Pentax K100D Review: 14. Photographic tests: Digital Photography Review

ISO / Sensitivity accuracy

In a new addition to our reviews we are now measuring the actual sensitivity of each indicated ISO sensitivity. This is achieved using the same shots as are used to measure ISO noise levels, we simply compare the exposure for each shot to the metered light level (using Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV.

The K100D's ISO sensitivity proved to be exactly as indicated, throughout the ISO range.

Indicated sensitivity	Canon EOS 350D (actual sensitivity)	Pentax K100D (actual sensitivity)	Nikon D50 (actual sensitivity)
ISO 100	ISO 125	n/a	n/a
ISO 200	ISO 250	ISO 200	ISO 200
ISO 400	ISO 500	ISO 400	ISO 400
ISO 800	ISO 1000	ISO 800	ISO 800
ISO 1600	ISO 2000	ISO 1600	ISO 1600
ISO 3200	n/a	ISO 3200	n/a

ISO Sensitivity / Noise levels

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. The works by turning up the "volume" (gain) on the sensor's signal amplifiers (remember the sensor is an analogue device). By amplifying the signal you also amplify the noise which becomes more visible at higher ISO's. Many modern cameras also employ noise reduction and / or sharpness reduction at higher sensitivities.

To measure noise levels we take a sequence of images of a GretagMacBeth ColorChecker chart (controlled artificial daylight lighting). The exposure is matched to the ISO (ie. ISO 200, 1/200 sec for consistency of exposure between cameras). The image sequence is run through our own proprietary noise measurement tool (version 1.4 in this review). Click here for more information. (Note that noise values indicated on the graphs here can not be compared to those in other reviews). Room temperature is approximately 22°C (~72°F), simulated daylight lighting.

We would liked to have included the recently announced D40 but it was not available at the time these tests were produced, however we will include results from the K100D in our D40 review.

Pentax K100D vs. Canon EOS 350D (Rebel XT) vs. Nikon D50

Pentax K100D: Pentax 50 mm F1.4 lens, Aperture Priority, Manual WB,
Default Parameters (Vivid Tone), JPEG Large / Best
Canon EOS 350D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
Default Parameters (Standard PS), JPEG Large / Fine
Nikon D50: Nikkor 50 mm F1.8 lens, Aperture Priority, Manual WB,
Default Parameters (Normal), JPEG Large / Fine

Pentax K100D n/a	Canon EOS 350D ISO 100 (125 equiv.)	Nikon D50 n/a


Pentax K100D ISO 200	Canon EOS 350D ISO 200 (250 equiv.)	Nikon D50 ISO 200


Pentax K100D ISO 400	Canon EOS 350D ISO 400 (500 equiv.)	Nikon D50 ISO 400


Pentax K100D ISO 800	Canon EOS 350D ISO 800 (1000 equiv.)	Nikon D50 ISO 800


Pentax K100D ISO 1600	Canon EOS 350D ISO 1600 (2000 equiv.)	Nikon D50 ISO 1600


Pentax K100D ISO 3200	Canon EOS 350D n/a	Nikon D50 n/a

Up to ISO 800 the K100D maintains a similar level of noise as the Canon EOS 350D (Rebel XT), without sacrificing detail, at ISO 1600 the EOS 350D image is looking cleaner but also softer with the K100D demonstrating sharp detail if a little too much noise. Nikon's approach appears to be more noise reduction, especially luminance in 'flat areas'. The graph below reflects this performance, with the K100D very close to the EOS 350D for gray luminance noise but higher for black luminance noise (shadow noise).

Luminance noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.

Chroma (color) noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of color on the vertical axis.

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