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Several new catadioptric designs (commonly referred to as “mirror” lenses) appeared in a patent application to Japanese authorities, including a 1200mm f/8 and an 800mm f/5.6.
First called out in a post on An Image on a Sensor, the embodiments show typical “mirror lens” construction, but with a larger-than-typical number of lens groups and elements extending from the mirror optical tube, back toward the sensor.
This may imply a much higher level of aberration correction than is normal in this type of lens. Most catadioptric lenses built for cameras are attempts to get at large focal lengths as cheaply as possible, and the catadioptric design allows for more light gathering with less glass.
And they typically have less length, too. Because the mirror design causes the light to double-back on itself a couple times, these lenses are shorter than other types of designs. The 800mm f/5.6 embodiment of this new patent application, for example, has a lens length of only about 13 inches. Lenses typically add a little bit of length in actual production, but this 800mm lens would likely appear as an extremely-wide lens about the length of the old EF 70-200 f/2.8, with perhaps an inch or two added.
Canon had a range of mirror-based lenses previously.