The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-50mm F2.8-4.5 DC OS HSM and the Pentax 16-45mm F4 ED AL 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 16-45mm F4 ED AL is the longer of the two lenses at 92mm. The Sigma 18-50mm F2.8-4.5 DC OS HSM with a length of 89mm, is 3mm shorter. On the other hand, the Sigma 18-50mm F2.8-4.5 DC OS HSM has a larger diameter of 74mm compared to the Pentax 16-45mm F4 ED AL's 72mm 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 16-45mm F4 ED AL weighs 356g, 9% (39g) lighter than the Sigma 18-50mm F2.8-4.5 DC OS HSM's weight of 395g.
Filter Threads
Both the Sigma 18-50mm F2.8-4.5 DC OS HSM and the Pentax 16-45mm F4 ED AL have the same Filter thread size of 67mm.
Below are links to the 67mm filters that we recommend you to consider for these lenses:
Lens Mounts
The Sigma 18-50mm F2.8-4.5 DC OS HSM has the Nikon F (DX) lens mount whereas the Pentax 16-45mm F4 ED AL has the Pentax 645AF2 lens mount. Some of the latest released cameras that are compatible with these mounts are Nikon D3500, Nikon D7500 and Nikon D5600 for the Nikon F (DX) Mount and , and for the Pentax 645AF2 Mount.
Sigma 18-50mm F2.8-4.5 DC OS HSM is also available in the Canon EF , Pentax KAF3, Sony Alpha and Sigma SA mounts.
Focal Range
Sigma 18-50mm F2.8-4.5 DC OS HSM has a focal range of 18-50mm and
2.8X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27-75mm when used on a APS-C / DX format camera.
On the other hand, the Pentax 16-45mm F4 ED AL has a focal range of 16-45mm and 2.8X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 24-67.5mm when used on a APS-C / DX format camera.
