Canon G5X Optics

Zoom
A generous zoom ratio for its size and speed, with mixed optical performance.

The Canon PowerShot G5X's 4.2x zoom lens is the same as the G7X's, covering the equivalent of about 24-100mm on a 35mm camera. Maximum aperture is a very fast f/1.8 at wide angle to a fast f/2.8 at full telephoto.

The following table reflects the maximum and minimum apertures as reported by the camera:

Sharpness is very good in the center of the frame at full wide angle and f/5.6, but corners are a little soft, likely because of the strong distortion correction applied (see below). Minor chromatic aberration is visible as it is suppressed in JPEGs, though some flare is evident around the bright white elements of this shot. At medium focal length (~50mm eq.), far-field performance appears to be very good at f/5.6 with excellent sharpness and contrast, and flare doesn't appear to be an issue. Results at full telephoto and f/5.6 are quite good, with very good sharpness and contrast across the frame. Again, chromatic aberration is negligible because the G5X suppresses it in JPEGs, though we have seen some significant purple or red fringing around strongly backlit subjects in some shots.

The G5X also offers digital zoom up to 4x, and what Canon calls a "digital teleconverter" at preset magnifications of 1.6x and 2.0x, though as is always the case, there is a noticeable loss in image quality with digital zoom, especially at the maximum setting.

Overall, decent far-field performance at f/5.6. See below for our lab results.

Macro
A larger than average macro area, with very good detail in the center. Flash overexposed and is partially blocked by the lens at closest focus.

The Canon PowerShot G5X's lens captured a larger-than-average minimum area of 2.99 x 1.99 inches (76 x 51 millimeters), a little smaller than the area we captured with the G7X. Sharpness is very good in the central area of the frame, though corners and edges are very soft from field curvature. (Most cameras have some softening in the corners in macro mode, but usually not this much.) The Canon G5X's built-in flash is partially blocked by the lens at closest focus distance, resulting in a very dark shadow at the bottom and overexposure at the top. You'll likely want to stick to external lighting for close macro shots with the G5X.

Distortion
Lower than average distortion in JPEGs; very high at wide angle in uncorrected RAW files.

JPEG: The Canon G5X's just under 0.4% barrel wide angle is low compared to the average digital camera, especially considering its generously wide 24mm-equivalent focal length (see below for the explanation). The less than 0.1% barrel distortion at the telephoto end is very low and not the pincushion type of distortion we normally see at telephoto. 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).

Uncorrected RAW: When converting RAW files using RawDigger (no corrections applied), we see that actual barrel distortion at wide angle is extremely high, at about 4.9%. Also note how the image circle does not cover the corners of the sensor at maximum wide angle, leaving them very dark. Uncorrected distortion at full telephoto is 0.4% pincushion, so the in-camera JPEG was overcorrected slightly. Canon's bundled Digital Photo Professional and Adobe Camera Raw automatically reduce geometric distortion, producing distortion measurements similar to in-camera JPEGs.

High distortion is quite common at wide angle in smaller lenses these days, and most RAW converters will automatically correct for it. There is however going to be a loss of resolution as well as possible interpolation artifacts as a result of such strong correction, because pixels near the corners of the frame are being "stretched" to correct for the distortion. And in the case of the G5X, the image circle does not cover the entire sensor at wide angle (we also saw this with the Canon G7X and G1X II), requiring even more interpolation back to full 20-megapixel image dimensions. If you look closely at the corners in the G5X's wide-angle JPEGs, they are soft and detail is a little rough with straight edges in the resolution target looking jagged. 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 fairly low at wide angle, and lower at telephoto in JPEGs. Mild to moderate blurring in the corners of the frame at wide angle and at full telephoto, though telephoto improves stopped-down.

Chromatic Aberration. Lateral chromatic aberration is fairly low in the corners at wide angle, and there's very little CA in the center. At full telephoto, lateral chromatic aberration is also low in the corners and the center. See below for 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 G5X's lens produces moderately soft corners at full wide angle when wide open. Blurring is roughly the same in all for corners from our sample, with the lower right perhaps just a touch softer than the rest, but softness doesn't extend very far into the frame and the center is quite sharp. Rough edges and much of the softness are due to the strong geometric distortion and CA correction taking place at wide angle. At full telephoto the bottom right corner is the softest when wide open, with the other corners a little sharper though not as contrasty as the center, and the center is not quite as sharp as at wide angle.

Corner Shading. Vignetting is fairly low at either end of the zoom, even wide open. (Apologies for the slightly blue tint in the corner crops. That's our fault and not the camera's, as our studio lights on the right side were a little too cool.)

F5.6. When the lens is stopped-down to f/5.6, corner sharpness actually degraded a bit at wide angle, with lower contrast, while the center remained quite sharp. At full telephoto, corner sharpness and contrast improved dramatically, while sharpness in the center improved just slightly. Vignetting is not apparent at either end of the zoom range. (Again, apologies for the unbalanced lamp temperatures.)

Chromatic Aberration Correction

Not surprisingly, chromatic aberrations are much higher in uncorrected RAW files than in camera JPEGs. As you can see, the Canon G5X's DIGIC 6 image processor does a pretty good job suppressing most of the chromatic aberration in JPEGs (crops on the left) versus RAW files converted in RawDigger (on the right), which does not correct for C.A. Note that most commercial converters like Adobe Camera Raw will automatically correct for C.A, as the G5X's .CR2 RAW files have a built-in lens profile.

When we reviewed the Canon G7X (and G1X II), we noticed its lens produced what looked like localized flare that can also be described as a glowing softness or a halo effect that is sometimes accompanied by axial chromatic aberration. The defect was most noticeable in high-contrast subjects that were slightly outside and usually behind the plane of focus, and diminished as you stopped down. The aberration appeared to be worst-case at wide angle and closest focus, however, we also saw it in shots at more normal subject distances, and at other focal lengths.

We didn't specifically test for this with the G5X but since it uses the same lens, it is something to watch out for. You may want to stop down a click or two to avoid or reduce this effect when shooting close distances, particularly for high-contrast or bright subjects that have some depth to them. Of course, having to stop down unfortunately negates the value of a fast lens in some circumstances.

Coverage
Excellent accuracy from the electronic viewfinder and LCD monitor.

The Canon PowerShot G5X's electronic viewfinder and LCD monitor both displayed excellent accuracy in record mode, showing essentially 100% coverage at wide angle and at full telephoto.