The type of photography that you are planning to use is an important decision factor. Here we have evaluated the HD Pentax-FA 43mm F1.9 Ltd and the Pentax 50mm 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. Pentax 50mm F1.8 is the longer of the two lenses at 39mm. The HD Pentax-FA 43mm F1.9 Ltd with a length of 27mm, is 12mm shorter. On the other hand, the HD Pentax-FA 43mm F1.9 Ltd has a larger diameter of 64mm compared to the Pentax 50mm F1.8'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 50mm F1.8 weighs 122g, 21% (33g) lighter than the HD Pentax-FA 43mm F1.9 Ltd's 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
The HD Pentax-FA 43mm F1.9 Ltd has a filter size of 49mm whereas the Pentax 50mm F1.8 has a 52mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 49mm filters that we recommend you to consider for the HD Pentax-FA 43mm F1.9 Ltd:
And these are the 52mm filters that we recommend for the Pentax 50mm F1.8:
Lens Mounts
Both the HD Pentax-FA 43mm F1.9 Ltd and the Pentax 50mm 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.
Focal Range
HD Pentax-FA 43mm F1.9 Ltd 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.
On the other hand, the Pentax 50mm F1.8 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 a 35mm (FF) equivalent of 75mm.