Pentax K100D Digital Camera Review

DigitalCameraInfo tests a camera's color accuracy with a standardized procedure under tungsten lights in our lab. The more accurate a camera’s color reproduction, the better it does on our test. Some cameras lose points for accuracy because the manufacturers purposefully boost colors to produce vivid effects. Our position is that accurate results are preferable because color can be intensified in printing or presentation. It's much harder to get back to accurate colors from the tarted-up kind.

 

We shoot a standard GretagMacBeth color target which has 24 squares of color on it. We use Imatest software, the industry's best program for evaluating image quality and camera accuracy, to analyze the images we take. Imatest produces results for saturation and color error. Saturation indicates whether the colors are washed out or too bright. Color error indicates if individual colors have the wrong hue. 

The chart below shows a GretagMacBeth chart captured with the Pentax K100D that has been modified by Imatest to illustrate the color error. The big squares are the colors as the K100D shot them, the middle squares are the ideal colors, and the vertical rectangles show the ideal tones corrected for luminance.

The second chart shows the K100D's color gamut. The center of the gamut is completely unsaturated, or  white, gray, and black. Color saturation increases toward the edges of the chart, and the colors are arranged around the center like a color wheel. Each point on the chart indicates a unique combination of hue and saturation. The small squares on the gamut chart show where the GretagMacbeth colors should be, and the large circles show how the K100D rendered them. The distance between the two indicates inaccuracy in general, but the arrangement shows saturation and hues errors distinctly – when the circle is farther away from the center than the square, the color is oversaturated. When the circle points away from the center, it indicates a hue error.

The Pentax K100D delivers a respectable mean color error of 7.28 but high saturation, at 105.9 percent. That's a good figure for compact snapshot cameras, a market segment that typically punches up color. Good scores for DSLRs targeted toward enthusiasts are within 3 percent of perfect. The K100D delivered its best results on our tests with exposure compensation set to -0.3 EV, so users may want to underexpose in real-world shooting. We shot at the K100D's lowest ISO setting, which is 200.

 

We shoot our still-life scene with every camera we test, and post the full-resolution images to allow users to compare them. The fact that our procedure introduces scores of images of plastic sushi into the global data stream is just gravy, as far as we're concerned.

Resolution measures the amount of detail a camera can detect under ideal circumstances. We shoot our tests with cameras mounted on a heavy tripod and engage the self timer to prevent camera shake. In addition, we shoot at a variety of apertures and focal lengths, and report the best results. Again, we use Imatest software to measure resolution, based on images of a standard ISO resolution target. We report resolution in “line-widths per picture height,” (lw/ph), a unit of measure that is directly comparable between all the types of cameras we test. Imatest also reports the amount of sharpening performed on an image.

The Pentax K100D recorded 1253 lw/ph (horizontal), with 11.1 percent undersharpening and 1391 lw/ph (vertical), with 8.27 percent undersharpening. The lw/ph scores are poor, even considering the K100D's 6-megapixel image size. Even if the images were processed with image editing software to the ideal level of sharpness, the K100D would score poorly. The good news is that the K100D undersharpens, which is much easier to handle than oversharpening. Oversharpening can create halos and other artifacts that are practically impossible to remove from images. Our best test image was shot at f/10, with the lens set at 55mm.

Noise is the grainy texture that a camera adds to the image through technical flaws and the limitations of photo-electronic sensors and digital image processing. Though cameras can't eliminate noise completely, less noise is better, and digital cameras produce less noise at lower ISOs. We use Imatest software to measure noise. The ideal result for the Auto ISO noise test is for the camera to deliver the same results in Auto ISO as it does at its lowest manual ISO setting.

The Pentax K100D did exactly that – Auto ISO looked just like ISO 200, in our test. Of course, in real-world shooting situations, that wouldn't always be the case – in low light, the K100D's Auto setting would boost ISO, and noise would rise with it. In bright light, though, it works just as it should and its 10.32 Auto ISO Noise score reflects that.

Noise – Manual ISO (5.61)
The chart below displays the K100D’s noise levels at its various manual ISO ratings. The horizontal axis shows the camera’s ISO settings, with the correlating noise plotted along the vertical axis. Again, these shots were captured in a controlled studio setting, using Tungsten illumination.

We test low light performance at 60, 30, 15 and 5 lux. 60 lux is comfortable for reading, brighter than the typical living room. 5 lux is very dim, equivalent to the light cast by a single candle from about 1 ½ feet. We could not set a custom white balance with the Pentax K100D at 5 lux, so we used the tungsten preset. Though we tested the K100D both with noise reduction on and off, the score reflects its performance with noise reduction on.

The Pentax K100D scored well in our low light tests, with saturated colors even at our lowest tested light level. The K100D has a noise reduction algorithm, which kicks in on at exposures of 1 second or longer. The noise reduction system is slow – it takes roughly as long as the exposure itself.

 

We also tested the K100D's noise levels at various exposure durations. In general, noise levels go up as the exposure is prolonged. In the chart below, the exposure time is plotted on the horizontal axis, while the corresponding noise is shown on the vertical axis.

Dynamic Range (8.52)
Dynamic range refers to the span between the brightest and darkest values a camera can record with detail in a single image. We test dynamic range with Imatest software. We shoot images of a strip of film that shows a series of rectangles, running from nearly clear film to nearly opaque. The brightest rectangle is more than 14 EV brighter than the darkest, which is a wider range than any camera has recorded in our tests. Cameras' dynamic range performance deteriorates as ISOs increase, so we shoot at each full step in the ISO range. Imatest reports scores at a range of quality levels, which indicate how much noise is present at the extremes of the range. We report the “High Quality” result, which is limited to the range with 0.1 EV of noise or less.

The Pentax K100D recorded more than 7½ EV of dynamic range at ISO 200, and drops about ¾ of an EV at ISO 400 and 800. It dives by more than 1¼ EV from 800 to 1600, and drops another ¾ at 3200. These results are good for an entry-level DSLR, though they certainly indicate one of the advantages of shooting at low ISOs.

 

The Pentax K100D took 1 second from the moment we turned it on before its first shot. That's pretty quick for a consumer camera and quick enough for most users.

 

The Pentax K100D's Continuous Shooting mode is slow for a DSLR. The K100D took five shots in a row at 0.4-second intervals.  After 0.8 seconds, it took another shot, and then shot an image every 1.2 seconds. The K100D keeps up that pace until the card is filled.

 

The K100D has the speed advantage that all DSLRs have over compact cameras: there is very little lag between the moment the shutter is pressed and the moment the exposure is made. With the lens pre-focused, the K100D delays less than 0.1 seconds. Even if the camera has to focus, it can shoot with a delay as short as 0.1 second.

The K100D took 5 seconds to clear its buffer after shooting a 5-frame burst, so it takes about 1 second to record each image to media. This is slow for a DSLR and a limiting factor for its burst mode. Shooting action, the K100D user might well be frustrated while waiting for the camera to get back up to speed.

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