The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Pentax 50-200mm F4-5.6 ED and the Pentax 18-135mm F3.5-5.6ED 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. Pentax 50-200mm F4-5.6 ED is the longer of the two lenses at 80mm. The Pentax 18-135mm F3.5-5.6ED with a length of 76mm, is 4mm shorter. On the other hand, the Pentax 18-135mm F3.5-5.6ED has a larger diameter of 73mm 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, which means it is 133g (32%) lighter than the Pentax 18-135mm F3.5-5.6ED which has a weight of 405g.
The Pentax 50-200mm F4-5.6 ED has the Pentax KAF lens mount whereas the Pentax 18-135mm F3.5-5.6ED has the Pentax KAF3 lens mount. Some of the latest released cameras that are compatible with these mounts are Pentax KF, Pentax K-3 III and Pentax KP for the Pentax KAF Mount and , and for the Pentax KAF3 Mount.
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. Pentax 18-135mm F3.5-5.6ED has a focal range of 18-135mm and 7.5X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-202.5mm when used on a APS-C / DX format camera.