Canon PowerShot A20Canon's "value priced" 2 megapixel camera has 3x zoom, takes great pictures!<<Viewfinder :(Previous) | (Next): Exposure & Flash>> Page 5:OpticsReview First Posted: 5/10/2001 |
OpticsThe PowerShot A20 features a high-quality Canon 3x, 5.4-16.2mm zoom lens that is equivalent to a 35-105mm lens on a 35mm camera. The maximum aperture setting is f/2.8 at the wide-angle setting and f/4.8 at the maximum telephoto range. Aperture settings and shutter speeds are automatically controlled, with no settings reported on the LCD display. Focus ranges from 2.5 feet (76 cm) to infinity in normal mode. In Macro mode, focus extends from 6.3 inches to 2.5 feet (16 to 76 cm) with the lens at wide angle, and from 10.2 inches to 2.5 feet (26 to 76 cm) with the lens at telephoto. Focus is automatically determined via a through-the-lens, three-point AiAF (Artificial Intelligence Auto Focus) system, which gauges focus from three areas in the center of the frame. The Macro / Infinity button on the back of the camera not only places the camera in Macro or Normal focus modes, but also accesses an Infinity focus mode in Manual mode, which is good for shooting fast-moving subjects from a distance. This setting decreases shooting time, as you don't have to wait for the camera to set focus.
The A20's built-in flash doubles as an autofocus (AF) assist light, which is automatically activated whenever the camera is focusing in low-light situations (though we sometimes noticed it operating in fairly well-lit shooting situations). The AF assist light emits a dull, orange light that falls on the central portion of the subject, providing additional light for more accurate focusing. We found that the AF assist worked very well, as we obtained clearly focused images in our low-light testing, even at the lowest light level. The A20 doesn't offer an adjustable focus lock, but you can manually lock focus for a specific area of the image by simply framing the portion of the subject you want in focus in the center of the frame, halfway pressing the Shutter button, recomposing the shot while holding down the Shutter button halfway, and firing the shutter.
Though the A20 lens does not feature filter threads for attaching accessory lenses, Canon does offer a wide-angle and close-up lens converter kit, which attaches to the camera via a small adapter. The adapter connects to the inside of a small ring at the base of the lens. The ring features a series of small grip notches, which allow it to be loosened and removed by the Lens Adapter Dust Cap, creating a space for the adapter to attach. The adapter supplies a set of 52mm threads to attach filters or lenses.
In addition to the 3x optical zoom, the A20 also offers a 7.5x digital telephoto (combined optical and digital), which is not available in Stitch-Assist mode. Digital zoom is automatically enabled by zooming past the optical zoom range whenever the LCD monitor is active. The amount of digital zoom is reported on the LCD display, in blue numbers on the right side of the screen. Keep in mind that digital zoom decreases image resolution, and often increases noise levels. In our testing, we noticed that the A20's digital telephoto did a fairly good job of maintaining detail. Resolution was decreased and details softened somewhat, but the A20's digital zoom performed better than many we've seen.
Optical distortion on the A20 is moderate at the wide-angle end, as we measured a 0.57 percent barrel distortion. The telephoto end fared much better, as we couldn't even find one pixel of pincushion distortion. (We actually noticed about a half-pixel of barrel distortion, which is fairly insignificant.) Chromatic aberration is also very low, showing only a half-pixel of coloration on either side of the black target lines. (This distortion is visible as a very slight colored fringe around the objects at the edges of the field of view on the resolution target.)
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