Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Sony 300mm F2.8 G is the longer of the two lenses at 243mm. The Samyang 300mm f6.3 with a length of 74mm is 169mm shorter. Besides being longer, the Sony 300mm F2.8 G also has a larger diameter of 122mm compared to Samyang 300mm f6.3's 65mm 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. Samyang 300mm f6.3 weighs 260g, which means it is 2050g (788%) lighter than the Sony 300mm F2.8 G which has a weight of 2310g.
Both Samyang 300mm f6.3 and Sony 300mm F2.8 G has the same Sony Alpha lens mount. Some of the latest released cameras that are compatible with the Sony Alpha lenses are Sony A68, Sony A77 II and Sony A58.
Samyang 300mm f6.3 is also available in Canon EF , Nikon F (DX) and Four Thirds mounts.