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 Olympus M 25mm F1.8 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. OM System 12-40mm F2.8 PRO II is the longer of the two lenses at 84mm. The Olympus M 25mm F1.8 with a length of 41mm, is 43mm shorter. Besides being longer, the OM System 12-40mm F2.8 PRO II also has a larger diameter of 70mm compared to the Olympus M 25mm F1.8's 56mm 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. Olympus M 25mm F1.8 weighs 136g, 64% (246g) 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 Olympus M 25mm F1.8 has a 46mm 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 46mm filters that we recommend for the Olympus M 25mm F1.8:
Lens Mounts
Both the OM System 12-40mm F2.8 PRO II and the Olympus M 25mm F1.8 has the same Micro Four Thirds lens mount. Some of the latest released cameras that are compatible with the Micro Four Thirds lenses are OM System OM-3 Astro, OM System OM-5 II and OM System OM-3.
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 Olympus M 25mm F1.8 is a prime lens with fixed focal lenght of 25mm which has an effective (full-frame 35mm equivalent) focal range of 50mm when used on a FourThirds format camera.
