The Pentax Optio S55 doesn't allow much photographic control: you cannot manually adjust shutter speed or aperture. You can, however, adjust exposure compensation (plus or minus 2EV in 1/3EV increments) and bump sharpness, colour saturation and contrast up or down. You can also choose from three preset scene modes on the command dial or nine additional scenes in Picture mode. The camera has manual focus, but using the focus-range indicator is usually more effective than trying to determine focus through the monitor.
In 35mm-camera terms, the f/2.6-to-f/4.8 Pentax SMC 3x zoom lens has a range of 35.6mm to 107mm. Aimed at the point-and-shoot crowd, the S55 saves photos only in JPEG format. The movie mode produces 320x240-pixel, 15fps or 30fps AVI files with sound -- the capacity of your camera's SD/MMC card limits their size.
Useful extras include the Auto Select mode's help function, which explains settings and buttons. You can also choose from fun effects such as Pentax's colour-filter or black-and-white-plus-filter modes, accessible when shooting in Digital Effects mode or during playback, at which point you can apply the same effects -- or others -- to any photos you've taken.
The Pentax Optio S55 is no speed demon. After disabling the start-up screen, we clocked the camera's start-up time at 4.41 seconds. Shutter lag isn't usually an issue, though it can be noticeable depending on what you're shooting. It came in at 0.55 seconds in our tests. Shot-to-shot times are worse: 4.5 seconds without flash, 6.74 seconds with flash. Continuous shooting is remarkably slow and, on this camera, more about endurance than speed: you can keep shooting until your card fills up, but at the less-than-blistering pace of 0.5fps and 0.67fps. This is no action cam.
The 3x zoom is smooth and accurate, though not well suited to low-light conditions. Neither is the focus, as the S55 doesn't have an assist lamp. Autofocus can be sluggish in daylight conditions as well. We recommend switching from the default spot-focus setting to multi, as it improves responsiveness.
The S55's 64mm LCD provides plenty of space for composition and review, but it isn't very sharp or bright. It's sufficient for most uses, but bright sunlight can wash it out. The camera has no optical viewfinder.
Flash coverage is average for an ultracompact camera such as this, tending toward underexposure near the upper ends of its claimed range of 4.9m at wide angle and 2.8m at telephoto.
The Pentax Optio S55 produces satisfying, good-quality, but not wonderful images. A number of flaws emerged in our test shots. They were usually minor and not enough to ruin the photo, but they were noticeable nonetheless. First of all, the S55 is prone to slight underexposure and barrel distortion at the zoom's wide setting, as well as minor purple fringing in areas of strong contrast. Photos appear soft, on average, at the camera's default sharpness setting.
The S55 renders colours naturally in most instances and we saw good detail in our test shots. On the other hand, it has limited dynamic range, often blowing out highlights and showing limited detail in the shadows. The latter problem probably has something to do with Pentax's noise-reduction algorithm, which automatically kicks in for long or dimly lit exposures. It's effective at limiting noise across the ISO spectrum of 50 to 400, but in addition to reducing detail, it slows processing time.
The S55's movie mode produced clips of average, acceptable quality for the 320x240-pixel resolution offered.
Edited by Aimee Baldridge
Additional editing by Nick Hide