The type of photography that you are planning to use is an important decision factor. Here we have evaluated the HD Pentax-DA 10-17mm F3.5-4.5 ED fisheye and the Samyang 20mm F1.8 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. Samyang 20mm F1.8 is the longer of the two lenses at 88mm. The HD Pentax-DA 10-17mm F3.5-4.5 ED fisheye with a length of 70mm, is 18mm shorter. Besides being longer, the Samyang 20mm F1.8 also has a larger diameter of 83mm compared to the HD Pentax-DA 10-17mm F3.5-4.5 ED fisheye's 68mm 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. HD Pentax-DA 10-17mm F3.5-4.5 ED fisheye weighs 317g, which means it is 180g (36%) lighter than the Samyang 20mm F1.8 which has a weight of 497g.
Both the HD Pentax-DA 10-17mm F3.5-4.5 ED fisheye and the Samyang 20mm F1.8 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.
Samyang 20mm F1.8 is also available in Canon EF , Canon EF-M, Fujifilm X, Micro Four Thirds, Nikon F (FX), Samsung NX, Sony Alpha and Sony E mounts.
HD Pentax-DA 10-17mm F3.5-4.5 ED fisheye has a focal range of 10-17mm and 1.7X
zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 15-25.5mm
when used on a APS-C / DX format camera.
On the other hand, the Samyang 20mm F1.8 is a prime lens with fixed focal lenght of 20mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 30mm.