Sony RX100 III Optics

Zoom
A shorter than average zoom, with above average performance.

The Sony RX100 III is equipped with a 8.8-25.7mm lens, offering a fairly limited optical zoom ratio of about 2.9x, translating to a 35mm-equivalent focal range of about 24-70mm. The lens is however very fast (bright), with a maximum aperture ranging from f/1.8 at wide angle to f/2.8 at telephoto, which is excellent for low-light shooting and provides reduced depth-of-field for better subject isolation. As is often the case with fast compact lenses, though, maximum aperture does fall-off rather quickly as you zoom, already reaching f/2.8 somewhere between 28 and 35mm equivalent. The following table reflects the maximum and minimum apertures as reported by the camera at popular focal lengths:

Far-field performance in general is quite good at f/5.0 as shown above, with good sharpness and contrast across most of the frame, low chromatic aberration (the RX100 III suppresses it) and only minor softening and coma distortion in the corners at full wide angle. Performance at full telephoto is even better with excellent sharpness and contrast across almost the entire frame, though some vignetting can be see in the extreme corners. See below for lab results 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 illumination is not centered and the lens casts a large shadow at minimum distance.

The Sony RX100 III captured a larger than average sized minimum area measuring 3.54 x 2.36 inches (90 x 60 millimeters). Sharpness over much of the frame is very good, but corners show quite a bit of softness even at f/8 (most lenses show some softening in the corners at macro distances). The flash did a good job throttling down, but illumination is not centered and the lens casts a large shadow in the bottom half of the frame. You'll likely want to use external lighting for the closest RX100 III macro shots.

Geometric Distortion
Very low distortion in camera JPEGs, but very high in uncorrected RAW files at wide angle.

Thanks to in-camera distortion correction, there's almost no geometric distortion in the RX100 III's JPEG files, though what distortion there is asymmetrical. At full wide angle, we measured just 0.04% pincushion distortion along the top edge, but about 0.1% barrel distortion along the bottom edge. At full telephoto, barrel distortion along the top edge is about 0.1%, increasing to about 0.2% along the bottom edge. Still, very low geometric distortion overall. 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 RawDigger, which does not correct for distortion. As you can see at wide angle, barrel distortion is extremely high, between 4.0 and 4.1% depending on which edge is measured, while telephoto shows complex, "moustache-shaped" pincushion distortion at a low 0.2 to 0.3%.

We expect to see fairly significant distortion in uncorrected RAW files in fast, compact lenses, as allowing 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 pixels are "stretched" during correction and where lenses are usually already a bit soft. Note that most RAW converters are capable of applying distortion correction automatically, as specified by the manufacturer.

Chromatic Aberration and Corner Sharpness
Low to very low chromatic aberration in JPEGs. The lens produces some soft corners wide-open, though corner sharpness improves stopped-down.

Chromatic Aberration. Thanks to effective in-camera chromatic aberration suppression, there's very little to virtually no CA to be seen in the corners at either wide angle or telephoto in JPEGs. As expected, though, uncorrected RAW files (see below) show much more CA than seen above.

Corner Softness. Wide-open at full wide angle, the lens showed a little decentering, with the upper corners showing more softness than the lower ones. The center is quite sharp, but softening from the upper corners extends a fair bit into the frame. At full telephoto, corner sharpness is better all around, but the pattern changed, with upper and lower left corners quite sharp and the lower right somewhat soft. The center is again quite sharp, as is most of the frame.

Vignetting. There's some vignetting (corner shading) as well, shown by how much darker the corner crops above are than those from the center, particularly at the telephoto end.

F5.6: As is often the case, stopping down a few 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 at full telephoto, though it's no longer present at wide angle.

Chromatic Aberration Correction

As you can see in the crops from uncorrected RAW images on the right (taken from ARW files converted with RawDigger), the RX100 Mark III's lens produces moderately high and bright chromatic aberration at both maximum wide angle and full telephoto. But the RX100 III's processor does a great job suppressing CA in camera JPEGs (crops on the left). Note that most RAW converters should also automatically suppress CA when converting the RX100M3's ARW files.

Overall, very good performance from the RX100 Mark III's lens, especially considering how fast (bright) and wide it is, though telephoto reach and macro performance isn't as good as its predecessors'.

Coverage
Excellent accuracy from the LCD monitor and electronic viewfinder.

The Sony RX100 III's LCD monitor and EVF both provide close to 101% coverage at full wide angle and essentially 100% at telephoto. This is excellent performance, especially considering the amount of geometric distortion correction taking place at wide angle.