Canon PowerShot A640

Reviewed April 2007

Image Quality

Since its inception, Canon's A-series cameras have been designed to be economical, but nevertheless offer a high image quality. The PowerShot A640 continues in the same vein.

The optics of the A640 are the same as those of the very successful and highly regarded A620, and are just as well suited to the 10-megapixel CCD of the A640 as they were to the 7 megapixel CCD of the A620, a fact that in and of itself speaks very well for the resolving power of the lens.

The 4X zoom marches through its entire focal length in 8 steps, but transits from wide angle to telephoto or vice versa in just over 2 seconds when the zoom control is pushed to its stops and held there. Indeed, the A640 is generally quick, whether when starting up or when capturing an image.

The zoom's range, which is equivalent to a 35 to 140 mm, is well-suited to most everyday photography, and avoids the long telephoto range that usually leads to camera shake unless the camera is equipped with a stabilizer.

High resolution sensors of compact cameras such as the A640's 10-megapixel CCD, tend to get noisy quickly at higher ISO values. Somehow the A640 avoids that fate until its upper limit of 800 ISO, and even then, if the image size is reduced at printing time, for instance 6 x 4 inch (10 x 15 cm) instead of the maximum that a 10-megapixel image can yield at 300 dpi, 12 x 9 inches (30 x 23 cm), the quality remains quite high.

At lower ISO settings, such as 80 and 100, images contain either no noise or very little, as is the case for 200 ISO. The 400 ISO setting is noisier, but still quite useable, and can be very useful when the ambient light is poor.

The A640 also offers a wide range of image sizes, including a 16:9 aspect ratio that takes full advantage of the entire width of the CCD to produce an image with an aspect ratio that is proportional to HDTV (3648 x 2048), unlike many other cameras' 16:9 aspect formats that limit the resolution to the maximum of HDTV (1920 x 1080), allowing the image to be used in another context, such as printing, and not just viewing on a TV.

This ample range of formats is combined with a choice of 3 compression levels, at all image sizes with one exception, the Postcard format, which can be used to stamp images with the date and time (often a bad idea since it is permanent and all digital images contain the shot date and time in the EXIF data, which can be used to make prints with the time and date).

Set to the highest image quality, Superfine, the A640 produces images that show no sign of the compression, and which are filled with detail, albeit a touch less when captured at the wide angle end than elsewhere in the focal length range of the zoom.

Similarly, the default Evaluative metering handles most subjects perfectly, including backlit subjects, where it ensures that the darker parts of the scene are well exposed, even if occasionally the highlights are slightly clipped.

Many of the features of the A640 are devised so that it is appropriate for a wide variety of users: the A640 provides a simple to use point-and-shoot Auto mode, perfect for a novice; a large number of scene modes that can meet the needs of an intermediate user; and the Creative Zone modes — program, aperture priority, shutter priority and manual — are what most advanced users will want.

With a 10-megapixel CCD, the A640 offers a high resolution image that is able to capture a superb level of detail and which guarantees great prints. And this, combined with a broad set of modes that allow a photographer to grow, make it one of the best compacts on the market today.