The Canon RF 100-400mm F5.6-8 IS USM ($649.99) is an ideal lens for photographers interested in capturing telephoto subjects—such as wildlife, team sports, and other distant action—but who aren’t able to afford the pro-grade RF 100-500mm F4.5-7.1 L IS USM ($2,699). The 100-400mm offers enough zoom power that you can snap shots of backyard critters, while remaining light enough for walks and travel. You miss out on some L series features such as weather sealing, but images are sharp, the autofocus is sound, and its stabilized optics make handheld photography easy. The RF 100-400mm is another strong midrange entry for creators using the EOS R system.
Midrange Telezoom
The RF 100-400mm measures 6.5 by 3.1 inches (HD) and weighs a mere 1.4 pounds; both are very reasonable given its full-frame coverage and telephoto reach. Its construction is decidedly mid-grade—Canon uses sturdy polycarbonate (not cheap plastic) for the barrel and tolerances are tight all around. You miss the weather protection, anti-smudge fluorine glass, and metal construction from the 100-500mm L, but you’re also not paying nearly as much.
As mentioned, the lens is a welcome compromise for photographers who want to try their hand at telephoto work, but don’t have the budget for an L series zoom. It joins a couple of collapsible prime lenses with longer focal lengths, the RF 600mm F11 IS STM and 800mm F11 IS STM, in Canon’s lineup of low-cost telephoto lenses.
The RF 100-400mm features the most typical design of the three—the RF 600mm and 800mm use funky retractable designs and the 800mm especially can be unwieldy to handhold. The 100-400mm doesn’t feel front-heavy, even with its inner barrel fully extended to 400mm. Canon doesn’t offer a tripod collar, but I didn’t find one necessary—the Peak Design Travel Tripod has no problem supporting the EOS R5 with the lens zoomed to 400mm.
Canon doesn’t include a lens hood in the box, but sells the ET-74B accessory hood for $44. It’s a worthwhile investment if you’re worried about bumping the front glass and offers a bit of extra flare suppression, but the Super Spectra anti-reflective does a good job on its own—I didn’t use the hood while testing and didn’t miss it. If you prefer a protective filter, the lens takes the 67mm thread size.
Handling and Autofocus
The RF 100-400mm sports three separate control rings—zoom, focus, and function—along with control switches to swap the focus mode and toggle optical stabilization. The zoom and focus rings have a rubber covering with raised ridges, whereas the function ring is bare polycarbonate with a diamond-textured pattern.
The zoom ring requires just a little bit of torque to turn, enough to move the inner barrel in or out. The focal length stays put once set, a good thing, and the inner barrel doesn’t creep out on its own when facing downward. A zoom lock switch keeps the lens set at its shortest 100mm focal length when engaged.
A silent USM focus motor drives autofocus. With the EOS R5, the lens snaps from close-up to distant focus in an instant and is quick enough to track moving subjects. Manual focus is an option too, with both nonlinear and linear responses available. The RF 100-400mm is a strong option for videographers as well—the lens doesn’t exhibit any visible focus breathing, so you can use it to get rack focus shots without any distracting change to the angle of view.
The control ring’s function is flexible—I use it as an EV control, but you may find it more useful to swap between different focus modes, set the aperture, or fine-tune white balance. It clicks as it turns, so you always know how much of an adjustment you make. You can swap the ring to silent, click-free operation for a $79.99 fee at a Canon service center.
Long lenses often sacrifice macro capability—they’re made for far-off subjects, not close ones. The RF 100-400mm focuses as close as 3.4 feet (1m), good enough for a decent 1:2.4 life-size magnification rating.
The lens also features image stabilization, a plus if you pair it with an EOS R or RP model that doesn’t offer IBIS. Canon rates the lens for about 5.5 stops of correction with these models and 6.0 stops for IBIS models like the EOS R5. On the R5, I managed blur-free 400mm handheld images at speeds as long as 1/4-second and, with extreme care, even took some sharp 1/2-second exposures.
Strong stabilization is important given the narrow aperture. At f/8 when zoomed in, the 100-400mm is best suited for working outdoors—you need to use a higher ISO or longer shutter speed for shots in dimmer artificial light. Here the stabilization is good enough to make subject motion more of a concern than handshake.
You can add a teleconverter to get a bit more zoom power. With the TC 1.4x, the lens turns into a 140-560mm F8-11 and, with the TC 2.0x, it’s a 200-800mm F11-16. At $500 and $600 respectively, a teleconverter is a pricey add-on for the lens and an accessory that works best in bright environments.
RF 100-400mm: In the Lab
I paired the 100-400mm with the 45MP EOS R5 for lab testing using Imatest software. Optical performance is good wide open, with excellent resolution toward the center (4,100 lines), good performance through much of the frame, and some softness at the edges throughout its zoom range.
If you’re working in bright conditions, narrow the f-stop a little more for the crispest results. Central resolution hits outstanding marks at 100mm f/8 (4,600 lines) and settles into very good results (3,700 lines) as you move off-center. Image quality holds up when zoomed in—we tested the lens at 100mm, 250mm, and 400mm focal lengths—but remember that since the maximum aperture drop as you zoom, you get sharper details at 400mm f/11 than at 400mm f/8.
Lateral chromatic aberration—color fringing—shows up in uncorrected Raw images, but isn’t a concern when working in JPG format. Raw processing software takes care of the false color easily—in Adobe Lightroom Classic you just need to make sure to check the Remove Chromatic Aberration option. Canon’s JPG corrections also remove some pincushion distortion and a modest vignette at the widest aperture. Adobe includes a one-click Raw correction profile that matches Canon’s in-camera corrections.
Telephoto lenses, even ones with a narrow aperture, are capable of blurring backgrounds behind subjects. The 100-400mm draws pleasing background bokeh with mostly rounded, soft-edged highlights. Some cat’s eye shape highlights are visible at the edges of the frame when using the lens with its aperture wide open, but the rounded 9-blade diaphragm draws circular highlights across the frame when you stop it down.
Best Used Under the Sun
The Canon RF 100-400mm F5.6-8 L IS USM should appeal to photographers who are shopping for a telezoom, but aren’t ready to step up to a high-end L series option. You miss out on a few pro features—the RF 100-400mm doesn’t include dust, splash, or anti-smudge fluorine protection—but you still get crisp photos, speedy focus, and quality materials here.
Canon opted for a relatively narrow aperture to meet the RF 100-400mm’s form and price. It’s a path the company has walked down for other RF lenses, including the slim 24-105mm F4-7.1 IS STM. Full-frame digital cameras do a very good job at the higher ISO settings necessary to freeze motion under dimmer light, however, so this is a sensible trade-off, especially for a long lens that works best in wide, open spaces. If you’re looking for a lens for indoor sports, consider the RF 70-200mm F4 L IS USM or, if you can afford it, the 70-200mm F2.8 L IS USM.
If you’re after an affordable lens to snap shots of wildlife, pets at play, team sports, and other traditional scenes, the RF 100-400mm excels. Third parties haven’t jumped on board to support the RF system yet, so your only alternative is to adapt EF-mount lenses. If you’ve already got the EF-EOS R adapter, the Sigma 100-400mm F5-6.3 or Tamron 100-400mm F4.5-6.3 are brighter alternatives, but both are also heavier and more expensive (around $800 each).
The RF 100-400mm is a practical choice for RF owners who want more reach than the 24-105mm kit lens delivers. You should consider the funky RF 600mm F11 IS STM if you’re primarily interested in wildlife, as its longer focal length comes in handy when photographing smaller subjects at distance. But we think more photographers will find the 100-400mm’s compact design, zoom lens convenience, and traditional handling a bit more welcoming.
