The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Samyang 21mm F1.4 ED AS UMC CS 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. Samyang 21mm F1.4 ED AS UMC CS is the longer of the two lenses at 68mm. The Olympus M 25mm F1.8 with a length of 41mm, is 27mm shorter. Besides being longer, the Samyang 21mm F1.4 ED AS UMC CS also has a larger diameter of 64mm 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, 50% (139g) lighter than the Samyang 21mm F1.4 ED AS UMC CS's weight of 275g.
Filter Threads
The Samyang 21mm F1.4 ED AS UMC CS has a filter size of 58mm 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 58mm filters that we recommend you to consider for the Samyang 21mm F1.4 ED AS UMC CS:
And these are the 46mm filters that we recommend for the Olympus M 25mm F1.8:
Lens Mounts
Both the Samyang 21mm F1.4 ED AS UMC CS 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-1 II, Panasonic G9 II and OM System OM-5.
Samyang 21mm F1.4 ED AS UMC CS is also available in Canon EF-M , Fujifilm X and Sony E mounts.
Focal Range
Samyang 21mm F1.4 ED AS UMC CS is a prime lens with fixed focal lenght of 21mm which has an effective (full-frame 35mm equivalent) focal range of
42mm when used on a APS-C / DX 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.