Noise, Resolution and Sensitivity
At lower sensitivities, the Alpha 77 is capable of crisp detail. This image was taken using the 16-50mm kit lens at f/4
Given the fixed mirror and high number of pixels, I was particularly interested with the Alpha 77’s resolution detail and ability to handle noise levels. In the controlled studio setting, the results from our resolution charts are pretty much in line with my expectations. Using our standard Sigma 105mm f/2.8 macro lens and shooting at ISO 100, resolution detail reaches the 32 marker on our charts in JPEG and raw format. This is highly impressive for a sensor of this size.
Of course, resolution detail is compromised as noise levels increase. With less light reaching the imaging sensor through the pellicle mirror (the Sony Alpha 580 DSLR uses the same sensor as the Alpha 55 SLT but handles noise better in low light), noise levels are slightly higher than the competition, such as those in the Nikon D7000 (according to www.dxomark.com). That said, noise is controlled rather well up to ISO 1600, with little effect on levels of detail – down to the 28 marker – despite luminance ‘grain’ starting to creep in from ISO 800.
Sony has stated that the unusual 71⁄3EV ISO range of 100-16,000 is because it was not satisfied with image quality at higher sensitivities. This proves to be a wise move, because at ISO 3200 luminance noise really starts to become apparent, with chroma noise, too, in unedited raw files. However, resolution detail remains high at the 24 marker.
The Alpha 77 matches the less-crowded Alpha 55 sensor in regards to levels of noise. Sony has therefore achieved the same performance with 50% extra pixels – an impressive feat.
In real-world scenes, it is clear that the 24.3-million-pixel sensor resolves a staggering level of detail, especially when used with a prime lens. Fine detail such as hair, eyelashes and blades of grass are crisp when shooting at any setting below ISO 800. Large prints at around 17×11.5in without interpolation at 350ppi are possible from the 6000×4000-pixel files.
Handily, the ISO range can be extended down to ISO 50, which is very useful in bright sunshine when faster apertures may be desired for portraits. That said, the Alpha 77 is capable of shooting at 1/8000sec so only at f/1.8 or wider is the slower ISO required.
Resolution charts: These images show 72ppi (100% on a computer screen) sections of images of a resolution chart, captured using a Sigma 105mm 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.
