The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Pentax 40mm F2.8 L and the Pentax FA 43mm F1.9 L 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 FA 43mm F1.9 L is the longer of the two lenses at 27mm. The Pentax 40mm F2.8 L with a length of 15mm, is 12mm shorter. Besides being longer, the Pentax FA 43mm F1.9 L also has a larger diameter of 64mm compared to the Pentax 40mm F2.8 L's 63mm 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 40mm F2.8 L weighs 80g, which means it is 75g (48%) lighter than the Pentax FA 43mm F1.9 L which has a weight of 155g.
Below you can find the dimension and weight table of the Standard Prime Lenses in Pentax KAF Mount for size comparison purposes.
Standard Lenses in Pentax KAF Mount for Size Comparison
Filter Threads
Both the Pentax 40mm F2.8 L and the Pentax FA 43mm F1.9 L have the same Filter thread size of 49mm.
Below are links to the 49mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the Pentax 40mm F2.8 L and the Pentax FA 43mm F1.9 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 40mm F2.8 L is also available in Pentax KAF mount.
Focal Range
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.
On the other hand, the Pentax FA 43mm F1.9 L is a prime lens with fixed focal lenght of 43mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 64.5mm.