The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon RF-S 7.8mm F4 STM Dual and the Canon RF-S 3.9mm F3.5 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 RF-S 3.9mm F3.5 is the longer of the two lenses at 55mm. The Canon RF-S 7.8mm F4 STM Dual with a length of 42mm, is 13mm shorter. Besides being longer, the Canon RF-S 3.9mm F3.5 also has a larger diameter of 112mm compared to the Canon RF-S 7.8mm F4 STM Dual'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-S 7.8mm F4 STM Dual weighs 131g, which means it is 159g (54%) lighter than the Canon RF-S 3.9mm F3.5 which has a weight of 290g.
Filter Threads
The Canon RF-S 7.8mm F4 STM Dual has a filter size of 58mm whereas the Canon RF-S 3.9mm F3.5 has a 31mm 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 RF-S 7.8mm F4 STM Dual:
And these are the 31mm filters that we recommend for the Canon RF-S 3.9mm F3.5:
Lens Mounts
Both the Canon RF-S 7.8mm F4 STM Dual and the Canon RF-S 3.9mm F3.5 has the same Canon RF lens mount. Some of the latest released cameras that are compatible with the Canon RF lenses are Canon R50 V, Canon R100 and Canon R50.
Focal Range
Canon RF-S 7.8mm F4 STM Dual is a prime lens with fixed focal lenght of 7.8mm which has an effective (full-frame 35mm equivalent) focal range of
12.8mm when used on a APS-C / DX format camera.
On the other hand, the Canon RF-S 3.9mm F3.5 is a prime lens with fixed focal lenght of 3.9mm which has an effective (full-frame 35mm equivalent) focal range of 6.4mm when used on a APS-C / DX format camera.
