Fujifilm X100S Optics

Fixed focal-length lens
Excellent far-field performance from the 35mm equivalent fixed lens.

The Fuji X100S has a fixed, 23mm f/2 wide-angle lens with an equivalent focal length of 35mm because of the X100S APS-C sensor's ~1.5x crop factor. Sharpness and contrast are very good across the frame at f/8, with very low levels of coma distortion, negligible chromatic aberration and flare, and very little softening in the corners. Excellent results here.

Macro
The Fuji X100S captured a larger-than-average minium area, with very good detail. The flash throttled down well, but was partially blocked at minimum distance.

The X100S captured a somewhat larger-than-average minimum area measuring measuring 3.07 x 2.05 inches (78 x 52 millimeters) at its closest focus distance. Details are very good over much of the frame at f/8, and corners show only a bit of softening. (Most lenses have some softening in the corners at macro distances, so the X100S's lens did much better than average here.) The Fuji X100S's flash throttled down fairly well producing a good exposure, but the flash is partially blocked at closest distance, causing a dark shadow in the bottom-left of the frame. The other corners show moderate shading.

Geometric Distortion
Low to moderate distortion from the Fuji X100S's fixed, wide angle lens.

The Fuji X100S's 35mm equivalent lens produced just over 0.2 percent distortion along the top and bottom edges which is lower than average, especially for a wide-angle lens. Vertical pincushion along the sides is moderate, though, at about 0.6% percent. Its complex nature (barrel in the center and pincushion near the edges for horizontal edges, stronger pincushion for vertical edges) makes it more difficult to correct in software without lens profiling, though it's low enough that it probably requires no correction for all but the most critical applications. The camera does not appear to be applying geometric distortion correction to its JPEGs, as RAW files contain identical amounts. 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). A very good performance here.

Chromatic Aberration and Corner Softness
Low chromatic aberration in JPEGs, though higher in uncorrected RAW files. Minor blurring in corners when wide-open.

Chromatic Aberration. Chromatic aberration in the corners of JPEGs is very low and dull, and hardly noticeable. In the center, it was practically nonexistent. (This distortion is visible as a slight colored fringe around the objects at the edges of the field of view on the resolution target.)

Corner Softness. The Fuji X100S's lens produced some blurring in the corners wide-open at f/2.0, though it was fairly minor but it did extend pretty far into the frame. Flare as well as the camera's C.A. removal caused high-contrast edges to be less defined in the corners, while corner shading reduced overall contrast, contributing to the appearance of softness. The center of the image however was quite sharp and contrasty. At f/5.6 and f/8, corners are only slightly softer than the center, which was very sharp. Very good performance here. As mentioned above, a small amount of corner shading ("Vignetting") is visible in JPEGs wide-open, as indicated by the dimmer corner crop. (More on corner shading below.)

Chromatic Aberration Correction. The Fuji X100S appears to suppress chromatic aberration during JPEG processing, as do quite a few cameras these days. Above are crops comparing an in-camera JPEG (left) to the matching RAW file converted with dcraw. (We suspect Adobe Camera Raw may be doing some CA correction under the hood that can't be disabled, as we see higher levels in RAW files converted with dcraw.) As you can see, C.A. is almost nonexistent in camera JPEGs, but moderate in the dcraw conversion. When we converted the same file using Adobe Camera Raw, a little more C.A. could be seen compared to the camera JPEG, but it was quite low, only about 1 or 2 pixels of fringing, almost as if it was slightly overcorrected.

Corner Shading Correction. We suspect the Fuji X100S also applies corner shading to JPEGs as well. Again, Adobe Camera Raw seems to apply similar correction to converted RAW files, however we see a greater difference in brightness in the center versus the corners in dcraw conversions.

Accuracy
Very good accuracy from the electronic viewfinder and LCD monitor, though the hybrid optical viewfinder isn't very accurate.

The Fuji X100S's electronic viewfinder and LCD proved pretty accurate, both showing about 99% coverage. The hybrid optical viewfinder's framing guides showed very poor coverage at only about 91%, as well as a substantial offset in both the horizontal and vertical directions. However, when the shutter button is half-pressed and the camera focuses, the framing lines shift in response to subject distance. Alignment improved dramatically with the shutter button half-pressed, however coverage didn't (in fact, it was a little worse at about 90%, but it's difficult to tell because of the strong barrel distortion introduced by the viewfinder's optics). Coverage is thus below average compared to SLR optical viewfinders which typically offer 95% or better, but decent for a rangefinder camera.