The type of photography that you are planning to use is an important decision factor. Here we have evaluated the HD Pentax-D FA 50mm F1.4 SDM AW and the Sigma 18-50mm F2.8-4.5 DC OS HSM 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. HD Pentax-D FA 50mm F1.4 SDM AW is the longer of the two lenses at 106mm. The Sigma 18-50mm F2.8-4.5 DC OS HSM with a length of 89mm, is 17mm shorter. Besides being longer, the HD Pentax-D FA 50mm F1.4 SDM AW also has a larger diameter of 80mm compared to the Sigma 18-50mm F2.8-4.5 DC OS HSM's 74mm 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. Sigma 18-50mm F2.8-4.5 DC OS HSM weighs 395g, 56% (515g) lighter than the HD Pentax-D FA 50mm F1.4 SDM AW's weight of 910g.
Lens Mounts
Both the HD Pentax-D FA 50mm F1.4 SDM AW and the Sigma 18-50mm F2.8-4.5 DC OS HSM has the same Pentax KAF3 lens mount. Some of the latest released cameras that are compatible with the Pentax KAF3 lenses are Pentax K-3 III Mono, Pentax KF and Pentax K-3 III.
Sigma 18-50mm F2.8-4.5 DC OS HSM is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
HD Pentax-D FA 50mm F1.4 SDM AW is a prime lens with fixed focal lenght of 50mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
75mm.
On the other hand, the 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.
