What’s in a millimeter?
The main lenses we are looking at here are the Canon and Nikon versions of the Carl Zeiss Distagon T* 2.8/15 lens which was launched in March 2012. To give some perspective we are including the Sigma 14mm f2.8 EX Aspherical HSM Nikon that was launched around the middle of 2008 but is no-longer in production.
The Zeiss optic comprises 15 elements in 12 groups. Optically the two versions of the Zeiss Distagon are the same, but the Canon version is slightly longer and heavier due to differences in the depth of the camera body and the dimensions of the lens mount.
The Sigma lens comprises 14 elements in 10 groups in what, for such a wide lens, is a relatively compact 82mm across and just over 90mm long. Unlike the Zeiss lens, it also has autofocus, this seems a little superfluous in such a wide lens but is nice to have anyway. The Carl Zeiss lens, in either version, Canon or Nikon, is rather bigger: 103mm across and over 130mm long and also rather heavier. Both manufacturers are using aspheric elements and Zeiss also use special glass that they describe as ‘anomalous partial dispersion’, they also both have built in lens shades.
“Unsurprising” Test Results
In DxO Mark’s testing the quality of the Zeiss lenses over the Sigma lens is very clear. A DxO Mark score of 17 for the Sigma lens is an OK score for a lens with this extreme wide angle: there are few wider corrected lenses on the market to cover full frame 35mm so if the lens were considered in isolation the score might possibly be accepted as a reasonable consequence of the focal length. However, when you look at the other lenses in this category the score does not look quite as good. Zeiss on the other hand have a shining DxO Mark score of 23 for their Nikon version, the highest for any lens of 20mm or wider with a Nikon FX mount (the Canon version scores a creditable 21). The Zeiss lens is much more expensive, nearly 4 times the price of the Sigma, so there will obviously be people for whom the Zeiss is just too much.
The breakdown of the scores does give some relief for the Sigma lens, the three measures that can be corrected: Distortion, Vignetting and Chromatic Aberration all contribute quite heavily to the poor overall score and the proper application of digital corrections using DxO Optics Pro will certainly improve the overall situation immensely. However the sharpness score of just 9 P-Mpix (bearing in mind that the tests were carried out on a Nikon D3X which has a sensor of 24Mpix), means that post production is not going to redeem the lens entirely. Zeiss’s 15mm does much better, with a score of 16 P-Mpix for the Nikon version and 13 P-Mpix for the Canon. The Zeiss Distagon T* 2.8/15 in both it’s versions handles distortion and Chromatic aberration well. Vignetting is just what you would expect for both, super-wide lenses: the corners of the frame are darker by 1.9EV on the Zeiss and 2.6EV on the Sigma.
Alternative Super Wide Angle lenses: Sigma and Zeiss compared to Samyang 14mm f2.8 IF ED UMC Aspherical Nikon
Both Nikon and Canon have 14mm f2.8 lenses in their ranges, at the time of writing neither has been fully tested by DxO Mark, but reviews on both will follow soon. The lenses we have reviewed here are made by independent manufactures and there are others too. Samyang produce a 14mm f2.8 IF ED lens for Nikon and in other mounts too: Canon, Sony A and Pentax, it is well worth looking at, especially in comparison to the Sigma lens.
These three measures show the correctable errors in the lenses and on the basis of these results, you can see that the Zeiss lens is best overall. Of the other two the Samyang is better for chromatic aberration and the Sigma for distortion. The distortion on both the Sigma and especially on the Samyang lenses is irregular, showing corrections that swing from barrel to pin-cushion across the field, for architectural photographs there would be times when an un-corrected image would be completely unacceptable, whereas the Zeiss lens has a more consistent curve, this can be seen in the chart. When you look at the next chart however, the results are quite a shock!
Now the Samyang lens is the best of the three, it scores 18 M-Pix for sharpness, 2 M-Pix higher than the Zeiss lens and double the score of the Sigma. Sharpness is either there or it isn’t so this is an impressive coup for the Samyang, made even more impressive by the fact that it has a price tag less than one sixth of the Zeiss lens and almost half the cost of the Sigma. Taken as a whole the Zeiss Distagon T* 2.8/15 ZF.2 is the best of this group, the images captured with it are going to be better, straight from the camera than those captured by either of the other two. Once you look at value in the equation too, the results seem to favour the cheapest of the bunch, the Samyang 14mm f2.8 IF ED UMC Aspherical, with the addition of some post production from DxO Optics Pro it is likely that the final results would be better than could be achieved from any other independent lens of this focal length.
This is not an exhaustive test, it reviews data only for independent lenses and the camera manufactures own offerings obviously need to be considered too. However, on the strength of the data available it seems that the best lens is Carl Zeiss’s Distagon T* 2.8/15. For a photographer who plans to use a super wide-angle extensively in their work this is the one to go for. Images straight from camera are going to be superior to those from other lenses. The majority of photographers will not be using a 14 or 15mm lens so much and so would probably be better off saving some money and buying a Samyang 14mm f2.8 IF ED UMC Aspherical. With the money they save they should also buy a copy of DxO Optics Pro 8 and a return ticket to somewhere to play with their new toy!