Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Canon 24-70mm f2.8L USM is the longer of the two lenses at 124mm. The Tamron AF 28-80mm f3.5-5.6 with a length of 70mm is 54mm shorter. Besides being longer, the Canon 24-70mm f2.8L USM also has a larger diameter of 83mm compared to Tamron AF 28-80mm f3.5-5.6's 72mm diameter.
Weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Tamron AF 28-80mm f3.5-5.6 weighs 237g, which means it is 713g (75%) lighter than the Canon 24-70mm f2.8L USM which has a weight of 950g.
Below you can find the dimension and weight table of the 'Standard Zoom Lenses in Canon EF Mount for size comparison purposes.
Standard Zoom Lenses in Canon EF Mount for Size Comparison
Both Tamron AF 28-80mm f3.5-5.6 and Canon 24-70mm f2.8L USM has the same Canon EF lens mount. Some of the latest released cameras that are compatible with the Canon EF lenses are Canon 1D X III, Canon 6D MII and Canon 5D MIV.
Tamron AF 28-80mm f3.5-5.6 is also available in Nikon F (FX) , Sony Alpha and Pentax KAF mounts.
Tamron AF 28-80mm f3.5-5.6 has a focal range of 28-80mm and 2.9X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides an 35mm (FF) equivalent of 44.8 - 128mm.
Canon 24-70mm f2.8L USM has a focal range of 24-70mm and 2.9X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides an 35mm (FF) equivalent of 38.4 - 112mm.