The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Pentax 21mm F3.2 AL L and the Pentax 15mm F4 ED AL L for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is an important deciding factor when comparing two lenses. Pentax 15mm F4 ED AL L is the longer of the two lenses at 40mm. The Pentax 21mm F3.2 AL L with a length of 25mm, is 15mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 63mm.
The 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 21mm F3.2 AL L weighs 134g, which means it is 55g (29%) lighter than the Pentax 15mm F4 ED AL L which has a weight of 189g.
Below you can find the dimension and weight table of the Wideangle Prime Lenses in Pentax KAF Mount for size comparison purposes.
Wideangle Prime Lenses in Pentax KAF Mount for Size Comparison
Lens Mounts
Both the Pentax 21mm F3.2 AL L and the Pentax 15mm F4 ED AL L 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.
Pentax 21mm F3.2 AL L is also available in Pentax KAF mount.
Focal Range
Pentax 21mm F3.2 AL L is a prime lens with fixed focal lenght of 21mm which has an effective (full-frame 35mm equivalent) focal range of 31.5mm when used on a APS-C / DX format camera. Pentax 15mm F4 ED AL L is a prime lens with fixed focal lenght of 15mm which has an effective (full-frame 35mm equivalent) focal range of 22.5mm when used on a APS-C / DX format camera.