Sony Cyber-shot RX1 / Carl Zeiss Sonnar T* 2/35 review: Is this the ultimate moderate wide-angle lens?

By Kevin Carter - Friday, February 22, 2013

Lens Review
Introduction | Sony RX1 lens performance | Sony RX1 lens versus competition | Conclusion

Sony Cyber shot DSC RX1 lens Vs Canon EF 35mm f/2 IS USM Vs Sigma 35mm F1.4 DG HSM A Canon both last on Canon EOS 5D Mark II

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 lower noise levels of the RX1 sensor over the Canon EOS 5D Mk II go some way to improve DxOMark score for the Zeiss
The Sony RX1 has a very high quality sensor with superior color response and that contributes to the high DxOMark score of the RX1

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.

The Sony Zeiss has more consistent sharpness across the frame at maximum aperture (f/2.0), but the Canon is sharper centrally. The Sigma (shown right) has lower acutance but this particular field map is at f/1.4
At f/2.0 the Sigma shows improvement in the outer field when stopped down, and is slightly sharper in the centre than the other two but the acutance is marginally lower at the edges and corners than the Zeiss.
When stopped down from f/2.8 onwards there isn’t much between the three though the Zeiss is the most consistent across the frame, while the Canon has slightly lower acutance in the outer field.

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.

At f/2.0 the Zeiss performs well but both the Canon and the Sigma are marginally sharper centrally.