100-400mm f/4.5-5.6 lenses have long been popular among sports, bird, and wildlife photographers for offering a very useful focal length range in tandem with maximum apertures that balance performance, bulk, and price. For Fujifilm shooters, there is the XF 100-400mm f/4.5-5.6 R LM OIS WR, and this excellent video review takes a look at the sort of performance and image quality you can expect from it in practice.