It looks like Canon is continuing its R&D into shrinking lenses as much as possible, we have seen multiple patents dealing with the size of lenses, and we’ve seen some small full-frame lenses over the last year such as the RF 28-70mm f/2.8L IS STM and RF 16-28mm f/2.8L IS STM.
It makes sense that Canon would bring similar constant aperture APS-C lenses of small stature. The interesting optical design in this patent is a Canon RF-S 18-50mm f/4 IS STM.
Overview
Problem
To provide a small-sized and lightweight positive lead type zoom lens.
Means for Solving
The zoom lens includes a positive first lens unit L1 that does not move during zooming, a negative second lens unit L2 that moves during zooming, and a subsequent lens unit including one or more lens units. The first lens unit includes four or less lenses.
A thickness on the optical axis from a surface closest to the object side to a surface closest to the image side of the second lens unit is denoted by D2, a sum of thicknesses on the optical axis from the surface closest to the object side to the surface closest to the image side of one or more lenses constituting the second lens unit is denoted by TG2, a focal distance at the telephoto end of the zoom lens is denoted by ft, and a focal distance of the second lens unit is denoted by f2. 3.1 ≤ D2/TG2 ≤ 10 and – 20.0 ≤ ft / f2 ≤ – 6.8 are satisfied.
Canon RF-S 18-50mm f/4 IS
- Focal length: 18.54-52.02
- F-number: 4.10
- Half angle of view: 33.06-14.50
- Image height: 13.66
- Total length: 130.47
- Back Focus: 14.72-14.72
Summary
An RF-S 18-50mm f/4 IS STM is the type of lens that we can see comping to the RF-S line-up of lenses. f/4 will keep it extremely small, and if you want f/2.8, you can go with the RF 16-28mm f/2.8L IS STM.
As always, just because the optical design appears, it doesn’t mean it will ever reach market, but this one makes sense.
Source: Japan Patent Office
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Canon, give us something to replace the EF-S 15-85mm instead. Something covering at least 15-70mm. That is the single most important RF-S lens we are still missing (and that's is objectively a fact ;)).
My take is that it is bloody unlikely that this 18-50 will ever come to light. A non-extending 70-200F4 is more likely, as that is clearly what they're trying to develop here.