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 K10D proved to have the same actual sensitivity as was indicated, hence ISO 100 really was ISO 100.

ISO Sensitivity / Noise levels

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.

Pentax K10D vs. Nikon D80 vs. Canon EOS 30D

• Pentax K10D: Pentax 50 mm F1.4 lens, Aperture Priority, Manual WB,
  Default Parameters (Natural), JPEG Large / Fine
   
• Nikon D80: Nikkor 50 mm F1.4 Macro lens, Aperture Priority, Manual WB,
  Default Parameters (Normal), High ISO NR (Normal), JPEG Large / Fine
   
• Canon EOS 30D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
  Default Parameters (Standard PS), JPEG Large / Fine
  

Pentax K10D ISO 100	Nikon D80 ISO 100	Canon EOS 30D ISO 100 (125 equiv.)
Pentax K10D ISO 200	Nikon D80 ISO 200	Canon EOS 30D ISO 200 (250 equiv.)
Pentax K10D ISO 400	Nikon D80 ISO 400	Canon EOS 30D ISO 400 (500 equiv.)
Pentax K10D ISO 800	Nikon D80 ISO 800	Canon EOS 30D ISO 800 (1000 equiv.)
Pentax K10D ISO 1600	Nikon D80 ISO 1600	Canon EOS 30D ISO 1600 (2000 equiv.)
Pentax K10D n/a	Nikon D80 ISO 3200	Canon EOS 30D ISO 3200 (4000 equiv.)

As seems to be the case with most recent digital SLR's there is almost no difference in noise levels between these three cameras from ISO 100 to 400. At ISO 800 the D80 looks cleaner, a glance at the graph below tells you why, it's when Nikon's noise reduction kicks in properly and that also has some effect on detail. At ISO 1600 the most noteworthy feature of the K10D crop is the strength and visibility of chroma noise in the gray patch although it should also be noted that detail levels are still good.

Overall I would say that Pentax are using a minimal amount of noise reduction in order to maintain as much detail as possible, and that at ISO 1600 the K10D comes third place for noise (most of that chroma) and second place behind the EOS 30D for detail.

Luminance noise graph

Here we've also chosen to include the ten megapixel Sony DSLR-A100. As you can see the Nikon D80 is the only camera to really give any obvious sign that its noise reduction begins at a certain point (ISO 800 in this case). The K10D has a fairly nice predictable ramp in noise, which for mid-tones (gray) is very close to that of the EOS 30D but is slightly higher for shadow noise.

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

Chroma (color) noise graph

As was obvious from the crops the K10D exhibits a certain amount of its noise as 'chroma' (color blotches), its chroma noise graph being not that dissimilar to the Sony DSLR-A100 beyond ISO 400. Note that using the 'Bright' image tone only leads to higher noise figures (because of stronger color saturation and sharpening).

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