SA Control Ring
The goal of macro photography is to capture images of subjects up close, so background blur, or bokeh, is produced by adjusting the aperture instead of the subject's distance. Canon wanted to give users more creative freedom in creating unique bokeh effects when taking macro photos.
Canon recognised that the same principle could be used to adjust spherical aberration (SA), which led to the development of the SA control ring. Spherical aberration was previously regarded as a speciality lens feature that only served to reduce overall image quality. Canon overcame this stereotype by developing a dedicated control for controlling spherical aberration with high precision, allowing users to achieve softer or harder bokeh effects.
When Canon set out to design an RF Mount successor to the EF100mm f/2.8L Macro IS USM lens, which was a favourite among macro users, the optical design of the EF100mm f/2.8L Macro IS USM allowed it to be the first Canon lens to incorporate the SA control ring. This macro lens design has a maximum magnification ratio of 1.4x (which exceeds the EF model's 1.0x magnification performance) and is also highly compatible with the SA control ring due to its floating lens system.
This introduces new functionality for adjusting the character of the bokeh effect, resulting in soft focus or bubble bokeh (hard bokeh) effects similar to those of older lenses, whether shooting at macro or normal distances. Users can adjust the softness of the subject in focus by rotating the SA control ring on the lens barrel. This is useful for both macro and portrait photography. The SA control, along with the ability to adjust the bokeh effect, allows macro and portrait users to express themselves in ways that no previous Canon lens has.