Canon G3X Optics

Zoom
A very generous 25x zoom ratio, with good optical performance.

The Canon PowerShot G3X's 25x zoom lens covers the equivalent of about 24-600mm on a 35mm camera, offering a very generous and useful zoom range. Maximum aperture is a relatively fast f/2.8 at wide angle though that drops to f/5.6 at telephoto, already at about 170mm equivalent.

The following table reflects the maximum and minimum apertures as reported by the camera at various focal lengths:

Sharpness is quite good across most of the frame at full wide angle and f/5.6, but corners are touch 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 (~48mm 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 seem pretty good, with good sharpness and contrast across the frame, though this subject doesn't work well for evaluating the performance of long zooms. (This series is meant primarily to show zoom range -- see below for lab test shots.)

The G3X also offers digital zoom up to 4x, and what Canon calls "digital teleconverter" at preset magnifications of 1.6x and 2.0x available at any focal length. That means you may be able to shoot at a wider aperture than optically zooming to the equivalent focal length, should you prefer the extra light over the loss of detail inherent with all digital zooms. See above for an example of 2.0x digital teleconverter.

Macro
A larger than average macro area, with very good detail in the center. Flash worked well at full telephoto.

The Canon PowerShot G3X's lens captured a larger-than-average minimum macro area of 3.45 x 2.30 inches (88 x 58 millimeters), and the minimum focus distance at full telephoto (85cm) produces roughly the same magnification ratio as the minimum distance at wide angle (5cm). Sharpness is very good in the central area of the frame, though corners and edges are very soft from field curvature even at f/8. (Most cameras have some softening in the corners in macro mode, but usually not this much.) There's also some vignetting in extreme corners. The Canon G3X's built-in flash throttled down well at the telephoto end's closest focus distance, producing a slightly dim (with reflections likely impacted flash metering), but fairly evenly lit exposure though vignetting is even more noticeable. The G3X's large lens will probably interfere with the flash at wide angle though, likely casting a shadow at the closest distance.

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

JPEG: The Canon G3X's 0.2% barrel wide angle is very 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 G3X RAW files using dcraw (no corrections applied), we see that actual barrel distortion at wide angle is very high, at about 4%. 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 about 0.5% 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 small and/or fast 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 G3X, 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 G3X'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 in the corners of JPEGs. Mild to moderate blurring in the corners of the frame at both ends, but corners improve when stopped down.

Chromatic Aberration. Lateral chromatic aberration is moderately low 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 moderate in the corners, and low in the center. 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 G3X'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 are a little sharper but not as contrasty and they show some minor image doubling. The center wide-open at full telephoto is fairly sharp, but not as sharp as at wide angle.

Corner Shading. Vignetting is noticeable but reasonably low at either end of the zoom when wide open.

Stopped-down. When the lens is stopped-down to f/5.6 at wide angle, corner performance improves over wide-open, but they are still slightly soft. Performance in the center is very similar to wide-open. At full telephoto stopped-down to f/8, corner sharpness and contrast improve, while sharpness and contrast in the center also improve slightly, with diffraction limiting probably preventing further improvement. Vignetting is no longer 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 G3X'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 dcraw (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 G3X's .CR2 RAW files have a built-in lens profile.

Bottom line: Good overall optical performance for its type, and we're happy to report the lens doesn't seem to suffer from the localized flare issue we saw with the G7X and G1X Mark II.

Coverage
Excellent accuracy from the LCD monitor.

The Canon PowerShot G3X's LCD monitor displayed excellent accuracy in record mode, showing essentially 100% coverage at wide angle and at full telephoto, despite the heavy distortion correction at wide angle.