The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Pentax 18-250mm F3.5-6.3 and the Sigma 18-200mm F3.5-6.3 DC OS HSM C for their suitability to various photography scenarios:
Size and Weight Comparison
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. Sigma 18-200mm F3.5-6.3 DC OS HSM C weighs 430g, 5% (25g) lighter than the Pentax 18-250mm F3.5-6.3's weight of 455g.
Filter Threads
Both the Pentax 18-250mm F3.5-6.3 and the Sigma 18-200mm F3.5-6.3 DC OS HSM C have the same Filter thread size of 62mm.
Below are links to the 62mm filters that we recommend you to consider for these lenses:
Lens Mounts
The Pentax 18-250mm F3.5-6.3 has the Pentax KAF lens mount whereas the Sigma 18-200mm F3.5-6.3 DC OS HSM C 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.
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
Pentax 18-250mm F3.5-6.3 has a focal range of 18-250mm and
13.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27-375mm when used on a APS-C / DX format camera.
On the other hand, the 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.