If you're looking for a long telephoto lens for the mirrorless R system, Canon has some great options available. The RF 200-800mm f/6.3-9 IS USM is the most recent one, and I predict it will become a very popular lens. And it's with good reason. If you ignore the extremely expensive long telephoto prime lenses in the Canon R-series, there are three lenses to choose from. One of those is the beautiful and versatile RF 100-500mm f/4.5-7.1L IS USM, a lens that covers a large focal length range, making it useful for both landscape photography and wildlife photography.
Canon RF 200-800mm & RF 24-105
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Canon RF 200-800mm F6.3-9 IS USM Review