Canon Patent Application: Curious Catadioptric Optical System

Usually I dismiss these catadioptric lenses when they come up because Canon hasn't really done anything with these in modern times (the last Canon catadioptric lens was back in the FD days).

The nature of catadioptric is that they have a very small aperture, made even smaller by the corrector mirror sitting at the front of the lens, which also gives catadioptric lenses their "signature" donut bokeh.

But there are other applications for these lenses, which is why we may be seeing a slew of patent applications for, which is Canon's forays into imaging satellites.  Having a compact high focal length lens for satellite imaging would be an excellent use case.

What I found curious about these embodiments is the location of the elements. The first group of elements is deep inside of the catadioptric lens itself - which is very unusual.

I think in this case Canon is attempting to improve on Maksutov designs and trying to make an even smaller catadioptric lens.

This catadioptric lens also has a complex field correction, possibly because they have massively shortened the distance between the front of the lens and the mirror (M1) and also the distance between M1 and M2.  Shortening the distance significantly usually has a bearing on aberrations and coma performance.  In normal catadioptric telescopes, you need field flattener optics to get good performance across the image circle. The optics we see, are adding more corrections for aberrations and providing good performance across the image circle.  It's pretty neat.

the present invention provides a catadioptric system capable of achieving good imaging performance in a compact configuration and an image pickup apparatus having the same.

According to the present invention, it is possible to provide a catadioptric system capable of achieving good imaging performance and an image pickup apparatus having the same in a compact configuration

Will we see this on the RF mount, etc? I doubt it.  I think this if it ever comes out will be for Canon's forays into scientific applications.  I would love for Canon to come out with an actual telescope though.

Japan Patent Application 2022-045962