The Canon RF 100-500mm f/4.5-7.1L IS USM is a highly respected lens, offering some of the company's best performance and image quality, but at nearly $3,000, it is a rather expensive option. The RF 100-400mm f/5.6-8 IS USM offers a similar focal length range at a price not even a quarter that of the 100-500mm, making it an intriguing alternative. How does it hold up? This great video comparison takes a look at both lenses to help you decide.