The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon EF 50mm f/1.8 STM and the Canon 40mm f2.8 STM 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. Canon EF 50mm f/1.8 STM is the longer of the two lenses at 39mm. The Canon 40mm f2.8 STM with a length of 22mm, is 17mm shorter. Besides being longer, the Canon EF 50mm f/1.8 STM also has a larger diameter of 69mm compared to the Canon 40mm f2.8 STM's 68mm 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 40mm f2.8 STM weighs 130g, 18% (29g) lighter than the Canon EF 50mm f/1.8 STM's weight of 159g.
Below you can find the dimension and weight table of the Standard Prime Lenses in Canon EF Mount for size comparison purposes.
Standard Lenses in Canon EF Mount for Size Comparison
Filter Threads
The Canon EF 50mm f/1.8 STM has a filter size of 49mm whereas the Canon 40mm f2.8 STM has a 52mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 49mm filters that we recommend you to consider for the Canon EF 50mm f/1.8 STM:
And these are the 52mm filters that we recommend for the Canon 40mm f2.8 STM:
Lens Mounts
Both the Canon EF 50mm f/1.8 STM and the Canon 40mm f2.8 STM has the same Canon EF lens mount. Some of the latest released cameras that are compatible with the Canon EF lenses are Canon 1D X III, Canon 6D MII and Canon 5D MIV.
Focal Range
Canon EF 50mm f/1.8 STM is a prime lens with fixed focal lenght of 50mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of
80mm.
On the other hand, the Canon 40mm f2.8 STM is a prime lens with fixed focal lenght of 40mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 64mm.