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Canon RF 100-400mm F5.6-8 IS USM: What to Know
This is the reach lens, and what makes it notable is how little it asks in exchange. Canon describes it as a compact, lightweight telephoto zoom, which for a 400mm lens is a meaningful claim: conventional 400mm optics are large, heavy and expensive, and they are why most people never own one. The compromise Canon chose is aperture, f/5.6 at 100mm falling to f/8 at 400mm, and that single decision is what shrinks the lens and the price.
The stabilisation and autofocus are both proper rather than budget. Optical Image Stabilizer is rated at up to 5.5 stops on its own, and up to 6 stops paired with an EOS R body that has in-body stabilisation, which is what makes 400mm handholdable at all. Autofocus is Nano USM, Canon's fast and quiet system rather than the slower STM used on the cheaper lenses here, and at 400mm on a moving subject focus speed is the difference between a photograph and a blur.
The close-focus figures are better than expected for a telephoto: a minimum focusing distance of 2.89 feet at 200mm and a maximum magnification of 0.41x at 400mm. Nearly half life size from a telephoto zoom means it doubles as a working lens for insects and flowers at a distance that does not scare them off, which a true macro lens cannot do.
Be clear-eyed about f/8. At 400mm in anything less than good light, f/8 forces high ISO, and stabilisation will not help a bird in flight because the motion is the subject's. This is a daylight wildlife, sport and aviation lens. In poor light the honest answer is that the fast telephotos that solve this problem cost several times as much and weigh several times more, which is precisely why this lens exists. The filter thread is 67mm, matching the 24-105 above.
Key Listed Features
100 to 400mm zoom range in a body Canon describes as compact and lightweight for the class
Up to 5.5 stops of optical image stabilisation, rising to up to 6 stops with an IBIS-equipped EOS R body
Nano USM autofocus for fast, quiet focusing rather than the slower STM used on cheaper RF lenses
Minimum focusing distance of 2.89 ft at 200mm with maximum magnification of 0.41x at 400mm, on a 67mm filter thread
