Canon PowerShot G12 The Lens and Focal Lengths


The technology and engineering that goes into your camera is a marvel, but it isn’t worth a darn if it can’t get the light from outside onto the sensor. The G12 includes one built-in lens capable of a multitude of tasks, from focusing on a subject, to metering a scene, to delivering and focusing the light onto the camera sensor.

For most people, however, the first consideration of a lens is its focal length, more commonly referred to as zoom.

A wide angle lets you include a large scene in the frame (Figure 2.3). It can display a large depth of field, which allows you to keep the foreground and background in sharp focus, making it very useful for landscape photography. It also works well in tight spaces, such as indoors, where there isn’t much elbow room available (Figure 2.4).

The 6.1mm zoom setting provides a wide view of the scene but little detail of distant objects. [Photo: Jeff Carlson]

When shooting in tight spaces, such as indoors, a nice wide-angle lens helps capture more of the scene. The photographer also used a third-party wide-angle attachment to further increase the field of view. [Photo: Anneliese Voigt]

The lens in your camera is capable of shooting photos at 6.1mm at the wide-angle end, and up to 30.5mm when at its full telephoto (zoomed) end; Canon’s marketing materials refer to the level of zoom, which is 5x.

35mm Equivalent Focal Lengths

In digital photography, you’ll often see focal lengths expressed as “35mm equivalent.” The G12 shoots a 35mm equivalent range of 28mm to 140mm—but what does that mean? Without wading into the field of optics, here’s a simplified explanation. Traditionally, a photo exposed on film using a 35mm lens delivered a “normal” image, which was close to what your eye perceives. The image sensors in most digital cameras are physically smaller than the frame of film exposed in old cameras, so the area of data recorded by a digital camera is smaller than the area of light that the lens is actually seeing. This narrower field of view creates the same effect as zooming in, which is sometimes referred as the crop factor. The crop factor for the G12 is roughly 4.6: the 6.1mm view is about what you’d see if you used a 28mm lens on a film camera (6.1 x 4.6 = 28.06).

The middle range of the zoom (Figure 2.5) is useful for photographing people and architecture, and for most other general photographic needs (Figure 2.6).

The middle of the zoom range gets you closer to your subject. Compare this to Figure 2.3, shot from the same location. [Photo: Jeff Carlson]

The middle range of the zoom worked well in this image. [Photo: Lynette Coates]

The upper part of the focal length range is referred to as telephoto. You can zoom in and get more detail on distant objects, but the angle of view is greatly reduced (Figure 2.7). A tight zoom dramatically focuses your attention, however (Figure 2.8).

You will also find that you can achieve a much narrower depth of field. However, you may also notice something called distance compression, which means objects at different distances appear to be much closer together than they really are.

One sacrifice that is made when shooting telephoto is in aperture. When zoomed all the way in, the lens is capable of a minimum aperture of f/4.5 (compared to f/2.8 at the wide angle), which is the middle of the camera’s possible aperture range. That means it cannot work in lower light levels without the assistance of image stabilization, a tripod, or higher ISO settings.

Using the Zoom Control

  1. With the camera on in any of the shooting modes, press the Zoom lever to the right (clockwise) to zoom in (telephoto). Press the lever to the left (counterclockwise) to zoom out.
  2. Use the lever to fine-tune the amount of zoom you want.

30.5mm is the G12’s highest optical zoom. This shot was taken from the same vantage point as Figure 2.3. [Photo: Jeff Carlson]

The camera’s maximum tele- photo highlights the vibrant colors of the Chin Swee Temple against the dark and cloudy sky. [Photo: Thomas Baake]

Digita l Zoom

The G12 is capable of a 20x zoom, or an impressive 560mm! However, there’s a catch: any focal length above 140mm on these cameras is accomplished by using digital zoom. The camera’s processor makes a sophisticated guess about how to enlarge the scene to appear zoomed-in. To accommodate for the lack of optical information, the processor interpolates the difference by filling in pixels.

In the past, my gut reaction would have been: “Turn it off now!” After all, I presume your aim in purchasing a G12 is to create great shots, not ones that are fuzzy due to interpolation. But, at the risk of having my photographic license revoked, I have to say that the digitally zoomed images on these cameras are…not bad. I wouldn’t rely on the feature all the time, but if the choice is to get the shot with digital zoom or not get a shot at all, then the result can be acceptable (Figure 2.9).

Digital zoom lets you get even closer to the subject, but at the expense of some sharpness. The detail at right is reproduced at 100% its original size. [Photo: Jeff Carlson]

Enabling Digita l Zoom

  1. Press the Menu button and make sure you’re viewing the shooting menu.
  2. Press the Down button or rotate the Control dial to highlight the Digital Zoom option. (Note that the option is inaccessible if you’re shooting in RAW or at an aspect ratio other than 3:4.)
  3. Press the Left or Right button to choose one of the following three options:
    1. Standard: This option enables digital zoom to get telephoto shots that are closer than the optical zoom.
    2. 1.4x: Instead of switching from optical to digital zoom, the camera applies a “digital tele-converter” to the entire zoom range. The image is magnified 1.4 times normal, and “1.4x” appears onscreen.
    3. 2.3x: The image is magnified 2.3 times normal using the digital tele-converter and “2.3x” appears onscreen.
  4. Press the Menu button to apply the change.

The camera also incorporates what Canon calls Safety Zoom: If you’re shooting at a smaller JPEG image size, the amount of image deterioration due to interpolation isn’t noticeable. For example, you can get a clean image at 11x zoom when shooting at the M2 size (1600 x 1200 pixels). The zoom indicator or digital tele-converter number changes from white to blue to indicate that you’ll see image deterioration; within the Safety Zoom range, the number becomes yellow.

Since I still prefer optical zoom over digital zoom, here are the steps to turn off the feature. In most cases, zoom with your feet instead: get physically closer to the subject.

Turning off Digita l Zoom

  1. Press the Menu button and make sure you’re viewing the shooting menu.
  2. Press the Down button or rotate the Control dial to highlight the Digital Zoom option.
  3. Press the Right or Left button until Off is visible.
  4. Press the Menu button to accept the setting.