Conclusion

Rebooting an established optical design, the weather-proof Zeiss Milvus 21mm f/2.8 is an excellent ultra-wide-angle prime lens for photographers who have the time and patience to focus manually. You’d expect sharpness to be high across both the frame and aperture range from such a premium optic, and it doesn't disappoint. In conjunction with the Canon EOS 5DS R test camera shooting at 50 megapixel resolution, detail is exceptionally detailed and sharp. Shooting at the maximum f/2.8 aperture does reveal a minor reduction in sharpness across the frame compared to the rest of the aperture range, but the image is already pin-sharp by f/4.

The Zeiss Milvus 21mm f/2.8 is a pleasure to use, thanks to its superb build quality and smooth focus ring. As this is a manual-focus only lens, you'd expect this aspect of the operation to be intuitive, and so it proved, although the Canon EOS 5Ds isn't really geared up for accurate manual focusing - we much preferred using it on a Sony A7R II camera via a Metabones adapter, where peaking really helps speed up the process. The fact that it's also weather-sealed is a real plus point when comparing it to its main rivals.

The equally new Sigma 20mm f/1.4 Art is faster, cheaper and offers auto-focusing, but it's even bigger than the Zeiss Milvus 21mm f/2.8, isn't weather sealed, doesn't have quite the same high level of build quality, and you can't fit circular filters thanks to its large, bulbous front element. Both lenses are excellent optically though, making it tough to choose between them...

Ratings (out of 5)
Design	4.5
Features	4.5
Ease-of-use	4.5
Image quality	4.5
Value for money	4