The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Pentax 17-70mm F4.0 AL SDM 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. Pentax 17-70mm F4.0 AL SDM is the longer of the two lenses at 94mm. The Pentax DA 20-40mm F2.8-4 ED DC WR with a length of 69mm, is 25mm shorter. Besides being longer, the Pentax 17-70mm F4.0 AL SDM also has a larger diameter of 75mm compared to the Pentax DA 20-40mm F2.8-4 ED DC WR's 71mm 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, 41% (202g) lighter than the Pentax 17-70mm F4.0 AL SDM's weight of 485g.
Below you can find the dimension and weight table of the Standard Zoom Lenses in Pentax KAF3 Mount for size comparison purposes.
Standard Lenses in Pentax KAF3 Mount for Size Comparison
Filter Threads
The Pentax 17-70mm F4.0 AL SDM has a filter size of 67mm 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 67mm filters that we recommend you to consider for the Pentax 17-70mm F4.0 AL SDM:
And these are the 55mm filters that we recommend for the Pentax DA 20-40mm F2.8-4 ED DC WR:
Lens Mounts
Both the Pentax 17-70mm F4.0 AL SDM and the Pentax DA 20-40mm F2.8-4 ED DC WR has the same Pentax KAF3 lens mount. Some of the latest released cameras that are compatible with the Pentax KAF3 lenses are , and .
Focal Range
Pentax 17-70mm F4.0 AL SDM has a focal range of 17-70mm and
4.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
25.5-105mm when used on a APS-C / DX 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.
