Not quite a 50mm lens, the Tamron 45mm gives a slightly more generous viewing angle of 51 degrees, rather than the more usual 46 degrees, on a full-frame body. Suffice it to say, there’s very little in it. The bigger 45mm combines a fairly fast f/1.8 aperture rating with 4-stop stabilization. Physically, it’s slightly smaller than the Sigma and Zeiss 50mm lenses and rather more lightweight.At 540g, it’s about two-thirds the weight of the Sigma and a little more than half the weight of the Zeiss 50mm. That being said, it’s still almost twice as heavy as the Canon EF 50mm f/1.4.
Build quality is considerably better than in either of the Canon EF lenses and not far off that of the Sigma. A bonus that you can find over all three is that the Tamron features extensive weatherseals and a fluorine coating on its front element, to repel water and greasy fingerprints, and to aid easy cleaning. Its ring-type ultrasonic autofocus system is fast and accurate, beating that of the Canon 50mm f/1.4 lens on both counts. As usual with this type of system, manual override is available in One Shot AF mode.