Sony RX100 Optics

Zoom
Good performance with the 28-100mm equivalent lens.

The Sony RX100 is equipped with a 10.4-37.1mm lens, offering a somewhat limited optical zoom ratio of about 3.6x for a premium subcompact, with a 35mm equivalent focal range of about 28-100mm. The beauty of this lens is its speed at wide-angle, offering a fast f/1.8 maximum aperture which is excellent in low-light and provides reduced depth-of-field for better subject isolation. Aperture drops off fairly quickly when you zoom, though. At the telephoto end, maximum aperture is f/4.9 which is on the slow side. The following table reflects the maximum and minimum apertures as reported by the camera:

Far-field lens performance in general is pretty good at f/5.6, with decent sharpness and contrast across most of the frame, low chromatic aberration (the RX100 suppresses it), though some minor flare and vignetting is visible. See below for comments on macro performance, geometric distortion, corner softness, etc.

Macro
A larger than average sized minimum coverage area, with very good detail. Flash throttled down well, but coverage is not centered and the lens casts a strong shadow at minium distance.

The Sony RX100 captured a slightly larger than average sized minimum area measuring 3.02 x 2.02 inches (76 x 51 millimeters). Detail was quite good in the center, and corners only showed a bit of softness (most lenses show some softening in the corners at macro distances, so the RX100 does better than most). The flash did a good job throttling down, but coverage is not centered and the lens casts a strong shadow in the lower right. You'll likely want to use external lighting for the closest RX100 macro shots.

Geometric Distortion
Very low distortion in camera JPEGs, much higher in uncorrected RAW files.

Thanks to in-camera distortion correction, there's almost no geometric distortion in the RX100's JPEG files. At wide-angle, we measured just 0.08% pincushion distortion, and at telephoto, it was essentially unmeasurable (0.02% or less). This is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide-angle) or inward (like a pincushion -- usually at telephoto).

To see how much correction is taking place in the camera, we converted RAW files from the above shots with dcraw, which does not correct for distortion. As you can see, at wide-angle, the barrel distortion is extremely high at about 3.8%, while barrel distortion at telephoto is a relatively low 0.5%.

It's not at all unusual these days to see fairly significant distortion in uncorrected RAW files, as this gives the lens designers greater flexibility in optimizing center sharpness and other aberrations, as well as in reducing cost, size, and weight. The downside is that the distortion correction contributes additional blurring to the corners of the frame, where lenses are usually already a bit soft. Also, if you're using a RAW converter that doesn't understand the embedded "opcodes" to perform distortion corrections automatically, you'll have to make the corrections manually in your image-editing software. Most RAW converters these days are capable of applying distortion correction automatically, as specified by the manufacturer.

Chromatic Aberration and Corner Sharpness
Moderately low chromatic aberration at wide-angle; even lower levels at full telephoto. The lens produced some soft corners wide-open, though corner sharpness improved stopped-down.

Chromatic Aberration. Thanks to in-camera aberration correction, there's very little to virtually no chromatic aberration to be seen in the corners with the RX100's lens at either wide-angle or telephoto settings. Note that the RX100 suppresses CA, as uncorrected RAW files show a good bit more CA than seen above.

Corner Softness. Wide-open at full wide-angle, the lens showed a little decentering, with the lower right corner quite sharp, and the upper left one rather blurry. At telephoto, corner sharpness was better all around, but the pattern changed, with the lower left corner being the sharpest, and the upper right the softest.

There's some vignetting (shading) as well, shown by how much darker the corner crops above are than those from the center. You can also notice a color shift from wide-angle to full telephoto, especially in the corners, but that's a fairly common occurrence, made worse when you set manual white balance at one end and shoot at the other.

As is usually the case, stopping down a couple clicks significantly improved corner performance at both wide-angle and telephoto, however the same corners were still softer than the others due to decentering. We can also still see some vignetting as well as the color shift mentioned previously.

Coverage
Excellent accuracy from the LCD monitor.

The Sony RX100's LCD monitor showed essentially 100% coverage at full wide-angle and telephoto. This is excellent performance, especially considering the amount of geometric distortion correction taking place at wide-angle.