shooting package, the lens is a worthwhile investment.

Sample Photos

The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.

Still Life shot

VFA target

As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.