Canon G7X Optics

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

The Canon PowerShot G7 X's 4.2x zoom lens covers the equivalent of about 24-100mm on a 35mm camera, offering a more generous zoom ratio than most cameras in its class. 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 somewhat soft, likely because of the strong distortion correction applied (see below). Little chromatic aberration is visible as it is effectively suppressed in JPEGs, though some minor 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 good sharpness and contrast across the frame. Again, chromatic aberration is negligible because the G7 X suppresses it in JPEGs, though we have seen some significant purple or red fringing around strongly backlit subjects in some shots.

The G7 X also offers digital zoom up to 4x, and what Canon calls a "digital teleconverter" at preset magnifications of 1.6x and 2.0x, however we did not test those modes.

Overall, very good far-field performance at f/5.6 at medium to telephoto focal lengths, but the lens does not perform that well in the corners at maximum wide angle. See below for more.

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 G7 X's lens captured a larger-than-average minimum area of 3.26 x 2.18 inches (83 x 55 millimeters). 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 G7 X's built-in flash is partially blocked by the lens at closest focus distance, resulting in a very dark shadow in the bottom right and overexposure in the top left. You'll likely want to use external lighting for close macro shots with the G7 X.

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

JPEG: The Canon G7 X's just under 0.3% 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 4.8%. 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 0.3% 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 in the corners of the frame are being "stretched" to correct for the distortion. And in the case of the G7X, the image circle does not cover the entire sensor at wide angle (we also saw this with the Canon G1X II), requiring even more interpolation back to full 20-megapixel image dimensions. If you look closely at the corners in the G7 X'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 low to moderate at wide angle, and lower at telephoto in JPEGs. Mild to moderate blurring in the corners of the frame at wide angle, but good corner sharpness at full telephoto.

Chromatic Aberration. Lateral chromatic aberration is moderate in the corners at wide angle, but not very bright and there's very little CA in the center. At full telephoto, lateral chromatic aberration is moderately low in the corners, but some axial chromatic aberration can be seen in the center, though it's fairly low. We have however seen some relatively bright purple or red fringing around bright objects in real-world shots. 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 G7 X's lens produces moderately soft corners at full wide angle when wide open. Blurring is about the same in all for corners, but softness doesn't extend very far into the frame though there is some loss of definition, but 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. Corners at full telephoto are fairly sharp but not as contrasty as the center with clear signs of CA suppression, 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.

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 especially contrast improved, while sharpness in the center remained about the same. And vignetting is not apparent at either end of the zoom range.

Chromatic Aberration Correction

Not surprisingly, chromatic aberrations are much higher in uncorrected RAW files than in camera JPEGs. As you can see, the Canon G7 X'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 G7 X's .CR2 RAW files have a built-in lens profile.

When we reviewed the Canon 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.

As you can see from the above crops, the G7X's lens also seems to exhibit a similar trait, although perhaps not quite as severe as the G1X II's. We haven't fully characterized at what apertures, focal lengths and focus distances this issue appears, but as you can see, it happens at both wide angle and telephoto when wide open (left crops), as well as at macro and non-macro distances, though it diminishes with distance. 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
Very good accuracy from the LCD monitor.

The Canon PowerShot G7 X's LCD monitor displayed very good accuracy in record mode, showing just over 100% coverage at wide angle, and close to 101% coverage at full telephoto.