The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Pentax 70mm F2.4 AL L and the Pentax FA 77mm 1.8 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 77mm 1.8 L is the longer of the two lenses at 48mm. The Pentax 70mm F2.4 AL L with a length of 26mm, is 22mm shorter. Besides being longer, the Pentax FA 77mm 1.8 L also has a larger diameter of 64mm compared to the Pentax 70mm F2.4 AL 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 70mm F2.4 AL L weighs 130g, which means it is 140g (51%) lighter than the Pentax FA 77mm 1.8 L which has a weight of 270g.
Filter Threads
Both the Pentax 70mm F2.4 AL L and the Pentax FA 77mm 1.8 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 70mm F2.4 AL L and the Pentax FA 77mm 1.8 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 70mm F2.4 AL L is also available in Pentax KAF mount.
Focal Range
Pentax 70mm F2.4 AL L is a prime lens with fixed focal lenght of 70mm which has an effective (full-frame 35mm equivalent) focal range of
105mm when used on a APS-C / DX format camera.
On the other hand, the Pentax FA 77mm 1.8 L is a prime lens with fixed focal lenght of 77mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 115.5mm.