The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Pentax FA 50mm F1.4 and the Sigma 18-35mm F1.8 DC 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. Sigma 18-35mm F1.8 DC HSM is the longer of the two lenses at 121mm. The Pentax FA 50mm F1.4 with a length of 41mm, is 80mm shorter. Besides being longer, the Sigma 18-35mm F1.8 DC HSM also has a larger diameter of 78mm compared to the Pentax FA 50mm F1.4's 65mm 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 FA 50mm F1.4 weighs 223g, which means it is 587g (72%) lighter than the Sigma 18-35mm F1.8 DC HSM which has a weight of 810g.
Filter Threads
The Pentax FA 50mm F1.4 has a filter size of 49mm whereas the Sigma 18-35mm F1.8 DC HSM has a 72mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 49mm filters that we recommend you to consider for the Pentax FA 50mm F1.4:
And these are the 72mm filters that we recommend for the Sigma 18-35mm F1.8 DC HSM:
Lens Mounts
Both the Pentax FA 50mm F1.4 and the Sigma 18-35mm F1.8 DC HSM 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 Mono, Pentax KF and Pentax K-3 III.
Pentax FA 50mm F1.4 is also available in the Pentax KAF mount.
Sigma 18-35mm F1.8 DC HSM is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Pentax FA 50mm F1.4 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 18-35mm F1.8 DC HSM has a focal range of 18-35mm and 1.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-52.5mm when used on a APS-C / DX format camera.
