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Canon Powershot G11 Review

Lens and Resolution

The lens on the Canon Powershot G11 is a 6.1-30.5mm f2.8-f4.5 optically stabilized zoom. Well, its really more of a multi-focal length lens than a zoom because it has 14 different focal lengths spanning the range, but's that's the case with almost all digicams. The lens is the approximate equivalent in terms of field of view of a 28-140mm f2.8-f4.5 zoom on a full frame 35mm camera. Because of diffraction limitations associated with the use of a small sensor and small pixels, the minimum aperture the lens can be set to is f8. If smaller apertures were allowed, image quality would suffer.

Optical tests showed that the lens performance was very good. At all focal lengths it was sharp in the center and just about equally sharp at the edges and in the corners, even wide open. An example of center and edge resolution is shown below (100% crops):

As you can see, the center and corner of the frame show very similar resolution, and that resolution is high. It's comparable to a 10MP DSLR like the EOS 40D with a good lens. Stopping the lens down on the G11 doesn't actually result in higher image quality. In fact stopping down actually lowers the resolution slightly because diffraction effects start to come into play as mentioned above.

Canon Powershot G11 at wide (28mm) setting. 100% crops showing resolution vs. aperture

The above image shows 100% crops from the center of the image shot at 28mm, ISO 100 and four different apertures. While all are sharp, if you look closely you can see a slight drop in sharpness as the lens is stopped down each time.

Both vignetting and chromatic aberration are well controlled, though there is a little CA visible at wide and medium focal lengths (see image below). Though very little correction for these aberrations is needed, it is available via DPP if you shoot RAW files.

The above are cropped from 200% blowups of the G11 images in order to better show the small amount of CA present. At the widest setting there is a small amount of magenta/green fringing, at mid focal lengths this shifts to red/cyan and at the longest setting it's hard to see any CA at all. These crops are taken from the extreme corner of the images, where CA is expected to be at its worst.

The only significant aberration is rather visible barrel distortion at the widest setting. Again this can be corrected fairly easily, either in DPP if you shoot in RAW or in most image editors if you shoot in JPEG.

At mid and long focal lengths distortion is negligible.

Below is a 100% crop from the corner of the image (as shown in the inset), shot at 140mm focal length and ISO 800. As you can see, sharpness is excellent and chromatic aberration is not visible.

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