The Sigma 20mm f/1.4 DG HSM ART is a super-glandular lens, among the brightest on the market, so much so that even setting the F/1.4 opening to which it is equipped, the resolution is excellent; as well as the correction of aberrations. Designed for the full frame, it also returns excellent results on the APS-C format. The integrated autofocus function makes use of an HSM engine; In addition, the Sigma provided the focusing option in a semi -automatic way, which makes the focus process even faster. Realized through the use of various special components, the zoom is characterized by 15 elements in 11 groups, including 2 F Low Despersion (which are the most precious of the Japanese house) and 5 special Low Despersion, which guarantee a low dispersion. The lenses are treated with anti -reflex to counter the risk of flare and ghosting. The blur is also extremely pleasant by means of the diaphragm with 9 circular slats adaptable with the Sigma dock in order to be able to program the mechanism and possibly solve the front/back-Focus problems. From the point of view of the structure we are surely faced with one of the maximum weights in terms of lenses: the scale marks 950 g. And the cost is certainly not cheap. However, the product is built very well, the design is finished and there is a large and comfortable ring for the MAF and a window that contains focal distances. The Sigma 20mm f/1.4 DG HSM Art is available for Nikon and Canon cameras and is ideal for photographers looking for a high -end professional lens, capable of giving a high level of sharpness to the images, an excellent chromatic yield, An autofocus function at the top of precision and able to guarantee excellent results both in external and internal environments.