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 Pentax 40mm F2.8 L for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.HD Pentax-D FA 50mm F1.4 SDM AW is the longer of the two lenses at 106mm. The Pentax 40mm F2.8 L with a length of 15mm is 91mm shorter. Besides being longer, the HD Pentax-D FA 50mm F1.4 SDM AW also has a larger diameter of 80mm compared to Pentax 40mm F2.8 L's 63mm diameter.
Weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Pentax 40mm F2.8 L weighs 90g, 90% (820g) lighter than the HD Pentax-D FA 50mm F1.4 SDM AW's weight of 910g.
Both HD Pentax-D FA 50mm F1.4 SDM AW has the Pentax KAF3 lens mount whereas the Pentax 40mm F2.8 L has the Pentax KAF lens mount. Some of the latest released cameras that are compatible with these mounts are Pentax KF, Pentax K-3 III and Pentax K-1 II for the Pentax KAF3 Mount and Pentax KF, Pentax K-3 III and Pentax KP for the Pentax KAF Mount.
Pentax 40mm F2.8 L is also available in Pentax KAF mount.
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 an 35mm (FF) equivalent of 75mm.
Pentax 40mm F2.8 L is a prime lens with fixed focal lenght of 40mm which has an effective (full-frame 35mm equivalent) focal range of 60mm when used on a APS-C / DX format camera.