The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Pentax FA 77mm 1.8 L and the Pentax DA 50-135mm F2.8 ED 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 DA 50-135mm F2.8 ED is the longer of the two lenses at 136mm. The Pentax FA 77mm 1.8 L with a length of 48mm, is 88mm shorter. Besides being longer, the Pentax DA 50-135mm F2.8 ED also has a larger diameter of 77mm compared to the Pentax FA 77mm 1.8 L's 64mm 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 FA 77mm 1.8 L weighs 270g, which means it is 415g (60%) lighter than the Pentax DA 50-135mm F2.8 ED which has a weight of 685g.
Filter Threads
The Pentax FA 77mm 1.8 L has a filter size of 49mm whereas the Pentax DA 50-135mm F2.8 ED has a 67mm 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 Pentax FA 77mm 1.8 L:
And these are the 67mm filters that we recommend for the Pentax DA 50-135mm F2.8 ED:
Lens Mounts
The Pentax FA 77mm 1.8 L has the Pentax KAF lens mount whereas the Pentax DA 50-135mm F2.8 ED has the Pentax KAF2 lens mount. Some of the latest released cameras that are compatible with these mounts are Pentax K-3 III Mono, Pentax KF and Pentax K-3 III for the Pentax KAF Mount and , and for the Pentax KAF2 Mount.
Focal Range
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.
On the other hand, the Pentax DA 50-135mm F2.8 ED has a focal range of 50-135mm and 2.7X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 75-202.5mm when used on a APS-C / DX format camera.
