Most of us have read that one of the intrinsic advantages of mirrorless cameras is that lens mounts with a larger diameter and a shorter distance to the sensor – which mirrorless camera design has enabled – have the potential to be either optically superior, or cheaper to manufacture, or a bit of both.
Canon has now produced a four-minute video (above) which clearly explains why it is so. Naturally, it is promoting the virtues of its own mirrorless RF lenses, but the principles apply to other brands’ mirrorless cameras and lenses as well, so the video is worth watching whatever camera system you favour. In fact Canon has a ‘flange focal distance’ (distance from rear lens element to the sensor) slightly longer than Sony and Leica and even longer still than the Nikon Z system.
The video claims RF lenses ‘deliver higher image quality and high spec performance in more compact designs.’ But while lens aberrations are reduced with large-throated, small-flanged lenses, flare and ghosting are more of a challenge than they have been with DSLR lens design. The video states that sophisticated lens coatings are employed to minimise this problem.
The video also refers to the added electrical contacts built into RF lenses, which provides increased bandwidth and power to and from the lens.
…Then comes the reality check. In the same week Canon released its video, DxOMark released its analysis of the $3300 RF 50mm f1.2 L USM lens, the first Canon RF lens to undergo DxO bench-testing, and it seems somewhat mediocre considering the asking price. (And, weighing just under a kilo and 108mm long, not that compact.) neither.) While it does score well on the measure of chromatic aberration, a total score of 38 brings it in way down from the top lenses as pronounced by DxOMark: the top lens with a score of 51 is the Sigma 85mm f1.4 Art lens on a Nikon D800E body. The new RF 50mm is not even in the ‘Lens Top 40’, but then again, no other Canon lenses make it into this exalted company, neither.
Below are the Top 10 Canon lenses as rated by DxOMark: