What is the patent number of Canon wide-angle lens?

Some explanations are incomplete.

First of all, 50MM fixed focus is close to the naked eye, but it doesn't mean there is no distortion, which is what you said.

In addition, when the 35MM fixed focus is installed on APS-C frame machine, it should be multiplied by the lens conversion ratio and converted into the equivalent focal length, but the physical properties remain unchanged.

For example, your 35MM lens, if the quality of controlling wide-angle distortion is not high, does not mean that the distortion will disappear when it is installed on APS-C frame machine. It is only equivalent to the 56MM viewing angle of a 35MM film machine, and nothing else has changed, and the physical properties have not changed.

Canon SLR with wide-angle lens can be considered as 10-20MM, 16-35MM, SIGMA 10-20MM in the sub-factory, T 12-24 and so on.