The G15's feature set, design and operation is very close to its predecessor G12 but there are some key differences. The G15 has a faster lens, a higher resolution movie mode and offers ISO 6400 and 12800 at full resolution. On this page we will concentrate on examining these new features but we have also included some features that were available on the G12, such as Raw shooting, in-camera HDR and digital filters.

Fast lens

With the launch of the G15, Canon has added-back one of the original characteristics of the G-series; a fast zoom lens. It covers the same 28-140mm equivalent focal length range as the G12's, but is a stop and a third faster, at F1.8-2.8 rather than F2.8-4.5. As we mentioned in the introduction to this review, this should give the G15 a distinct advantage over its predecessor in poor light since the G15's faster lens means that at any given light level you can keep the ISO at a lower setting, capturing better image quality with more detail.

The different sensor sizes of the cameras in this class make it difficult to directly compare their lenses. The graph below shows the equivalent apertures* of each camera available at each equivalent focal length. This makes it easy to visualize the lens ranges of the cameras and also means you can see which camera will offer shallowest depth-of-field at any given focal length.

Both scales are logarithmic, so that a one-stop change of aperture brightness is a consistent height and that a doubling of focal length is always represented by the same width along the bottom on the graph. As you can see, the G15 consistently offers an aperture 1 stop brighter than the G12 across its entire focal length range.

Focal length 28-30mm 31-41mm 42-60mm 61-96mm 97-140mm
Maximum aperture F1.8 F2 F2.2 F2.5 F2.8

The extra brightness is not only helpful in low light though - it should also allow you to get better subject/background separation when shooting towards the tele end of the zoom - especially useful for portraits.

The table below compares the G15's and G12's lens specifications. Along with the familiar 35mm-equivalent focal length, we've also included a 35mm-equivalent aperture range, which gives some idea of the relative control over depth of field offered by the two cameras' lenses.

  Sensor area, mm2
Focal length range Focal length range (equiv.) Aperture range Aperture range (equiv)*
Canon PowerShot G15 41
6.1-30.5mm 28-140mm F1.8-2.8 F8.3-12.9
Canon PowerShot G12 41
6.1-30.5mm 28-140mm F2.8-4.5 F13-20.9

* Equivalent aperture, in 135 film terms - this gives an idea of the depth of field control offered by the lenses when the sensor size is taken into account.

G15, ISO 80, 140mm equiv., F2.8 G12, ISO 80, 140mm equiv., F4.5
100% crop 100% crop

Photographers tend to be interested in how well a lens can blur backgrounds when shooting portraits at full telephoto, and in this respect the G15 does very well for a compact, due to its combination of a relatively fast aperture and long-ish lens. The samples above were shot at the long end of the lens and maximum aperture. As you can see the G15 blurs the background behind the subject quite well, but the difference between G15 and G12 with its F4.5 maximum aperture at the long end of the lens is relatively subtle.

The low light advantage

The G15's maximum aperture of F2.8 at the long end of its zoom gives it a real advantage over its predecessor, and indeed competitive cameras in poor light. In effect, it gives you a 1, 1/3 'stop' benefit compared to the G12, which could be the difference between a sharp picture or a blurry one. Or between a noisy image and one taken at a lower, cleaner ISO sensitivity setting.

In this example we set up a portrait in very low-intensity tungsten lighting, and shot our subject at the furthest extent of the G12 and G15's zooms - 140mm equivalent in both cases. We shot handheld, in program mode with Auto ISO selected. These samples should show us how the cameras compare in a tough environment, where every last photon counts.

We shot this portrait on both the Canon PowerShot G12 and G15, under very low intensity tungsten light. We shot hand-held, with image stabilization turned on.
Canon G12 @ 140mm, hand-held, IS On. Canon G15 @ 140mm, hand-held, IS On.
Auto ISO (1600), F4.5, 1/8sec (100% Crop) Auto ISO (1600), F2.8, 1/20sec (100% crop)

The G12 and G15's automatic ISO sensitivity functions are limited to a maximum ISO of 1600, which both cameras have selected here. So with ISO fixed at 1600, and maximum aperture fixed at F4.5 and F2.8 respectively, the only variable is shutter speed. As you can see, the G12 has had to select a low shutter speed of an eighth of a second, and although its image stabilization system has done very well, the final result is a blurred image - it is likely that slight subject movement played a part as well. The G15 has the advantage of that faster F2.8 lens, and has been able to select a correspondingly higher shutter speed of 1/20sec - still not high, but high enough that camera shake has been successfully minimized thanks to the camera's optical image stabilization system.

To hit a 'safer' hand-holdable shutter speed we could have increased the G15's ISO sensitivity to ISO 3200, but to match this on the G12 would mean selecting ISO 6400, at which point resolution drops to 2.5MP (the G15 can still shoot at full-resolution all the way up to ISO 12,800). It's important to note that this example is extreme - we shot this under very low light indeed, and you hopefully shouldn't find yourself shooting at shutter speeds this low at the long end of the G15's zoom all that regularly. Or at least, if you do, you shouldn't expect miracles, certainly not in Auto ISO mode, with its rather nonsensical max ISO limitation of 1600...

RAW shooting

The Canon Powershot G15's ability to record Raw files allows you to modify many shooting and image parameters such as white balance, sharpening, noise reduction, and to a degree even exposure in post-processing. As you can see if you look at the full-size version of the sample shot below converting your Raw files in Adobe ACR 7.3. only gets you a minimal amount of additional detail, the G15's JPEGs simply show very good detail already.

However, Raw processing can still be very useful to recover highlight detail that has been lost in the out-of-camera JPEG. In our JPEG sample the sky has been 'blown out' and shows no detail at all. By pulling the Highlights slider in Adobe ACR 7.3 Beta all the way back we have been able to recover much of the blue sky and clouds, greatly improving the image.

ACR 7.3 Beta Raw

High ISO settings

While the G12 captured ISO 6400 and 12800 images in a special low-light mode, with very little manual control and at reduced image size, on the G15 these high ISO settings are now part of the standard sensitivity range and capture full-resolution images.

ISO 6400 ISO 12800
100% crop 100% crop

The image quality at these very ISO settings is surprisingly good with well-controlled chroma-noise. At the very highest setting the image gets pretty soft with a lot of noise reduction smearing and visible noise but at ISO 6400 illuminance noise is fine-grained, almost resembling film-grain, and the image shows decent high-contrast detail.

While noise and noise reduction artifacts are quite intrusive at these high ISO settings when viewing images at 100%, the G15's high ISO output is perfectly usable at smaller output sizes, further expanding the usability of Canon's G-series in low-light situations.

In-camera HDR

The G15's HDR mode works in the same way as the G12's, by combining three images, one of the 'correct' exposure plus one over-exposed image to capture shadow detail and an underexposed image for highlight detail that would otherwise be missing. These exposures are then sandwiched together in-camera to produce a single image. This is not intended to be a handheld mode. Because the camera is combining multiple shots, a tripod is essential to avoid ghosting in the final image, due to camera movement between frames. However, even with a tripod you might still see ghosting artifacts around any moving subjects that are present in the frame. Some other brands' HDR modes, for example Sony, auto-align the individual shots which removes the necessity to use a tripod. The same is true for Canon's latest DSLRs.

Standard JPEG
HDR Mode

HDR has become a common feature on high compact cameras over the last couple of generations or so and whilst not an essential function, it can be very useful in difficult high-contrast scenes. In the sample shot above shadow areas have been lifted, and the highlight areas held back slightly, which has successfully balanced the scene and avoided detail loss in either part of the image. Enthusiasts beware though - this is a fully automatic mode, so no control is possible over ISO, shutter speed or aperture or even AF area. You are also limited to color JPEG images only.

In-camera filters

The Powershot G15 comes with the same range of digital filter effects that we saw on the Canon G1 X. To access them you have to turn the mode dial to the filter position, at which point you lose most manual control over settings and the camera operates in full-auto mode. Once the dial is set to the filter position can you can select individual effects via the Func menu.

The HDR filter takes three frames in quick succession and merges them to an HDR image (tripod use is recommended to avoid ghosting), the rest of the filters are the usual digital effects that we've seen on a lot of cameras before. Most filters offer a degree of customization in terms of the intensity of the effect and some let you vary the color response.

The drawback of using these filters is that you cannot shoot raw and JPEG at the same time, so if you don't like the filter result, you don't have a Raw version of the image to try some alternative processing on. That said, they're still fun to play with and can create some interesting results with the right scene.

No filter
Color Accent
Toy Camera
Soft Focus
Super Vivid
Poster Effect

Some filters offer adjustment parameters, you can find more detail on the filters page of our Canon G1 X review.