Canon Patent Application: Canon Mirrorless 8-15mm Fisheye Zoom

This Canon patent application is for a fisheye zoom. It's an interesting patent application because it also goes through the mechanics of a fisheye lens, from the changes that occur to the image size to make the fisheye look circular in the camera image.

Canon mostly appeared to be working on quick focusing of this lens by moving as much of the heavier and bigger elements as they could to the back of the lens.

In order for a zoom lens to have a wide angle of view and achieve high optical performance across the entire zoom range and the entire object distance range, it is important to appropriately set the elements constituting the zoom lens. For example, it is important to appropriately set the zoom type (the number of lens units and the refractive power of each lens unit), the lens configuration, and the lens unit selected for focusing, and so on. 

If these configurations are not appropriate, achieving a wide angle of view will increase the size of the whole system and also increase the variations of various aberrations caused by zooming and focusing. It will therefore be difficult to achieve high optical performance across the entire zoom range and the entire object distance range. 

For example, for a fisheye zoom lens having an imaging half angle of view of 85 degrees or more, a meniscus lens having an extremely strong negative refractive power needs to be disposed closest to the object side within the first lens unit in order to take light rays into the zoom lens from such a wide angle of view. Generally, lenses in a first lens unit not only have strong refractive powers but also have large effective diameters. Thus, when it comes to a fisheye zoom lens, its first lens unit is heavy and large as well. Then, if the entirety or part of the first lens unit (the closest lens unit to the object side) is used as a focus lens unit, quick focusing will be difficult. 

This is also a patent application for most likely the EF-M *OR* the RF mount because the backfocus (BF) values are well under 44mm, and the image sensor they show in the sub-pictures is an APS-C and another diagram showing the image circle for full frame.  Also in the two embodiments, the maximum image height is 13.50mm, APS-C, in one example, and 21.64mm in the other, full frame, example.

Given the fact that this focal length has shown up for full frame EF mount, it's probably more likely that it's for the RF mount as an actual developed lens, than it would for the EF-M mount.

APS-C Embodiment:

Focal length             5.30   9.51
F-number                 3.50   3.50
Angle of view (degree) 181.00 182.00
Image height             7.50  13.50
Total lens length       77.28  69.52 
BF                      11.09  16.77

Full Frame embodiment:

Focal length             8.01  15.30
F-number                 3.78   4.60
Angle of view (degree) 177.30 183.10
Image height            11.15  21.64
Total lens length      105.23 103.57
BF                      12.00  28.46

US Patent Application 20190094490