Sensor and Lens

Fujifilm X-Trans CMOS II sensor

The X20 uses an all-new sensor which, like the X10's, is of the 2/3" type, and is therefore larger than those used in most of its competitors (see diagram below). But instead of its predecessor's EXR design, it gets Fujifilm's latest 'X-Trans' color filter array, as used in the company's X-Pro1 and X-E1 mirrorless models and the X100S fixed-lens APS-C compact. This doesn't use an optical low-pass filter, and according to Fujifilm should give higher resolution than conventional Bayer-type 12MP sensors. You can read more about X-Trans technology in our Fujifilm X-E1 review.

The common 2x2 'Bayer' pattern used in most digital cameras The 6x6 color filter array pattern of Fujifilm's X-Trans CMOS sensor

The sensor is also of the 'backside-illuminated' type, which places the photodetectors on the opposite side of the chip from their associated circuitry. This promises better light-gathering capability, which should mean improved noise performance compared to conventional (and at this point mostly last-generation) small-format CMOS sensors.

On-chip phase-detection autofocus

This cross section of the X-Trans CMOS sensor shows the following:

1) Microlenses
2) X-Trans color filter
3) Left/Right light interception filter
4) Phase detection sensor / green filter pixel
5) Photodiode

Diagram courtesy of Fujifilm

The second addition to the sensor design is an on-chip phase detection system for faster autofocus. The phase detection system works hand-in-hand with more conventional contrast detection, making this a 'Hybrid AF' system. Fuji hasn't disclosed when the camera switches between Hybrid and regular contrast detect AF, but we believe that it's likely when light levels drop below a certain level.

Fujifilm is promising AF speeds as fast as 0.06 seconds which, if true, is a significant improvement over the X10. The F300EXR which previously used this technology was very quick indeed, and the BSI design means the phase detection pixels gather as much light as possible. We'll see how the X20 performs later in this review.

Sensor sizes compared

The diagram below compares the size of the X20's 2/3" sensor to those in its nearest competitors - and larger sensors offer potential for better image quality. The X20's sensor is half the size of that found in the (much more expensive) Sony RX100, but still 50% larger than the Canon G15's.

The X20's 2/3" sensor is half the area of the Sony RX100's 1" sensor, but about 50% larger than the 1/1.7" sensor used on most of its competitors.

Lens overview

The Fuji X20 features the same 28 - 112mm equivalent, F2.0-2.8 lens as its predecessor. The lens construction compirises 9 elements in 11 groups, and features a 'High Transmittance Electron Beam Coating' to reduce flare and ghosting.

Like most of its peers, the X20 features an in-lens shutter. Such shutters are rarely able to offer their
fastest shutter speeds at large apertures, but the X20 has a way around this limitation. In shutter priority, aperture priority or manual mode, it will use its electronic shutter mode to offer its fastest shutter speed at all apertures. For example, at F2.0, the X20 will switch to the electronic shutter above 1/1000 sec, with the shutter speed indicated in red on the LCD. This is not the case in Program mode, however, where it will stop the aperture down and continue to use the physical shutter.

As mentioned earlier, the lens is controlled with a manual zoom ring, which is a rarity on a compact camera. Unfortunately, there's no manual focus ring around the lens.

If you attach the optional lens hood (model LH-X10), you'll be able to screw on the 52mm filter of your choice.

28mm, F5.6, 1/850 sec, +0.3 EV, ISO 100 112mm, F7.1, 1/900 sec, +0.3 EV, ISO 100

The X20's lens offers a minimum focus distance of 10 cm at wide-angle and 80 cm at telephoto when in its standard macro mode. If you jump into super macro mode (which instructs you to adjust the lens to full wide-angle), that distance drops to just 1 cm.

As you'd expect, this lens has an optical image stabilizer built right into it. Fujifilm says that the OIS system can reduce the effects of camera shake by four stops.

Enthusiast compacts: lenses, sensors and background blur

The chart below may look confusing, but what it's trying to convey is how sensor size and lens speed combine in the different cameras in this class.. The X20's F2.0-2.8 lens is 'fast', allowing the use of fast shutter speeds and low ISOs even though, when you factor in the 2/3" sensor, it would be equivalent to an aperture range of around F8-F11 on a 35mm camera.

The combination of a fast lens and larger-than-average sensor gives the Fujifilm X20 some of the best depth-of-field control (not to mention light-gathering ability) in this group.

The X20 is one of the most capable compacts on the market, alongside the Olympus XZ-2 and Canon PowerShot G15. It offers greater potential to blur backgrounds at the long end of the zoom than the Sony RX100, despite that camera's larger sensor. This is because the RX100's lens gets quite 'slow' at its telephoto end.

x20
F2.8 @ 112mm (equiv) 100% crop of background

The equivalent apertures also give a rough idea of how the cameras might compare in low light; to a degree they indicate how a larger sensor on 'Camera A' should be offset by a faster lens on 'Camera B'. Obviously this isn't the whole story; the characteristics of the individual sensors matters too, as does the quality of in-camera processing for JPEG shooters. But the story is essentially the same - the X20's fast lens should in principle make it one of the most capable compacts on the market for low-light work.