Samsung NX 20mm f/2.8 i-Function

Samsung NX 20mm f/2.8 i-Function

I love the 20mm focal length on APS-C. It is a bit wider than a traditional “wide” 35mm and a bit tighter than a traditional 28mm. Stick this lens in a pancake package with a fairly large f/2.8 aperture and you have a nice compact package. Lets see how it performs.

This lens follows the same build quality as the kit lenses. It uses decent plastics, but not great. The iFn ring feels about the same, but thankfully it adds a metal mount. The mount still is only supported by only 3 screws, which shouldn’t be a problem on a small lightweight lens like this one, but 4 or 5 was more standard on most lenses. I have seen them with up to 8. The build quality is typical of a modern lens.

The lens is 6 elements in 4 groups, one of those aspheric. It is very light at 89g (3oz). It has a close minimum focus distance of 0.17m (0.56ft). The diaphragm has 7 curved blades. The tiny lens barrel uses Leica standard 43mm filters, which are easy to come by. The lens barrel extends slightly as you focus, but it doesn’t rotate so polarizers are fine to use without adjustment.

A bit of background on i-Function for those that haven’t used it. With a supported lens and body, if you hit the iFn button on the lens, the camera brings up a menu, if you hit it again it cycles through different functions like ISO, WB, EV compensation, image settings, etc. When your on the selected function, like ISO, you turn the focus ring and the ISO setting changes. This is a slick feature and makes use of the mostly useless manual focus ring (on these modern lenses) as a secondary command dial on the camera.

Optical Characteristics

Samsung uses in camera correction by design with their lenses, like the u4/3 system cameras do. What this means is they intentionally don’t correct all the distortion, vignetting, and lateral CA of the lens and correct it in software. The RAW file is left alone by Lightroom at this time. They don’t have profiles for all the lenses yet, but they do have some lenses in there so I think it is likely the rest of the profiles will show up at some point. For this reason I shot this test twice. Once with JPEG out of camera at default settings, and the second time with RAW. I will present the corrected data first, followed by the uncorrected data.

Corrected MTF 50 (Sharpness)

Corrected MTF 20 (Resolution)

Corrected Lateral Chromatic Aberration

Corrected Distortion

With the in camera corrections, the images have negligible barrel distortion of -0.17% (numeric average between all apertures), following shows the coefficients and a sample test chart.

All data gathered using Imatest.

Uncorrected MTF 50 (Sharpness)


f/2.8, 4, 5.6, 8

Uncorrected MTF 20 (Resolution)


f/2.8, 4, 5.6, 8

Uncorrected Lateral Chromatic Aberration


f/2.8, 4, 5.6, 8

Uncorrected Distortion

Without the automatic corrections, the lens has extreme barrel distortion of -4.5% (numeric average between all apertures), following shows the coefficients and a sample test chart.

All data gathered using Imatest.

Conclusion

It is difficult to rate auto corrected lenses. With Olympus, Lightroom automatically corrects the distortion before you are even presented with the “RAW” data, but with the Samsung Lightroom leaves it alone. If you have Lightroom 3 you can use manual adjustments to correct out the distortion until Adobe provides the lens profile for the 20mm.

Looking at the corrected data, the lens is extremely sharp in the center throughout the range. The edges are poor wide open and slowly improve to decent, but most of the frame is pretty good. Both the MTF50 and 20 characteristics are similar. Lateral CA and distortion are both non issues with the corrected lens.

Looking at the uncorrected data, the lens has good to very good resolution across the frame at all apertures, but MTF 50 suffers at the corners. Lateral CA is noticeable, but not terrible, still better than many uncorrected lenses at this focal length. However, there is extreme barrel distortion of about -4.5%, not quite fish-eye but will be noticeable in many shots. It is about the same as the 17-18mm end on many kit lenses.

Longitudinal CA in the bokeh is noticeable at f/2.8, but pretty much gone by f/5.6. It is magenta in front and green behind the focus point. There is some color fringing wide open around bright lights, but it improves a lot stepping down.

The lens also shows some coma and astigmatism wide open, but it improves on stepping down.

The lens is basically immune to flare. I tried placing the sun just outside the upper left corner, at the rule of thirds point, and at the corner. All of these tend to flare. No flare was visible. The sun was slightly shrouded by clouds, so I will try again with no clouds, but overall the flare resistance seems very good.

Bokeh looks nice. As with any lens it can become hectic in certain situations, but doesn’t seem bad for a 20mm f/2.8 lens. Since bokeh is largely personal taste, please look at the sample images in the Zenfolio gallery.

Autofocus is faster than any of the kit lenses indoors due to the larger aperture. It can still have trouble locking indoors though. Autofocus in normal light is very quick, as are all cameras.

Measured Focal Length (changes with correction of barrel distortion):
Corrected: 21.4 mm at 1:53 magnification
Uncorrected: 20.0 mm at 1:57 magnification

Pros:
– Compact size standard
– Excellent Center Performance
– Flare Resistance

Cons:
– Corners below f/5.6

Uses (sample):
– General Wide Angle
– Subtle Carry

The distortion correction has a noticeable impact on corner performance due to the relatively extreme degree of correction (corners have to be stretched out). However, the nice compact size and good central performance make this lens a good buy, and the lens performs in-line with 20mm class lenses from other manufacturers.

Look for my Samsung NX Kit lens shootout (20-50, 18-55, and 18-55 II) and my 30mm f/2 review in the next few weeks.

If you like my review, you might shop for camera gear at Adorama.

The gallery images are © 2011 Eric Tastad, and may only be used for personal evaluation of the lenses.

Visit the Zenfolio gallery to download originals. These are straight from the camera: JPEG, Fine, 14MP, Standard (no adjustments).

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