The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron AF 28-300mm f3.5-6.3 XR LD and the Pentax 18-250mm F3.5-6.3 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 18-250mm F3.5-6.3 is the longer of the two lenses at 86mm. The Tamron AF 28-300mm f3.5-6.3 XR LD with a length of 84mm, is 2mm shorter. Besides being longer, the Pentax 18-250mm F3.5-6.3 also has a larger diameter of 75mm compared to the Tamron AF 28-300mm f3.5-6.3 XR LD's 73mm 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. Tamron AF 28-300mm f3.5-6.3 XR LD weighs 420g, which means it is 35g (7%) lighter than the Pentax 18-250mm F3.5-6.3 which has a weight of 455g.
Filter Threads
Both the Tamron AF 28-300mm f3.5-6.3 XR LD and the Pentax 18-250mm F3.5-6.3 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
Both the Tamron AF 28-300mm f3.5-6.3 XR LD and the 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 K-3 III Monochrome, Pentax KF and Pentax K-3 III.
Tamron AF 28-300mm f3.5-6.3 XR LD is also available in Canon EF , Nikon F (FX) and Sony Alpha mounts.
Focal Range
Tamron AF 28-300mm f3.5-6.3 XR LD has a focal range of 28-300mm and
10.7X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
42 - 450mm.
On the other hand, the 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.