The Sony RX1 has been introduced at the same time as a number of other 35mm prime lenses designed for DSLRs. While DSLRs are more flexible, direct comparison between the cameras is still valid. At $899, the new Canon EF 35mm f/2 IS USM seems a little high in price and yet, at $2,999 when paired with the new full-frame Canon EOS 6D, for example, is a similar price to the RX1. It can’t be compared in size but, optically, the image stabilised Canon lens performs very well indeed. It has lower distortion and chromatic aberration than the Sony Zeiss lens, and the Transmission matches the theoretical aperture values.
The Canon also has similar levels of vignetting, close enough to be indistinguishable in real-world use. However, with a Sharpness score of 17P-Mpix, it’s not quite as sharp. But, this accounts for only part of the difference in the overall DxOMark Score of 29 for the Canon Vs 33 for the Sony Zeiss.
Some of this can be explained by the difference in the noise of the two camera’s sensors – the results of the Canon lens were measured with a Canon EOS 5D Mk II. The DxOMark Score takes into account of both the SNR and Color Sensitivity of the sensors. The results of the sensor comparison of the Sony Cyber-shot DSC-RX1 Vs Canon EOS 5D Mark II reveal the Sony camera has a 1/3rd stop advantage over the Canon model. Not only that, but the Color Sensitivity of the 24-Mpix Sony sensor has 1.5 bits difference or 2/3rd stop improvement at base ISO. These two points, a direct consequence of the sensor quality contribute to the higher DxOMark score of the Sony Zeiss over the Canon combination.
The same applies to the new Sigma. It’s a ‘faster’ lens but like the Canon it’s large physical size may count against it for discrete photography. However, few can argue that the optical quality isn’t remarkable. Although it loses out to the Sony in some areas it compares favourably. Indeed it has lower levels of CA and distortion, while vignetting is just 0.3 EV lower, quite extraordinary given the extra stop advantage at maximum aperture. The Sigma also has consistent sharpness across the frame, at least from f/2.8 onwards. Where it can’t quite match the Sony is the sharpness and homogeneity at f/2.0. Although sharper in the centre there’s more softness than the Sony at the edges.
All three autofocus lenses have very good sharpness and their performance is close. Nevertheless, the extra 1P-MPix score of the Sony Zeiss over the two main rivals can be explained simply enough. First, the Sony sensor has a slight advantage in pixel count over the Canon EOS 5D Mk II (albeit at the expense of efficiency) but mainly because the Zeiss is marginally sharper centrally across the f/2.8-f11 range of apertures than either the Sigma or the Canon. At f/2.0 the Sigma is sharper centrally than both the Zeiss and Canon, but it’s not enough to alter the overall score.