Andy Westlake tests Pentax's latest fully featured mid-range DSLR with in-body image stabilisation
Pentax K-70 review – Dynamic range, resolution and noise
With its 24-million-pixel APS-C sensor, the K-70 offers image quality that’s at least a match for its peers and can only really be surpassed by much more expensive full-frame models. With a good lens, it records lots of detail at high ISOs, and image quality stands up really well as the ISO is raised. I was quite happy shooting at ISO 3200, and could live with ISO 25,600 at a pinch, but would avoid the top two settings. Raw shooters will be pleased to find that it can record using Adobe’s open-standard DNG format, which means that unlike other new models, you probably won’t need to update your raw conversion software to handle its files.
The K-S2 delivers very acceptable results in our Applied Imaging tests, broadly in line with its bigger brother the K-3 II, which also uses a 24-million-pixel APS-C sensor. Starting at 12.3EV at ISO 100, the readings initially decline only slowly to ISO 1600, where we still record almost 11EV. Beyond this, fall-off is more marked, indicating rapidly increasing noise levels, particularly in the shadows. By ISO 25,600, dynamic range has declined to a barely acceptable 6.3EV, with the higher ISO settings recording even lower readings, confirming their very marginal quality.
When shooting in raw, the K-70 can resolve at least 3600 lines/picture height. But the lack of a low-pass filter means that this comes with some moiré and false colour. This is suppressed by the camera’s JPEG processing, resulting in a clear drop in resolution to around 3200l/ph. Increasing the ISO further reduces resolution, to around 3000l/ph at ISO 6400 and 2600l/ph at ISO 25,600. The AA Filter Simulator reduces resolution to 3400l/ph at the Type 1 setting and 3000l/ph at Type 2, while reducing imaging artefacts.
Both raw and JPEG images taken from our diorama scene are captured at the full range of ISO settings. The camera is placed in its default setting for JPEG images. Raw images are sharpened and noise reduction applied, to strike the best balance between resolution and noise.
Looking at our standard test scene, the K-70 delivers detailed, noise-free results at ISO 100, which are a match for any current APS-C camera. As the sensitivity is raised, noise gradually increases, with the finest detail starting to suffer at around ISO 800. Even so, settings up to ISO 3200 are still eminently usable, and it’s only at ISO 6400 that low-frequency colour noise can start to creep into the camera’s JPEG files. At higher settings this gets more visible, as does luminance noise in the midtones, and personally I’d steer clear of ISO 51,200 and 102,400 unless it’s absolutely necessary, as the image quality at these settings is very marginal indeed. Switch to shooting raw and you get more control over noise reduction, which means that those top two sensitivity settings become slightly more usable, if still very much for emergencies only.