Sony rejuvenated the premium compact market in 2012 when it introduced the Cyber-shot DSC-RX100. The RX100 took a 1"-type sensor and relatively fast zoom lens and put it into a body that can slip into your pocket. Every year since has seen the arrival of a new RX100 model. The RX100 II added a new BSI CMOS sensor and hot shoe. Last year's RX100 III lost the hot shoe but gained a faster (but shorter) lens and clever pop-up EVF. The latest model inherits all of those things but adds a new stacked CMOS sensor that, according to Sony, is literally years ahead of the competition.

While we'll get into the technology behind the new Exmor RS stacked CMOS sensor below, here are the major benefits. All the camera's main capability increased come from the enhanced speed of the new sensor. This translates into incredibly fast continuous shooting (16 fps to be exact) and high frame rate video (up to 960 fps), as well as support for 4K video recording with full pixel readout. And, when the Exmor RS is used in electronic shutter mode, the faster readout means there's less of a delay between starting to read the sensor and finishing: meaning rolling shutter is essentially eliminated.

We'll look at the ways that Sony is trying to turn fast readout into photographic benefits throughout this review. For now let's take a look at the RX100 IV's standout features:

Sony Cyber-shot DSC-RX100 IV key specifications

  • 20.1MP 1"-type stacked CMOS sensor
  • F1.8-2.8 24-70mm equivalent Zeiss Vario-Sonnar T* lens
  • Optical image stabilization
  • 1/32000 sec max shutter speed (1/2000 using mechanical shutter)
  • 16 fps continuous shooting (with metering and focus fixed at the first shot)
  • Slow motion video recording up to 1000 fps (960fps in NTSC mode)
  • 4K (UHD) video recording with full sensor readout and bit rates up to 100Mbps
  • Picture Profile modes including S-Log2 gamma setting
  • Dual recording captures 17MP stills while recording up to 1080/30p video
  • Tilting 3" LCD with 1.3m dots
  • Pop-up 2.36m dot OLED electronic viewfinder
  • Built-in ND filter (with Auto mode)
  • Wi-Fi with NFC

All of the tried-and-true features from the RX100 III have made their way to the Mark IV, including its 24-70mm equivalent F1.8-2.8 lens, tilting 3" LCD, ND filter, and Wi-Fi. The body is identical except for the lettering on the top.

Everything else is an upgrade, mostly due to the new sensor. The non-sensor-related features include an electronic shutter, Picture Profiles including S-Log2 support, higher video bit rates, and a sharper EVF. The RX100 IV also has more advanced Auto ISO control.

Card requirements:

Because so many of the RX100 IV's features produce large amounts of data, you can only use all its features if you use specific SD cards. The main limitation isn't just one of speed, it's the size of file that the card can cope with. Only one of the five cards in the picture below allows the full use of the camera's capabilities (and it's not the fastest).

The RX100 IV's high frame rate and high bitrate movie modes create large files, so you need to use an SDXC card to use them. It doesn't matter how fast your card is or if it uses a UHS interface: if it says SDHC on the front, it won't allow you to use these modes.

Then comes the question of speed. A conventional SDXC card rated as Class 10 or an SDXC UHS-I card rated at U1 (which is an equivalent speed rating), will allow you to shoot HFR video and X AVCS video at up to 60Mbps. To shoot 4K or 1080/120p at 100Mbps, you'll need a UHS-I (or II) card rated as speed class U3.

Card Type High Frame Rate Video X AVCS video up to 60Mbps X AVCS video
100Mbps
SDXC Class 10
Y
Y
N
SDXC UHS-I or II Class U1
Y
Y
N
SDXC UHS-I or II Class U3
Y
Y
Y
SDHC Class 10
N
N
N
SDHC UHS-I or II Class U1
N
N
N
SDHC UHS-I or II Class U3
N
N
N

In short: you'll need to buy an SDXC UHS I or II card rated as speed class U3 in order to make full use of the camera. A (sarcastic) round of applause to the SD Card Association for making all of that so clear.

RX100 IV vs RX100 III key differences

 
Sony RX100 IV
Sony RX100 III
MSRP $949 $799
Sensor 20.1MP 1"-type stacked CMOS 20.1MP 1"-type BSI CMOS
ISO range
125-12800 (expands to 80-12800)
EVF resolution 2.36M dot 1.44M dot
Maximum shooting rate 16 fps 10 fps
Maximum shutter speed 1/32000 sec * 1/2000 sec
Anti Distortion Shutter Yes No
Auto ISO rate-of-change control Yes No
Top video resolutions (NTSC) 3840 x 2160 (30p)
1920 x 1080 (120p/60p/30p/24p)
1920 x 1080 (60p/30p/24p)
1280 x 720 (120p)
Max video bit rate (codec) 100Mbps (XAVC S) 50Mbps (XAVC S)
High speed video Up to 960 fps ** N/A
Dual recording Yes No
Picture Profiles (for video) Yes No
S-Log2 gamma Yes No
Battery life (CIPA) 280 shots 320 shots
* Camera uses electronic shutter above 1/2000 sec
** Video is upscaled to 1080p. Recorded resolution depends on frame rate.

As you can see, the RX100 IV blows away its predecessor in all but two areas. One is battery life, which is about 14% lower than the RX100 III. Something that's gone up is the price, which is nearly $1000.

Exmor RS stacked CMOS sensor

In case you haven't noticed, the biggest story on the RX100 IV is its new Exmor RS stacked CMOS sensor. But first, a history lesson.

Original (front-side illuminated) CMOS sensors, such as the one found in the original RX100, had both its photo-diodes and image processing circuitry in one layer. The RX100 II switched to a BSI, or back-illuminated sensor, which Sony branded as Exmor R. This technology flipped the chip over to push most of that circuitry to the back (hence the name). This allowed for a larger surface on which to capture light, which in turn improves the signal-to-noise ratio, allowing for a noticeable improvement in both still and video quality.

The 'stacked' design frees up space to move the high-speed processing circuitry [2] from the edge of the chip, to behind the pixels themselves [1]. This more extensive circuitry and its proximity to the pixels is what gives the Exmor RS its additional speed.

Then, to prevent the Bionz X image processor being overwhelmed, Sony has built some DRAM memory [3] into the back of the sensor, to act as a buffer.

The Exmor RS sensor on the RX100 IV takes things one step further, building up the sensor by essentially gluing layers together. This creates more space behind each pixel so that the high speed processing circuitry can be fitted into the middle of the chip, rather than the data having to work its way to the edges, first. This allows much faster data readout (Sony says more than five times the speed of the existing Exmor R sensor).

However, since the Bionz X processor can't cope with all this additional data, Sony has also built some DRAM memory into the back of the chip, acting as a buffer to store the data and feed it to the image processor at a speed it can handle. This increased speed helps explain many of the features Sony has wrung out of the camera: reduced rolling shutter, 4K video, high frame rate video, faster continuous shooting and Dual Record.