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.
The patent drawing does have a lens group labeled "Lis" - Lens Image Stabilization perhaps?
Lens group "Lfo" Lens Focus perhaps?
Patent: Is Canon planning to release catadioptric (mirror) super telephoto lenses?
Canon Support for EOS C70 | Canon U.S.A., Inc.
Tig to Stig: that's a good find. I saw that too. This is a different set of patents, the biggest difference being that these new ones appear to be more an attempt at a higher-end image quality. Those earlier patent designs show almost no correction, and the "sea grass" graphs show very poor edge aberrations.
(bad contrast, low resolution to the edges, "halo" in the center, bad bokeh).
They had the brilliant EF400mm f5.6L. Light, superb optics, and affordable. The closes they have now is the 100-500mm zoom, which I'd always use on the tele end, unnecessarily heavier, more expensive. And f7.1.
Really wish they come up with the something like the Sony 200-600mm. Serious stuff but not costing as much as a sedan.
The compact cameras market is practically gone, and ILC camera market is shrinking quickly. Smartphone cameras are getting better, including focal length, e.g. Samsung's moon zoom on Galaxy S2x, though I'm not going to argue for the image quality*. One way to increase the pie is getting cheap small lenses that offers abilities not available till now, such as the RF 16mm which requires correction on a computer, and long focal mirror lenses.
I wouldn't bet too much money on this patent becoming a lens, but I understand the motivation.
* If anyone wants to compare, I can shoot the moon with an S21 on the weekend, or when its full on April 16th, and share the images.
Surveillance, why not, but only if being visible doesn't matter. Definitely no lenses for spying activities... ;)
It's inherent with catadioptric designs, AFAIK there's no way to hide or minimise the effect.
Personally I'd *much* rather Canon brought out a lightweight "telescopic" 800mm F8, along similar lines to the RF 600mm F11 and RF 800mm F11 designs. Such a lens would probably be cheaper and lighter than this catadioptric 800mm F5.6, it wouldn't have ugly bokeh, and it would be far more useful for bird photography.
It would be interesting to know which of these designs would appeal most to sports photographers - 800mm F5.6 catadioptric, or 800mm F8 telescopic?