The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 28-70mm F2.8 DG DN and the Pentax D FA 645 55mm F2.8 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. Sigma 28-70mm F2.8 DG DN is the longer of the two lenses at 102mm. The Pentax D FA 645 55mm F2.8 with a length of 68mm, is 34mm shorter. On the other hand, the Pentax D FA 645 55mm F2.8 has a larger diameter of 81mm compared to the Sigma 28-70mm F2.8 DG DN's 72mm 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 D FA 645 55mm F2.8 weighs 416g, 11% (54g) lighter than the Sigma 28-70mm F2.8 DG DN's weight of 470g.
Filter Threads
Both the Sigma 28-70mm F2.8 DG DN and the Pentax D FA 645 55mm F2.8 have the same Filter thread size of 67mm.
Below are links to the 67mm filters that we recommend you to consider for these lenses:
Lens Mounts
The Sigma 28-70mm F2.8 DG DN has the Sony E lens mount whereas the Pentax D FA 645 55mm F2.8 has the Pentax 645AF2 lens mount. Some of the latest released cameras that are compatible with these mounts are Sony FX5, Sony A7R VI and Sony A7 V for the Sony E Mount and Pentax 645Z, Pentax 645D and for the Pentax 645AF2 Mount.
Focal Range
Sigma 28-70mm F2.8 DG DN has a focal range of 28-70mm and
2.5X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
42 - 105mm.
On the other hand, the Pentax D FA 645 55mm F2.8 is a prime lens with fixed focal lenght of 55mm.
