Focal length is used to determine your lens's angle ... as it's particularly suitable for portraits and close-up photography.

Venus Optics, makers of Laowa lenses, has built up quite a reputation for probe lenses: long macro lenses that can help you ...

This will extend the focal length from the 400mm equivalent ... be further enhanced using a third-party close-up lens/filter if close-up/macro photography is something you enjoy.