Testing / Performance
*To evaluate the color reproduction capabilities of the Pentax Optio S55, we recorded a series of exposures of an industry standard GretagMacbeth color chart under optimum lighting conditions. We uploaded the images to Imatest Imaging Software to determine the accuracy of the S55’s rendered tones. Oftentimes camera manufacturers will purposely enhance certain sections of the color spectrum in an attempt to produce images with more vivid palettes. Although these "enhancements" may make landscapes and portraits appear more vibrant, these purposeful over-saturations are considered inaccurate by Imatest and will harm the overall color score eventually assigned to the camera. This is because users can easily embellish tones following capture; however, replicating the natural scene in software is a difficult task.
In the chart below, for each color tile, the colors produced by the Optio S55 are displayed in the outer square, while the corresponding ideal is placed in the vertical rectangle. The small square in the center of each tile is a color-corrected version as might be attained by a software application.
In the chart displayed below, the same color testing results are again represented, in a more quantitative manner. The colors placed within the circles represent the tonal ideal, while the corresponding squares are the camera’s produced tones. The longer the line connecting the two shapes, the less accurate the camera’s reproduction of that tone.
The Pentax Optio S55 had difficulty reproducing accurate tones, rendering colors that were highly over-saturated and inaccurate. The camera earned a 6.62 overall color score based on the strong variance between the camera’s produced colors and the corresponding ideal. This will be a problem for users seeking a well represented reproduction of the scene straight from the camera. This is a major problem for an entry-level camera, requiring point-and-shoot users to invest large amounts of time post-capture adjusting the color on a software application. Therefore, users who are intent on image quality should expect the S55 to be more of a point-shoot-and-edit camera. By comparison, the Olympus D-425, a sub $200 (USD) camera, earned an overall color score of 8.42 and would be a stronger contender for this audience if color reproduction is more of a priority than a large LCD screen.
**Still Life Scene **
Below is a shot of our inspired still life scene photographed with the Pentax Optio S55.
Note: This image was shot under nearly 500 lux of illumination - which is an immense amount of light. This should not have been a dark exposure! At ISO 50, the S55 selected an aperture setting of f/3.5 and 1/60 shutter speed. The white balance was set manually.
Resolution / Sharpness*(2.78)
*To evaluate the resolution of the Pentax Optio S55, we recorded a series of exposures of an industry standard resolution chart and imported the files into Imatest Imaging Software. The software reads the images and indicates the number of actual number of pixels used in composing the photo. We contrast the detected pixels with the advertised effective pixel count and report the score as both a percentage and actual pixel count. When this is done, cameras that earn a percentage score exceeding 70% of their advertised resolution are deemed "good" performers, while anything over 80% is "very good," and anything beyond 90% is "excellent."
The Pentax Optio S55 contains a 1/2.5-inch 5 MP CCD and 3x optical SMC Pentax power zoom lens formed of 6 elements in 5 groups with 2 dual-sided aspherical elements. Our resolution tests concluded the camera only utilizes 2.78 actual megapixels for imaging. This is just 57% of the advertised count and places the camera far below most similarly styled cameras we have tested. Users should expect strong limitations when cropping or enlarging photos and will be limited in print size. 4 x 6 sized prints should not display visible pixilation; however, when pushed to 8 x 10-inch prints, there will be a noticeable reduction in quality.
Noise - Auto ISO*(4.95)
*For cameras that offer manually selectable ISO settings, we test the amount of noise produced at each ISO setting as well as in auto ISO mode. Using the Optio S55’s auto ISO setting, in bright lighting conditions, the camera produced images that contained a marginal degree of visible noise, but still remained reasonably clean. The camera earned a 4.95 overall score in auto ISO mode, which is respectable among other similarly priced cameras within the sub-$300 or sub-$250 price range.
Noise - Manual ISO*(6.46)
*When testing the camera’s noise suppression capabilities using its manually selectable ISO settings, we capture a series of shots of our GretagMacbeth color chart under bright, controlled lighting conditions at each available ISO rating and import the results into a regression analysis to calculate an overall score. The results are displayed in the graph below, with the camera’s ISO ratings placed along the horizontal x-axis, and the resulting noise plotted on the vertical axis.
With manual ISO ratings of 50, 100, 200, and 400, the Pentax Optio S55 achieved a 6.46 overall noise score, which is an improvement over the auto mode rating. Users of the Optio S55 will find that the camera’s 50 and 100 ISO ratings handle noise well, producing crisp images with little noise; however, once pushed to the 200 and 400 settings, the noise is drastically increased. The two higher settings will remain usable, but image quality will be substandard and in many cases (as long as it’s not a night skyline), it might be wiser to rely on the flash.
Low Light Performance*(3.0)
*To perceive the low light capabilities of each camera we review, we capture a sequence of images at the camera’s highest offered ISO setting, without the assistance of the flash, to isolate the sensitivity of the imager. The tests are shot at decreasing light values of 60, 30, 15, and 5 lux to replicate common low light shooting conditions; 60 lux is comparable to a partially lit interior scene following dusk, while 30 lux is similar to a situation being illuminated by a 40 watt light bulb. Scenes being captured at 15 and 5 lux display the camera’s ability to capture an exposure in near darkness.
*Click on any of the above chart for additional image analysis *
Not surprisingly, the Optio S55 did not perform well in low light conditions. At 60 lux, the recorded images were filled with noise and the rendered colors were muddy, lacking vibrancy. Dropping to 30 lux, the resulting photos decreased in visibility and color reproduction and were virtually unusable, although objects were still moderately perceivable. Images garnered at 15 and 5 lux with the Optio S55 contained minimal to no information and barely deserve to be considered a photograph.
**Speed / Timing **
*Startup to First Shot (5.55) *
From the time the Pentax Optio S55 first starts up to recording a shot, nearly 5 seconds elapse. With a 4.45 second wait, be prepared to lose those classic photographs of your first born and their first steps since they’ll be already running by the time the camera gets going.
*Shot to Shot Time (8.08) *
The shot to shot times of the Optio S55 were in line with the camera’s glacial startup rate, capturing a shot every 1.92 seconds. The camera contains a continuous shooting mode (not deserving of the "burst" label) which will continue as long as the shutter is held, but does not do anything to improve the camera’s sluggish speed. While most point-and-shoot users will not be taking many rapid-fire sequences, many point-and-shoot cameras now are marketed with burst rates of 2, 2.5, or 3 frames per second, making this camera seem a bit leisurely by comparison.
*Shutter to Shot Time (7.89)
*In terms of shutter lag, the Pentax Optio S55 put up another less than stellar performance, requiring 0.51 seconds from the time the shutter is depressed to capture. This delay shouldn’t be a huge issue for static portraits but may become problematic in low light situations or when moving subjects are encountered. Hopefully Optio S55 users will have a steady hand.