The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron 70-200mm f2.8 LD and the Pentax 50-200mm F4-5.6 ED for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is an important deciding factor when comparing two lenses. Tamron 70-200mm f2.8 LD is the longer of the two lenses at 194mm. The Pentax 50-200mm F4-5.6 ED with a length of 80mm, is 114mm shorter. Besides being longer, the Tamron 70-200mm f2.8 LD also has a larger diameter of 90mm compared to the Pentax 50-200mm F4-5.6 ED's 69mm diameter.
The 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. Pentax 50-200mm F4-5.6 ED weighs 272g, 79% (1058g) lighter than the Tamron 70-200mm f2.8 LD's weight of 1330g.
Below you can find the dimension and weight table of the Telephoto Zoom Lenses in Pentax KAF Mount for size comparison purposes.
Telephoto Zoom Lenses in Pentax KAF Mount for Size Comparison
Lens Mounts
Both the Tamron 70-200mm f2.8 LD and the Pentax 50-200mm F4-5.6 ED has the same Pentax KAF lens mount. Some of the latest released cameras that are compatible with the Pentax KAF lenses are Pentax KF, Pentax K-3 III and Pentax K-1 II.
Tamron 70-200mm f2.8 LD is also available in Canon EF , Nikon F (FX) and Sony Alpha mounts.
Focal Range
Tamron 70-200mm f2.8 LD has a focal range of 70-200mm and 2.9X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 105 - 300mm.
Pentax 50-200mm F4-5.6 ED has a focal range of 50-200mm and 4.0X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 75-300mm when used on a APS-C / DX format camera.