Noise, Resolution and Sensitivity
Perhaps the most notable feature of the K-5 is its ISO range, which is expandable through the custom menu from its auto setting of 100-12,800 to a staggering ISO 80-51,200. Of all DSLRs with APS-C-size sensors, the Pentax K-5’s ISO of 51,200 has the highest sensitivity.
This is combined with a pixel output of up to 4928×3264 crammed into the APS-C-size sensor, which is an increase from the 4672×3104 pixels found in the K-7.
I am impressed with the level of detail in my images. Raw files are particularly sharp and images shot on our resolution charts reached 30 at ISO 100. Images shot at the maximum auto setting of ISO 12,800 still reached 24, which is equivalent to ISO 100 in many entry-level DSLRs. JPEG files are softer, but still resolve a lot of detail.
At ISO 100 files reach 28 and 24 at ISO 6400. JPEG files are softer still if noise reduction is applied. I turned off the noise reduction because distracting noise only really shows at much higher sensitivities, and in such conditions noise often adds atmosphere.
Although noise is evident at ISO 12,800, there is plenty of detail at this setting
Luminance noise is noticeable at around ISO 800, but only becomes striking from ISO 3200. Although obviously noisy, ISO 51,200 works in exceptionally low light and offers flash-free and atmospheric shooting.
Chroma noise comes into play at higher sensitivities too, and is most apparent in shadow areas, This can be helped a little by using shadow correction. To help counter distracting colour noise, images shot at such high sensitivities look much better converted to black & white.
Resolution charts: These images show 72ppi (100% on a computer screen) sections of images of a resolution chart, captured using a Sigma 105mm f/2.8 lens. We show the section of the resolution chart where the camera starts to fail to reproduce the lines separately. The higher the number visible in these images, the better the camera’s detail resolution is at the specified sensitivity setting.
