The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Pentax 14mm F2.8 ED and the Sigma 15mm F2.8 EX DG Fisheye 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 14mm F2.8 ED is the longer of the two lenses at 69mm. The Sigma 15mm F2.8 EX DG Fisheye with a length of 65mm, is 4mm shorter. Besides being longer, the Pentax 14mm F2.8 ED also has a larger diameter of 84mm compared to the Sigma 15mm F2.8 EX DG Fisheye'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 15mm F2.8 EX DG Fisheye weighs 370g, 11% (50g) lighter than the Pentax 14mm F2.8 ED's weight of 420g.
Lens Mounts
Both the Pentax 14mm F2.8 ED and the Sigma 15mm F2.8 EX DG Fisheye 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.
Sigma 15mm F2.8 EX DG Fisheye is also available in Canon EF , Nikon F (FX), Sony Alpha and Sigma SA mounts.
Focal Range
Pentax 14mm F2.8 ED is a prime lens with fixed focal lenght of 14mm which has an effective (full-frame 35mm equivalent) focal range of
21mm when used on a APS-C / DX format camera.
On the other hand, the Sigma 15mm F2.8 EX DG Fisheye is a prime lens with fixed focal lenght of 15mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 22.5mm.