The type of photography that you are planning to use is an important decision factor. Here we have evaluated the OM System 12-40mm F2.8 PRO II and the Pentax DA 20-40mm F2.8-4 ED DC WR 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. OM System 12-40mm F2.8 PRO II is the longer of the two lenses at 84mm. The Pentax DA 20-40mm F2.8-4 ED DC WR with a length of 69mm, is 15mm shorter. On the other hand, the Pentax DA 20-40mm F2.8-4 ED DC WR has a larger diameter of 71mm compared to the OM System 12-40mm F2.8 PRO II's 70mm 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 DA 20-40mm F2.8-4 ED DC WR weighs 283g, 25% (99g) lighter than the OM System 12-40mm F2.8 PRO II's weight of 382g.
Filter Threads
The OM System 12-40mm F2.8 PRO II has a filter size of 62mm whereas the Pentax DA 20-40mm F2.8-4 ED DC WR has a 55mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 62mm filters that we recommend you to consider for the OM System 12-40mm F2.8 PRO II:
And these are the 55mm filters that we recommend for the Pentax DA 20-40mm F2.8-4 ED DC WR:
Lens Mounts
The OM System 12-40mm F2.8 PRO II has the Micro Four Thirds lens mount whereas the Pentax DA 20-40mm F2.8-4 ED DC WR has the Pentax KAF3 lens mount. Some of the latest released cameras that are compatible with these mounts are OM System OM-3 Astro, OM System OM-5 II and OM System OM-3 for the Micro Four Thirds Mount and , and for the Pentax KAF3 Mount.
Focal Range
OM System 12-40mm F2.8 PRO II has a focal range of 12-40mm and
3.3X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
24-80mm when used on a FourThirds format camera.
On the other hand, the Pentax DA 20-40mm F2.8-4 ED DC WR has a focal range of 20-40mm and 2.0X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 30-60mm when used on a APS-C / DX format camera.
