The Sigma 50-100mm f/1.8 DC HSM Art is a lens with optical construction that uses 21 elements including one SLD and 3 FLD elements. The Sigma Super Multi Multi Layer coating is designed to avoid the Ghost and Flare effect and all this in a 171 mm long device. A rather large size and with a weight of about 1500 grams, not exactly light. The Autofocus function is powered by the HSM engine which proves to be excellent for the speed of performance and the silence of the movement. The Sigma 50-100 mm f/1.8 A offers the photographer also the full time manual focus. The long body of the lens offers a large space used for focus and zoom rings, while the internal system ensures that the lens maintains the desired length even during operation. The rotating collar offers comfortable use both with tripod and with single-sided and sigma 50-100 mm f/1.8 A is compatible with the USB Sigma dock for updating the lens firmware and fine adjustment settings such as the position of the mass a fire. The sharpness of the image is excellent and uniform with an excess of 70% in the recovery field at 50 mm or 70 mm with slightly softer edges in the second focal length. At 100 mm, the resolution of f/1.8 drops to 65% of mite but the uniform sharpness in the corners remains very good. The Sigma lens reaches maximum sharpness with the use of diaphragms between f/2.8 AF/5.6 at all focal lengths with a slightly lower resolution using the closest opening settings between f/8 and f/16. The lens is able to manage chromatic aberrations optimally and with few proofs of fringes in any context. Ideal for : Sigma 50-100mm f/1.8 DC HSM ART is the ideal lens for professionals or photographers with advanced level capacity that do not require rapid movements but predict shots on fixed tripod.