4. Built for the toughest conditions
Both the RF 400mm F2.8L IS USM and RF 600mm F4L IS USM are built to Canon's exacting L-series standards in order to withstand the rigours of professional use. Not only that, but because the lenses are the lightest in their class, they offer huge benefits for photographers who use them regularly.
"The people using this type of lens tend not to be fair-weather photographers," explains Mike. "They are shooting in the cold, in high temperatures, when it's very wet or very dry. These lenses are designed to work everywhere, from the Antarctic to the Sahara."
One issue that can affect objects such as large telephoto primes when they are exposed to high temperatures is thermal expansion and contraction. "Basically, the lens moves a little – just a few microns, but that's like shifting your focus," explains Mike. "Because we made the lenses lighter, we had to improve the thermal efficiency because there is less mass to absorb the heat."
To overcome this issue, Canon designed a two-layer barrel structure, used in both lenses, to reduce the chance of heat being passed through to the inner elements. In addition, the lenses also feature a new type of thermal coating. "It might just look like white paint, but there is a lot of technology within it," says Mike. "It's a heat-resistant paint that reflects UV light to reduce the temperature of the lens."