The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 24mm f2.8 IS USM and the Canon 20mm f2.8 USM 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 20mm f2.8 USM is the longer of the two lenses at 71mm. The Canon 24mm f2.8 IS USM with a length of 56mm, is 15mm shorter. Besides being longer, the Canon 20mm f2.8 USM also has a larger diameter of 78mm compared to the Canon 24mm f2.8 IS USM'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 24mm f2.8 IS USM weighs 280g, which means it is 125g (30%) lighter than the Canon 20mm f2.8 USM which has a weight of 405g.
Filter Threads
The Canon 24mm f2.8 IS USM has a filter size of 58mm whereas the Canon 20mm f2.8 USM has a 72mm 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 Canon 24mm f2.8 IS USM:
And these are the 72mm filters that we recommend for the Canon 20mm f2.8 USM:
Lens Mounts
Both the Canon 24mm f2.8 IS USM and the Canon 20mm f2.8 USM 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 24mm f2.8 IS USM is a prime lens with fixed focal lenght of 24mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of
38.4mm.
On the other hand, the Canon 20mm f2.8 USM is a prime lens with fixed focal lenght of 20mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 32mm.