Sony RX100 IV Optics

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

The Sony RX100 IV 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 some popular focal lengths:

Far-field performance in general is quite good at f/5.6 as shown above, with very good sharpness and contrast across most of the frame, low chromatic aberration (the RX100 IV suppresses it) and only minor softening and coma distortion in the corners at full wide angle. Performance at full telephoto is also quite good with good 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 the lens casts a large shadow at minimum distance.

The Sony RX100 IV captured a larger than average sized minimum area measuring 3.83 x 2.55 inches (97 x 65 millimeters) at maximum wide angle. 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 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 IV 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 IV's JPEG files. At full wide angle, we measured just 0.04% pincushion distortion. At full telephoto, barrel distortion is about 0.1%. 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, barrel distortion is extremely high, at about 3.9%, while telephoto shows low but complex "moustache-shaped" pincushion distortion at about 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 in lens profiles embedded in RAW files.

Chromatic Aberration and Corner Sharpness
Very low to moderately 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 moderately low to low C.A. 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 C.A. than seen above.

Corner Softness. Wide-open at full wide angle, the lens in our sample showed a little decentering, with the right-hand corners showing more softness than the left-hand ones. The center is very sharp, and softness from the worst-case corner (lower right) doesn't extend very far into the frame. At full telephoto, it's the lower corners that are soft, even showing some image doubling, and the softness extends far into the frame from the bottom (the top corners are much better). The center is fairly sharp at full telephoto, though not as sharp as wide angle.

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 sharpness, contrast and chromatic aberration at both wide angle and telephoto, however the same corners were still softer than the others due to decentering. Sharpness in the center at wide angle remained about the same, however C.A. was reduced to almost nonexistent. Sharpness and C.A. in the center improved at full telephoto, though wide angle is still a bit sharper. We can also still see some minor 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 dcraw), the RX100 Mark IV's lens produces moderately high and bright chromatic aberration at both maximum wide angle and full telephoto. But the RX100 IV's processor does a great job suppressing lateral chromatic aberration in camera JPEGs (crops on the left). Note that most RAW converters should also automatically suppress C.A. when converting the RX100 Mark IV's ARW files.

Overall, very good performance from the RX100 Mark IV's lens, especially considering how fast (bright) and wide it is.

Coverage
Excellent accuracy from the LCD monitor and electronic viewfinder.

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