The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-200mm F3.5-6.3 DC OS HSM C and the Pentax 50-200mm F4-5.6 ED WR 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. Sigma 18-200mm F3.5-6.3 DC OS HSM C is the longer of the two lenses at 86mm. The Pentax 50-200mm F4-5.6 ED WR with a length of 80mm, is 6mm shorter. Besides being longer, the Sigma 18-200mm F3.5-6.3 DC OS HSM C also has a larger diameter of 71mm compared to the Pentax 50-200mm F4-5.6 ED WR'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 WR weighs 285g, 33% (145g) lighter than the Sigma 18-200mm F3.5-6.3 DC OS HSM C's weight of 430g.
Filter Threads
The Sigma 18-200mm F3.5-6.3 DC OS HSM C has a filter size of 62mm whereas the Pentax 50-200mm F4-5.6 ED WR has a 49mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 62mm filters that we recommend you to consider for the Sigma 18-200mm F3.5-6.3 DC OS HSM C:
And these are the 49mm filters that we recommend for the Pentax 50-200mm F4-5.6 ED WR:
Lens Mounts
The Sigma 18-200mm F3.5-6.3 DC OS HSM C has the Pentax KAF3 lens mount whereas the Pentax 50-200mm F4-5.6 ED WR has the Pentax KAF lens mount. Some of the latest released cameras that are compatible with these mounts are , and for the Pentax KAF3 Mount and Pentax K-3 III Monochrome, Pentax KF and Pentax K-3 III for the Pentax KAF Mount.
Sigma 18-200mm F3.5-6.3 DC OS HSM C is also available in Canon EF , Nikon F (DX), Sony Alpha and Sigma SA mounts.
Focal Range
Sigma 18-200mm F3.5-6.3 DC OS HSM C has a focal range of 18-200mm and
11.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27-300mm when used on a APS-C / DX format camera.
On the other hand, the Pentax 50-200mm F4-5.6 ED WR 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.