Canon S100 Optics

Zoom
A wider-than-average 5x optical zoom lens, with good performance.

The Canon PowerShot S100's lens is both wider and longer than the S95's, covering the equivalent of about 24-120mm zoom on a 35mm camera compared to 28-105mm for its predecessor. The new lens is just as fast at wide-angle (f/2.0), but understandably slower at full telephoto (f/5.9 vs f/4.9). Details are good but a little soft in the center of the frame at full wide-angle (24mm eq.) and f/5.6, with some blurring and coma distortion in the extreme corners, though very little chromatic aberration is visible. Some flare is also evident around the bright white elements of this shot. At medium focal length (~56mm eq.), overall sharpness is slightly better, though extreme corners are still soft. Flare isn't as noticeable, though the exposure wasn't as bright as the wide-angle shot, so there aren't as many strong highlights. Results at full telephoto are a bit better with just a little corner softening, though the image is still a touch soft overall. Flare isn't as evident, and again, chromatic aberration is negligible. The Canon S100's digital zoom (up to 4x) does a pretty good job of maintaining fine detail at about 2x shown above, though we wouldn't recommend using higher magnifications due to further image degradation.

Macro
A slightly smaller than average macro area, with very good detail and resolution. Flash had some difficulty throttling down, and is partially blocked by lens.

The Canon PowerShot S100's macro setting captured a slightly smaller than average area of 1.80 x 1.35 inches (46 x 34 millimeters). Detail and resolution were both pretty good, though there's some softening in the extreme corners from field curvature of the lens. (Most cameras have some softening in the corners in macro mode. What we see here is better than average.) The Canon S100's flash had some difficulty throttling down at this distance, causing overexposure where the flash wasn't blocked by the lens. The overexposure plus the shadow from the lens resulted in a very unevenly lit image. Plan on using external lighting for the closest macro shots with the S100.

Distortion
Lower than average barrel distortion at wide-angle in JPEGs; very high at wide-angle in RAW files. Low distortion at telephoto.

JPEG: The Canon S100's 0.6% barrel distortion at wide-angle is actually fairly low compared to the average digital camera, especially considering its wide 24mm equivalent focal length (see below for the explanation). The distortion is however still noticeable in some shots. At the telephoto end, the S100's less than 0.1% barrel distortion is a little unusual as we'd normally expect to see pincushion distortion at telephoto. The amount is quite low at around 0.05%, and is barely noticeable. 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).

RAW: When converting RAW files using dcraw (which doesn't apply any distortion correction), barrel distortion at wide-angle is much higher, at about 4.2%. Distortion at full telephoto is about the same as the in-camera JPEG, so no correction was performed by the camera at the telephoto end. Canon's bundled Digital Photo Professional software automatically reduces geometric distortion (as does Adobe Camera Raw), producing distortion results very similar to in-camera JPEGs.

We expect high distortion at wide-angle for smaller lenses though, so it's nothing to be overly concerned about unless you are using a RAW converter which does not understand the embedded "opcodes" to perform distortion corrections automatically. There is however going to be some loss of resolution and possible interpolation artifacts as a result of such strong correction, because pixels in the corners of the frame are being "stretched" to correct for the distortion. Obviously, a lens that doesn't require such correction and is also sharp in the corners to begin with would be preferable, but relaxing constraints on distortion brings other benefits in the lens design, such as a compact, lower cost design.

Chromatic Aberration and Corner Softness
CA is low at wide-angle, and even lower at telephoto. Moderate blurring in the corners of the frame at wide-angle, but very good corner sharpness at full telephoto.

Chromatic Aberration. Chromatic aberration is quite low at both wide-angle and full telephoto, because the S100's DIGIC 5 processor removes most of it. See below of examples of uncorrected C.A. Chromatic aberration is a type of distortion visible as a slight colored fringe around the objects at the edges of the field of view on the resolution target.

Corner Softness. The Canon S100's lens produced moderately soft corners at full wide-angle. Blurring was about the same in all for corners, but softness didn't extend very far into the frame, and the center was quite sharp. We suspect much of the blurring is due to the CA and geometric distortion correction taking place at wide-angle. All four corners at full telephoto were sharp, as was the center. Some very minor vignetting is also noticeable at wide-angle and telephoto at maximum aperture, as can be seen from the darker corner crops.

Overall, this is good performance from a 24-120mm eq. digicam lens, but unfortunately as you can see from this shot, stopping the lens down to f/5.6 did not improve corner sharpness at wide-angle. (Again, likely because of the pixel "stretching" going on during geometric distortion correction, and the loss of edge contrast caused by CA suppression.)

CA Correction. Below are crops comparing in-camera JPEGs versus RAW files converted with Adobe Camera RAW 6.6 which doesn't appear to correct for CA in the S100's files (ACR does however correct geometric distortion to roughly match camera JPEGs):

As you can see, CA is very high and bright at wide-angle and moderate at telephoto (crops on the right), so the S100's DIGIC 5 processor is doing a great job at suppressing most of the CA in JPEGs. We're actually a little surprised Adobe Camera RAW 6.6 (final version) doesn't suppress CA like Canon's own software.

Coverage
Very good accuracy from the LCD monitor.

The Canon PowerShot S100's LCD monitor showed just over 100% coverage at wide-angle, and telephoto. Very good results here.