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Canon PowerShot A50 Canon's "Digital ELPHs" goes megapixel plus - great picture quality, superb portability! Select a topic Reference: Datasheet PowerShot A50 Test Images --------------------------------- 1. Intro and Highlights 2. Executive Overview 3. Design 4. Viewfinder 5. Optics 6. Exposure & Flash 7. Shutter Lag & Cycle Time Tests 8. Operation & User Interface 9. Camera Modes & Menus 10. Image Storage & Interface 11. Video, Power, Software 12. Test Results & Conclusion --------------------------------- Print-Friendly Review Version Additional Resources and Other Links Reader Comments on PowerShot A50 Review --------------------------------- Digital Camera Comparometer (TM) --------------------------------- <-- Digital Cameras (Home) <-- Digital Camera Reviews Index <<Viewfinder :(Previous) | (Next): Exposure & Flash>> Page 5:Optics Review First Posted: 7/10/1999

Optics
The PowerShot A50's lens is a true optical zoom, with a focal length range equivalent to that of a 28-70mm lens on a 35mm film camera. This is a bit wider than the lenses on most digicams, meaning that it won't get you quite as close to your subjects as some other cameras, but will do a better job of fitting everything into the frame in tight quarters. (Combined with an excellent low-light capability, this suggests that the A50 would be an ideal choice if a lot of your shooting is done indoors.) As part of its excellent low-light performance, the lens is a fairly "fast" one, having a maximum aperture of f/2.6 at wide-angle, and f/4.0 in telephoto mode. The lens is an autofocus design, with a normal focusing range of 20 inches (51 cm) to infinity, and a range in the separate macro mode of 6.7 to 20 inches (17 to 51 cm). The zoom position is controlled by a rocker control in the upper left-hand corner of the camera's rear panel.
The PowerShot A50's zoom control achieves a good balance between speed and "settability", apparently allowing the focal length to be set continuously anywhere within the lens' range. We haven't been tracking this, but some cameras afford less-smooth control over lens focal length, seeming to prefer a relative small number of discrete steps, rather than a continuous range. The A50's lens seems to allow a continuous range of settings, but does have a slight "backlash" at the wide and telephoto ends, depending on the direction you're zooming in: If you're moving from telephoto toward wide-angle focal lengths, the lens will "back up" a tiny amount after you've released the zoom control, while the lens is in the telephoto half of its range. (Once you get into wide-angle territory, this behavior disappears.) Likewise, as you move from wide to telephoto focal lengths, there's a similar "backlash" while you're in the wide-angle range. Overall, this effect is much less severe than we've seen in some cameras, but it does make (very) precise framing with the zoom a bit more difficult. We don't see this as a huge problem though, particularly when adjusting your shooting position by as little as a foot or so will compensate for any hesitation in the zoom mechanism.
In keeping with Canon's long experience and reputation for optical quality in the film camera world, the lens on the A50 appears to be of very high quality. Chromatic aberration (seen as a color "fringing" on high-contrast objects near the edges of the field of view) is virtually non-existent. Geometric distortion is also fairly low, ranging from 1.1% barrel distortion at the wide-angle end of the lens' range to no measurable distortion (either barrel or pincushion) at the telephoto end. (While we only measure geometric distortion at the end of the lenses' range, an informal test seemed to show that the barrel distortion vanished fairly rapidly as we moved away from the widest-angle setting of the lens.)
Autofocus-Assist Light
We gave this feature it's own heading, because low-light focusing has become such an issue with digicams lately. Cameras with through-the-lens contrast-detect autofocus systems (which generally produce the most accurate results with good lighting) have a hard time finding the optimum focus when the scene lighting is low. A very few cameras (the PowerShot A50 being one) provide a focus-assist light when there's not enough ambient light available to focus with. In the case of the A50, this light is provided by a small incandescent bulb internal to the camera, which casts a pattern of light and dark vertical bars onto the subject when the light level is less than ~EV 10 or 11. This lets the camera focus accurately in complete darkness, a very nice feature. (The one possible downside is that it would prevent truly candid shots under low light. For our part though, we'll take well-focused non-candids any day!) This autofocus-assist worked very well, as even shots taken in the very darkest of settings were perfectly focused.