That's what a Canon patent application seems to suggest, a 300mm f/2.3 mirror lens. Read…
Very interesting patent for 15-43mm f/2-4 lens for APS-C sensors that may point to the upcoming Canon Powershot G1 X Mark III camera, rumored to have an APS-C sensor.
- Zoom ratio: 2.74
- Focal length: 15.65 29.18 42.90
- F No.: 2.06 2.99 4.00
- Half angle: 41.12 25.09 17.66
- Image height: 13.66 13.66 13.66
- Back focus: 8.52 8.01 7.20
Patent literature is hard to grasp. Any help is welcome.
In a zoom lens from which an interval of a lens group which comprises the 1st lens group of negative refracting power, the 2nd lens group of positive refracting power, the 3rd lens group of positive refracting power, the 4th lens group of negative refracting power, and the 5th lens group of positive refracting power, and is adjacent to on the occasion of zooming arranged in order from the object side to the image side changes, between said 2nd lens group and the 3rd lens group, have an aperture diaphragm and said 4th lens group moves on the occasion of focusing — said 4th lens group — most — a curvature radius of a lens surface on the object side — a time of setting a curvature radius of a lens surface on the image side to R4b most of R4a and said 4th lens group, 0.2<(R4b+R4a)/(R4b-R4a)<3.0 A zoom lens satisfying a becoming conditional expression.
[via Hi Lows Note]