Canon has their DO (Diffractive Optics) technology[1] which I think only ever made it into a 70-300[2]. Mirror lenses have been around for a long time. They fo

Canon has their DO (Diffractive Optics) technology[1] which I think only ever made it into a 70-300[2]. Mirror lenses have been around for a long time. They fold the length of larger telephotos into about a third with some trade-offs in speed and image quality. [1] https://global.canon/en/v-square/34.html https://global.canon/en/v-square/34.html [2] https://www.usa.canon.com/internet/portal/us/home/products/details/lenses/ef/telephoto-zoom/ef-70-300mm-f-4-5-5-6-do-is-usm https://www.usa.canon.com/internet/portal/us/home/products/d...