The Tamron SP 45mm f1.8 Di VC USD is in the same class of new standard lens based on inverted telephoto optical design. They are typically longer and heavier than traditional double Gauss lens design, with major improvement on edge sharpness at wide open aperture. Although not as fast as its f1.4 competitors from Zeiss and Sigma, the Tamron includes optical stabilization and weather seal at a lower cost.

PRO:
Image Quality: Very high resolution, both center and edge even wide open
Vibration control (VC): While most standard prime lens lack this feature, having VC makes this the lens of choice for night scene, indoor non-action shots, such as museum, art works and slow part of wedding ceremony. I can consistently hand-hold it at 1/8 sec.
Close focus: With minimum focus distance of 11.4” and a magnification of 0.29x, it is not a real macro lens. But it can get significantly closer than other standard lens. When combined with VC, and wide open aperture, it is perfect to capture small artifacts in museums and food in dim restaurants.
Robust Construction: Weather sealed. Although made with plastic, it feels rugged. The deep front and rear lens caps are much better than Canon’s.

CON:
Slow AF: On a 5DMk3, focus is not instant, but a fraction of a second slower than Canon L lens. On LiveView and on the original EOS M without dual-pixel AF, it moves very slowly but no hunt.
CA: More CA than even zoom lens, but easily correctable in post processing.
Physical Size: Longer and heavier than traditional 50mm lens. Same weight as Canon’s f1.2L. But only 2/3 the weight of contemporary inverted telephoto f1.4 lens from Sigma and Zeiss.