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 a crucial factor to consider 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 equally significant as its external dimensions, particularly if you intend to handhold your camera and lens combination for extended 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.
Filter Threads
The Pentax 50-200mm F4-5.6 ED has a filter size of 49mm whereas the Pentax 18-135mm F3.5-5.6ED has a 62mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 49mm filters that we recommend you to consider for the Pentax 50-200mm F4-5.6 ED:
And these are the 62mm filters that we recommend for the Pentax 18-135mm F3.5-5.6ED:
Lens Mounts
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 K-3 III Monochrome, Pentax KF and Pentax K-3 III for the Pentax KAF Mount and , and for the Pentax KAF3 Mount.
Focal Range
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.
On the other hand, the 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.