Canon has published a pretty interesting optical design patent for large aperture zoom lenses. The two designs in this patent are pretty interesting.
Canon's goal in this patent
To provide a zoom lens having a short total length and a small size but having high optical performance, and an image pickup apparatus having the same.
As you can see, these lens designs use the “reverse” zoom design like the original EF 24-70mm f/2.8L USM. This probably helps in reducing the length and size of the lens. As you can see, the image height changes when zooming in and out.
Overall length is quite impressive at 105.42mm (about 4″) at the wide end. Keep in mind that those measurements are from the image sensor to the front element of the lens design.
Example 1
- Focal length: 28.84mm – 67.90mm
- F-number: 2.91
- Half angle of view: 32.68° – 17.67°
- Image height: 18.50mm – 21.64mm
- Overall length: 138.40mm – 105.42mm
- Back focus: 10.97mm – 21.12mm
Example 2
- Focal length: 28.84mm – 60.00mm
- F value: 2.91
- Half angle of view: 32.68° – 19.83°
- Image height: 18.50mm – 21.64mm
- Overall length: 132.38mm – 106.85mm
- Back focus: 13.47mm – 23.82mm
-Brian
Such a lense could cover 16:9 in fullframe or the entire image of an S35 area.
-Brian
There was a recent front page post claiming a new set of patents were APS-C 'pancake' primes, based on an image height of 18.2mm. It turns out that the patented 16/2.8 in that post is not a new APS-C pancake lens, but rather is the existing RF 16mm f/2.8 lens that you can buy today (which isn't a pancake, but the length in the patent is consistent with the length of the production lens).
The closest is actually APS-H, not APS-C. These are full frame RF lens designs. Consider what we know of Canon – is it more likely they'd make a lens with a larger image circle than necessary, or a smaller image circle than necessary that gets corrected by software (along with forcing that correction in-camera and in DPP)? The latter, of course.