Fujifilm X-Trans CMOS sensor
The XE-1 makes use of the same X-Trans sensor as the X-Pro1, which means using a non-standard filter pattern in front of the sensor. The result, according to Fujifilm, is minimal susceptibility to color moiré, which in turn allows the company to dispense with the anti-aliasing filter that's used by almost all other cameras. In principle, this means the X-E1 should be able to resolve more detail than Bayer-array cameras with a similar pixel count.
The color filter array
Almost all digital cameras use what it called a Bayer color filter array, named after the Kodak engineer who developed the pattern. Over the years it's proved to be an excellent way of capturing both color and detail in a scene. Essentially, it consists of a simple repeating pattern of four pixels, two of which are sensitive to green light, one to red and one to blue, in a square RGGB layout.
However, one problem with the Bayer array is its susceptibility to false color artifacts when faced with an image that contains finely-repeating patterns (such as textiles), caused essentially by interference between these patterns and the regular grid of photosites. This results in unsightly bands of color, and in most digital cameras is suppressed by the addition of an optical low pass (or 'anti-aliasing') filter in front of the sensor that blurs away the finest image detail. This reduces any moiré patterns, but with an inevitable loss of resolution.
Film never showed an analogous effect due to its random grain structure, and Fujifilm's engineers reasoned that modifying the sensors' color filter array to make it look more irregular would have a similar effect. The result is the X-Trans CMOS's 6x6 color filter array, with red, green and blue photosites on each row and column (diagrams courtesy of Fujifilm):
|The common 2x2 'Bayer' pattern used in most digital cameras||The 6x6 color filter array pattern of Fujifilm's X-Trans CMOS sensor|
Use of an unconventional CFA is not without its complications, though; most obviously, it demands a completely different de-mosaicing algorithm for RAW conversion. Rather than simply re-calibrating the Bayer conversion processes they have refined over a decade or more, the developers had to start again from scratch. There's greater potential for conversion artifacts in areas of the image that might require special treatment. Despite Fujifilm's plans to work with third-party Raw processor makers, many popular converters still don't support the X-Pro1, which is a problem that extends to the X-E1.
In reviewing the X-Pro1 we found Adobe Camera Raw's conversion fell below the standards we'd usually expect of it, and the Fujifilm-provided conversion software seemed to have more trouble properly de-mosaicing the X-Trans filter array. This looked like it might limit the XE-1's options for Raw shooters. However, just before publication of this review, Adobe released a new version of ACR that addresses most of our concerns, with a better, more natural rendering of fine detail (see our Raw page for more, as well as our more detailed article, Adobe's Fujifilm X-Trans sensor processing tested).
All-electronic X mount
As the second camera to offer Fujifilm's X-mount, the X-E1 offers few surprises to anyone who's been following recent developments in mirrorless camera systems, being an all-electronic bayonet mount with ten contact pins for communication between the camera and lens. X-mount lenses have traditional-looking aperture and focus rings, but these have no direct mechanical coupling, and do nothing when the lens is dismounted from the camera.
The X-mount's claim to fame, though, is an extremely short flange distance (from mount surface to sensor) of 17.7mm - shorter even than Sony's E-mount for its NEX system. The lenses themselves feature unusually short backfocus distances from the rear element to the sensor, and use large rear elements to maximize the illumination of the corners of the frame. The diagram below supplied by Fujifilm) illustrates this principle, here showing a simulated view of the 18mm prime mounted on the X-Pro 1: