Super-telephoto lenses are known for being two things: Heavy and expensive. But the new Canon RF 600mm f/11 is neither. With Canon’s full-frame mirrorless cameras in mind, it weighs a hair over 2 pounds and costs just $699, a far cry from the 6.7-pound, $13,000 Canon EF 600mm f/4 for DSLRs. For photographers without the budget of a news agency, a prime lens of this focal length is usually off-limits.
Much of the RF 600mm’s cost-cutting is right in the name, where we see the aperture is stuck at a very closed down f/11. Compared to the EF 600mm, that’s three stops darker, a significant difference (each stop lost reduces the amount of light by half). That smaller aperture means every glass element within the lens can be made smaller, drastically reducing both cost and weight. But there’s a big drawback: While at f/4 you could continue shooting well into the blue hour if you don’t mind bumping up the ISO, at f/11 you basically have to pack your bags before sunset. (The RF 600 is also a fixed f/11; there is no aperture diaphragm, so it can’t be stopped down further.)
That’s not the only thing Canon did to keep costs down. In its latest lens teardown, Lensrentals, a camera gear rental and repair facility, revealed the secrets of the RF 600mm’s construction. Spoiler alert: Lensrentals found aspects of the lens that were surprisingly complex, leading the company to decide not to perform in-house repairs of this lens in the future.
But what makes the lens so cheap is far less surprising: Plastic. There’s a lot of plastic used in the construction, but Lensrentals drew special attention to the mount. While the bayonet itself is metal, it connects to a plastic base via seven screws, a higher-than-usual number apparently due to the fact that they’re going into plastic.
That’s not to say the RF 600mm f/11 doesn’t have redeeming technical qualities. It achieves its remarkably small size thanks to “gapless” diffractive optics, a type of glass element that drastically reduces the total number of elements needed. Canon uses this technology in a number of high-end lenses, as well.
Still, this remains a budget lens that isn’t going to win awards for sharpness, as evidenced by the “not very good” MTF chart, as Lensrentals put it. MTF charts are a measurement of optical resolution, a key factor in determining the overall resolution your camera can capture. That’s OK, though, as the RF 600mm serves a different purpose, to bring super-telephoto imaging to photographers who otherwise don’t have the money or the space to do so.
