Canon’s Latest Lens Patent

credits: Canon

It looks like Canon may be developing a very practical addition to its RF super-telephoto lineup. A newly published patent points to an RF 300mm f/2.8 L IS USM with a built-in 1.4× teleconverter, effectively letting you switch between 300mm f/2.8 and roughly 400mm f/4 without changing lenses. On paper, that is a genuinely useful combination for sports and wildlife photographers who often need a bit more reach but don’t want to juggle extenders or swap glass in the middle of a shoot.

The idea is not entirely new. Nikon has already gone down this road with its Z-mount 400mm f/2.8 and 600mm f/4 primes that include built-in teleconverters, and Canon itself has some history here with the EF 200–400mm f/4L IS USM Extender 1.4×. What is different this time is that Canon appears to be applying the concept to a fast prime rather than a zoom. According to the patent, the extender group sits near the rear of the lens and can be engaged internally, increasing focal length by about 1.4× without changing the lens’s physical length. That means no breaking weather sealing, no exposed sensor, and no interruption during shooting.

Another interesting detail in the diagrams is the apparent focus on balance. The optical layout suggests the weight is pulled toward the rear of the lens, which should help when shooting handheld or off a monopod. Canon also currently doesn’t offer an RF 300mm f/2.8 at all, so a lens like this would fill a gap below the bigger 400mm and 600mm options that tend to be very large and very expensive.