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 and the Pentax 18-250mm F3.5-6.3 for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Pentax 18-250mm F3.5-6.3 is the longer of the two lenses at 86mm. The Sigma 18-200mm F3.5-6.3 DC with a length of 78mm is 8mm shorter. Besides being longer, the Pentax 18-250mm F3.5-6.3 also has a larger diameter of 75mm compared to Sigma 18-200mm F3.5-6.3 DC's 70mm diameter.
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. Sigma 18-200mm F3.5-6.3 DC weighs 405g, which means it is 50g (10%) lighter than the Pentax 18-250mm F3.5-6.3 which has a weight of 455g.
Below you can find the dimension and weight table of the 'SuperZoom Lenses in Pentax KAF Mount for size comparison purposes.
SuperZoom Lenses in Pentax KAF Mount for Size Comparison
Both Sigma 18-200mm F3.5-6.3 DC and Pentax 18-250mm F3.5-6.3 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 KP.
Sigma 18-200mm F3.5-6.3 DC is also available in Canon EF , Nikon F (DX), Sony Alpha and Sigma SA mounts.
Sigma 18-200mm F3.5-6.3 DC 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. 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.