Buyer checklist
How We Compared These Canon RF Lenses: RF or RF-S Is the Decision, and It Is Not Reversible
These five are real Canon products, so unlike most of what we compare, the specifications come from a manufacturer that publishes them: every figure below is from Canon's own listing copy, which states focal lengths, maximum apertures, stabilisation stops, minimum focusing distances, maximum magnifications and filter thread sizes precisely. We checked each against the Amazon detail tables and found the tables badly unreliable, with unit conversions mangled into 10.5 centimetres for a 105mm focal length, 40 centimetres for 400mm, 6.7 centimetres for a 67mm filter thread and a maximum aperture given as 50 millimetres on a 50mm lens. We have worked entirely from Canon's bullets and ignored the tables, and we would advise the same. We also found the same lens, Canon part number 4111C002, listed under two separate ASINs at prices roughly seventy dollars apart, which is flagged in its section. Nothing here was mounted, focused or tested by us; the stabilisation stop figures in particular are Canon's own ratings, not measurements of ours.
Canon RF Lenses: RF or RF-S Is the Decision, and It Is Not Reversible Buying Questions
What is the difference between RF and RF-S?
The size of sensor the lens is designed to cover. RF lenses project an image circle large enough for a full-frame sensor and work on every EOS R body. RF-S lenses project a smaller circle sized for Canon's APS-C sensors, which is how they are made lighter and cheaper, and they fit the R7, R10, R50, R100 and similar. Both use the identical physical mount, so an RF-S lens will attach to a full-frame body, and Canon is explicit about what happens next: the camera automatically switches to APS-C crop mode, so you shoot with roughly 40 percent of your sensor. The lens is not damaged and the photos are not broken, you just paid for a full-frame camera and are not using it.
How do image stabilisation stops add up?
Lens-based optical stabilisation and a camera's in-body stabilisation can cooperate, and Canon publishes both figures where they do. The RF 100-400mm is rated at 5.5 stops on its own and up to 6 stops when paired with an EOS R body that has IBIS. The RF-S 18-150mm is rated at 4.5 stops alone and up to 6.5 stops with IBIS. Note that the combined figure is not the sum: the two systems overlap rather than stack arithmetically. What a stop means practically is a doubling of the shutter speed you can hand-hold, so 5 stops is the difference between needing 1/125 and getting away with 1/4 on a static subject. It does nothing for a moving subject.
Which of these should be a first lens?
The RF 50mm F1.8 STM, for most people, and the reasoning is about the aperture rather than the focal length. A kit zoom at f/4 to f/7.1 struggles indoors and produces flat backgrounds; an f/1.8 prime gathers far more light and separates a subject from its background in a way no variable-aperture zoom in this group can. The cost is that you zoom with your feet. If you would rather have one lens that covers everything and are shooting mostly in daylight, the 24-105 is the honest answer instead, and on an APS-C body the RF-S 18-150 plays that role.