The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon RF 28mm F2.8 STM and the Pentax 18-135mm F3.5-5.6ED 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 18-135mm F3.5-5.6ED is the longer of the two lenses at 76mm. The Canon RF 28mm F2.8 STM with a length of 25mm, is 51mm shorter. Besides being longer, the Pentax 18-135mm F3.5-5.6ED also has a larger diameter of 73mm compared to the Canon RF 28mm F2.8 STM's 69mm 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. Canon RF 28mm F2.8 STM weighs 120g, which means it is 285g (70%) lighter than the Pentax 18-135mm F3.5-5.6ED which has a weight of 405g.
Filter Threads
The Canon RF 28mm F2.8 STM has a filter size of 55mm whereas the Pentax 18-135mm F3.5-5.6ED has a 62mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 55mm filters that we recommend you to consider for the Canon RF 28mm F2.8 STM:
And these are the 62mm filters that we recommend for the Pentax 18-135mm F3.5-5.6ED:
Lens Mounts
The Canon RF 28mm F2.8 STM has the Canon RF lens mount whereas the Pentax 18-135mm F3.5-5.6ED has the Pentax KAF3 lens mount. Some of the latest released cameras that are compatible with these mounts are Canon R6 V, Canon R6 III and Canon C50 for the Canon RF Mount and , and for the Pentax KAF3 Mount.
Focal Range
Canon RF 28mm F2.8 STM is a prime lens with fixed focal lenght of 28mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of
44.8mm.
On the other hand, the Pentax 18-135mm F3.5-5.6ED has a focal range of 18-135mm and 7.5X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-202.5mm when used on a APS-C / DX format camera.
