Canon RF lenses have a new feature: a control ring. What is the control ring and what can be done with it?
The control ring is a third ring on the lens in addition to the zoom and focus rings (of course primes lack the zoom ring so they have only two rings: focus and control). The control ring typically has clicked positions, so it adjusts some camera parameter in steps.
As a cost reduction measure, the RF 24-240mm superzoom lens has focus and control ring merged into one: you select the function by using a switch. The ring in this lens lacks clicked positions. As another cost reduction measure, the manual focus switch (which has been replaced by the focus/control switch) is moved to the camera menu in this superzoom lens.
The control ring has a knurled surface allowing to detect it by feel. This applies also to the RF 24-240mm lens: it has a knurled surface too in the merged focus/control ring.
One version of the EF-EOS R adapter to adapt older EF lenses to the camera has a control ring. If this adapter is used, obviously the control ring is the ring closest to the camera. The RF 24-240mm lens has also control ring closer than the zoom ring, but most lenses have it opposite: control ring is the furthest away ring. However, the RF 70-200mm lens has control ring closest to the camera.
The function of the control ring is programmable from camera menu with nine choices:
- Change aperture (only when holding metering button down)
- Change shutter speed (only when holding metering button down)
- Change ISO speed (only when holding metering button down)
- Change exposure compensation (only when holding metering button down)
- Change aperture
- Change shutter speed
- Change ISO speed
- Change exposure compensation
Sometimes the control ring is criticized as being too easy to accidentally change some important camera setting. However, the programmable choices to make it work only when holding metering button down make it rather unlikely this would occur.