Canon RF 100-400mm F5.6-8 IS USM Lens Review

The lightweight, affordable telephoto zoom lens game was just changed.

Large size, heavy weight, and high prices have been synonymous for Canon zoom lenses reaching to 400mm, but the Canon RF 100-400mm F5.6-8 IS USM Lens changes that equation. The RF 100-400 costs less than 25% as much as the previous RF zoom lens that includes the 400mm focal length (the RF 100-500), and it weighs less than half as much as that lens.

Firsts are usually fun, and the RF 100-400 is Canon's first consumer-grade zoom lens to reach longer than 300mm. While Canon has long included 100-400mm lenses in their lineup, the RF 100-400 is the first such lens to lack the professional grade "L" moniker and the amenities that lens class brings.

With a narrow max aperture, this lens is not fast. However, the Canon RF 100-400mm F5.6-8 IS USM Lens is exceptionally compact, lightweight, and affordable. So strong are these advantages that even professionals may want to have this lens option available in their kit.

Focal Length Range

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Choosing the right focal length or focal length range is the first key to selecting the right lens because the focal length determines the perspective and scene framing combination. With a range that starts at 100mm (short telephoto) and goes to a super-telephoto 400mm (before adding extenders/teleconverters), this lens covers a huge range of uses, including many general-purpose telephoto needs. When out shooting, I usually have a lens covering the 100-400mm range in the bag.

One of the best uses for the 100-400mm focal length range is wildlife photography. Large or close wildlife can be contained in the frame at the wide end of the range, and environmental portraits can also be created. From the other perspective, when the wildlife is scared of you (or vice versa) or you cannot or do not want to approach more closely, 400mm permits capturing images of distant subjects rendered large in the frame.

Smaller birds and animals, chipmunks for example, often need longer focal lengths to have a substantial size in the frame even at close distances. These subjects are included on this telephoto zoom lens's uses list. The RF 100-400 is a good zoo and safari lens option.

A 100-400mm lens is often a great choice for photographing people. The wider focal lengths are especially ideal for portrait photography, including indoors, as long as adequate ambient light is available or flash is utilized. The mid and long focal lengths, typically most easily used outdoors, will provide a more compressed appearance (due to the longer subject distance), and these focal lengths bring the potential for a strong background blur (long focal lengths magnify the background blur). Parents chasing kids can find plenty of uses for this entire focal length range, including for their at-the-park and at-the-beach needs. This focal length range is ideal for headshot portraits.

People participating in sports make great subjects for the 100-400mm focal length range. While a long telephoto lens is a good choice for sports from a safety perspective (safety both from and for the subject), it is also a good choice when there is a physical or designated barrier to getting closer, such as a fence or the perimeter lines on a sports field. Sometimes, the action can be close, and sports photography needs can range all of the focal lengths this lens avails. A full-frame camera-mounted 400mm lens will reach into large field events, covering a substantial portion of even large soccer, football, field hockey, lacrosse, etc. fields, and close action can be contained in the frame at 100mm. That a zoom range (vs. using a prime or single focal length lens) facilitates ideal in-camera framing of a subject over a wide range of distances results in full use of your camera's imaging sensor, creating optimal image quality.

All of the focal lengths in this lens are useful for landscape photography. It is often easy to create attractive, compressed-perspective landscape images when using a telephoto lens.

Note that long focal lengths can make even a mediocre sunrise or sunset look amazing. This lens is a great choice for smaller flora, such as the flowers in your garden.

Wildlife, sports, and landscape photographers will make up a large percentage of the owners of this lens, but there are plenty of other uses for this wide 4x focal length range. Photojournalists, especially those with restricted access to their subjects, may find this focal length range useful. With the close minimum focus distance, this lens will work excellently for product photography. A 100-400mm lens is a good choice for air shows.

Sometimes, laziness (perhaps "relaxation" sounds better) is a good reason to use the 100-400mm focal length range. Sit in the comfort of your car, avoid the need to cross a creek, stay back from the surf, etc. Another benefit of having the wider focal lengths available is that photos can be framed appropriately from in front of line-of-sight obstacles.

I've only touched on a small percentage of the uses for this lens. If I am not using it as my primary lens, a telephoto zoom lens such as the RF 100-400mm lens will be handling much of the balance of my needs, including complementing a 600mm lens when photographing wildlife or a 24-70mm lens when photographing landscapes.

Below are examples of what this huge focal length range looks like. These images were captured with the Canon RF 100-500mm F4.5-7.1 L IS USM Lens, availing the 500mm focal lengths for comparison.

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When mounted on an APS-C camera model, the 1.6x FOVCF sensor format will see an angle of view similar to a full-frame-mounted 160-640mm lens. This shifted-narrower angle of view range would take this lens's uses deeper into the sports and wildlife pursuits, with bird photography and big-field sports being especially good choices for this focal length range. While this range would still be useful for portrait photography on an APS-C camera, tightly-framed portraits would be most comfortable with considerable space needed for full body portraiture.

Max Aperture

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The lower the aperture number, the wider the opening, and the more light the lens can allow to reach the imaging sensor. Each "stop" in aperture change (full stop examples include f/4.0, f/5.6, f/8, f/11) increases or decreases the amount of light reaching the sensor by a factor of 2x (a substantial factor).

Seldom is a wider aperture in a lens not an advantage from an image capture capability perspective. However, if you want a lens to be smaller, lighter, and less expensive, a wide max aperture opening is usually the first aspect to be sacrificed. Decreasing the maximum aperture opening reduces the lens element diameter requirements, which enables those other desirable attributes.

With an f/5.6-8 maximum aperture opening, this lens takes the narrow aperture strategy to an extreme. Still, this is not the first Canon RF lens to utilize this concept. The RF 600mm F11 IS STM Lens and RF 800mm F11 IS STM Lens have only f/11 available. Those two lenses raised eyebrows when they were first introduced, but many photographers love the exceptional portability and low cost of these lenses. The RF 100-400 brings the same concept with the zoom range.

Want a zoom lens to be even smaller, lighter, and less expensive? Make the max aperture opening variable across the focal length range. The variable max aperture design further reduces the lens element size requirement, providing additional size, weight, and cost efficiencies while delivering the widest aperture possible at each focal length. A downside is that the widest available max aperture, f/5.6 in this case, cannot be used over the entire focal length range. Your camera will automatically account for the change in auto exposure modes, but making use of the widest-available aperture in manual exposure mode is somewhat complicated.

Narrow aperture lenses require bright light to freeze motion (direct sunlight is best) without resorting to noisy high ISO settings. When the sun goes down, action sports photographers using this lens (or similar models) will be forced to use high ISO settings to keep images bright enough while not compromising the fast shutter speeds necessary to freeze subject motion. This lens is not the right choice for indoor sports, sports under stadium lighting, or for any other use that involves quick motion in low light.

Decreasing the aperture opening provides a deeper DOF (Depth of Field) that creates a weaker, less subject-isolating background blur (at equivalent focal lengths). By virtue of its long focal lengths, this lens can still create a strong background blur at the longer focal lengths.

Here are examples illustrating the maximum blur this lens can create:

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While increased depth of field reduces the autofocus precision requirement, AF performance is reduced by the reduced amount of light reaching the imaging sensor.

How dark/slow is this lens in comparison? Here is a chart showing the max aperture breakdown in 1/3 stop increments.

Model / mm Range	f/4.5	f/5.0	f/5.6	f/6.3	f/7.1	f/8.0
Canon EF 100-400 f/4.5-5.6L IS II USM Lens	100-134	135-311	312-400
Canon RF 100-400 F5.6-8 IS USM Lens			100-122	123-155	156-258	259-400
Canon RF 100-500 F4.5-7.1 L IS USM Lens	100-150	151-253	254-362	363-471
Sigma 60-600 f/4.5-6.3 DG OS HSM Sports	60-75	76-138	139-347	348-600
Sigma 100-400 f/5-6.3 DG DN OS C Lens		100-112	113-234	235-400
Sigma 100-400 f/5-6.3 DG OS HSM C Lens		100-111	112-233	134-400
Sigma 150-600 f/5-6.3 DG DN OS Sports Lens		150-173	174-365	366-600
Sigma 150-600 f/5-6.3 DG OS HSM Sports		150-184	185-320	321-600
Sigma 150-600 f/5-6.3 DG OS HSM C		150-179	180-387	388-600
Sony FE 100-400 f/4.5-5.6 GM OSS Lens	100-115	116-161	162-400
Sony FE 200-600 f/5.6-6.3 G OSS Lens			200-299	300-600
Tamron 100-400 f/4.5-6.3 Di VC USD Lens	100-136	137-180	181-280	281-400
Tamron 150-500 f/5-6.7 Di III VC VXD Lens		150-241	242-387	383-499
Tamron 150-600 f/5-6.3 Di VC USD G2 Lens		150-212	213-427	428-600
Tamron 150-600 f/5-6.3 Di VC USD Lens		150-225	226-427	428-600

A wide range of lenses is represented in this table, but obvious is that the RF 100-400 is off the chart in comparison.

When recording video, only 1/60 second shutter speeds (twice the framerate) are typically needed (assuming you're not capturing high framerate slow-motion video), and wide apertures are not often required for 1/60 second rates in normally encountered ambient lighting.

Image Stabilization

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The longer the focal length, the larger subject details (captured at the same distance) are rendered, and the more still the camera must be held to avoid subject details crossing imaging sensor pixels, the cause of motion blur. Image stabilization is an extremely valuable feature in any lens, and it is an especially valuable feature in a telephoto lens with a narrow max aperture opening.

When the subject is not moving or not moving much, this lens's image stabilization system, rated for 5.5 stops of assistance, can make a huge difference in handheld image quality. Use this lens on an EOS R-series camera featuring In-Body Image Stabilization (IBIS), and that rating increases slightly to 6 stops. The equivalent 5.5 (or 6) stop ISO noise difference referenced by this rating is dramatic.

Testing under ideal conditions, my 100mm sharp image rate was about 80% at 1/6 second exposures. As exposures increased in duration, the percentage gradually decreased, though some sharp images were still being captured at 0.6 seconds. Holding a light lens (low inertia) with a narrow angle of view still is a challenge, and IS is especially helpful in this regard. The 400mm results were mostly sharp at 1/30 second, and many significantly longer exposures were looking good.

IS is useful for stabilizing the viewfinder, aiding in optimal composition, and handheld movie recording quality is greatly improved by IS.

Canon has been delivering outstanding image stabilization systems, and I would have been disappointed by anything less in this lens. IS makes a faint "hmmm" (even when switched off), audible only from about an inch or two from the lens. Canon's IS systems have long been well behaved, meaning that the viewfinder image does not jump during IS activation, and I do not find myself fighting against IS while recomposing or recording video. Image framing drifting while IS is active is not a problem.

This image stabilization system, as mentioned, gets a very-high 5.5-stops of assistance rating and 6 stops with IBIS. Canon has indicated that improved communications between the lens and the camera via the new RF mount make these impressive ratings possible.

This is yet another impressive high-performing Canon IS system. When you need/want to leave the tripod behind, IS will be there for you, helping to ensure sharp images and adding significant versatility to this lens.

Image Quality

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One aspect we never want to be compromised is the image quality produced by a lens. Still, those cost, weight, and size issues are in play. How does the small, light, affordable Canon RF 100-400mm F5.6-8 IS USM Lens perform optically? Let's find out.

In the center of the frame, the RF 100-400 delivers good sharpness over most of the focal length range, even with a wide-open aperture. Of course, with max apertures this narrow, there is little (or no) room to stop down before the impacts of diffraction begin to work against sharpness. Stopping down produces minor sharpness improvement with an EOS R5 behind it, except at 400mm, where the modestly soft f/8 image improves at f/11, despite the effects of diffraction beginning to show.

Often, subjects are not placed in the center of a composition. Moving farther out on the image circle, where light rays are refracted to a stronger angle than in the center, typically brings decreased sharpness, and this lens shows a gradual decline. In the mid-frame area with a wide-open aperture, 135-300mm results are still looking quite good, with 100mm results lagging slightly and 400mm results remaining similarly soft as in the center. Despite being slightly softer than the mid-frame, extreme corner performance is still good.

The resolution chart is brutal on image quality, so let's take the testing outdoors with a series of center-of-the-frame 100% resolution crop examples following. These images were captured using an ultra-high resolution (increased resolution magnifies aberrations) Canon EOS R5 with RAW files processed in Canon's Digital Photo Professional (DPP) using the Standard Picture Style with sharpness set to 1 on a 0-10 scale. Note that images from most cameras require some level of sharpening, but too-high sharpness settings are destructive to image details and hide the deficiencies of a lens.

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Be sure to find details in the plane of sharp focus for your evaluations. This discernment is most important in the longer focal length results where the depth of field is shallower.

Notice the f/8 to f/11 focus shift rearward slightly in the 300mm and especially the 400mm results?

If present, focus shift, the plane of sharp focus moving forward or backward as the aperture is narrowed (residual spherical aberration or RSA), is often made apparent in such a comparison. From 300mm and increasingly at 400mm, a slight focus shift moves the increasing depth of field primarily to the back. The details at the intended point of focus remain sharp at f/11 but slightly less so than at f/8. Much of the narrower aperture depth of field increases behind the focus subject at 100mm. This is a minor issue, but it is slightly annoying.

Next, we'll look at a comparison showing 100% extreme top-left corner crops captured and processed identically to the above center-of-the-frame images. The lens was manually focused in the corner of the frame to capture these images.

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Samples taken from the outer extreme of the image circle, full-frame corners, can be counted on to show a lens's weakest performance. While not perfect, these results are good, especially for an economical consumer-grade lens.

Does corner sharpness matter? Sometimes. Landscape photographers often desire sharp corners. Wildlife photographers, especially when blurring the background, are usually less concerned about sharp corners. Videos captured at typical wide-aspect ratios avoid the use of corners.

When used on a camera that utilizes a lens's entire image circle, peripheral shading can be expected at the widest aperture settings. At 100mm f/5.6, about 2 stops of corner shading is present. By 135mm f/6.3, the shading reduces to just over a stop. Wide-open aperture shading increases slightly at 300mm through 400mm, but the shading remains under a stop and a half. Of course, the max aperture at 400mm is f/8.

Want less peripheral shading? Stopping down is always the first step. At f/11, shading is barely 0.5 stops in the extreme corners at the wider end and just slightly more at 300mm and longer.

APS-C format cameras using lenses projecting a full-frame-sized image circle avoid most vignetting problems. In this case, the well-under one-stop of shading showing at 400mm f/8 will not be visible in most images, except perhaps those with a solid color (such as a blue sky) showing in the corners.

One-stop of shading is often used as the visibility number, though subject details provide a widely varying amount of vignetting discernibility. Vignetting is correctable during post-processing with increased noise in the brightened areas being the penalty, or it can be embraced, using the effect to draw the viewer's eye to the center of the frame. Study the pattern shown in our vignetting test tool to determine how your images will be affected. Overall, this lens's shading numbers are good.

Lateral (or transverse) CA (Chromatic Aberration) refers to the unequal magnification of all colors in the spectrum. Lateral CA shows as color fringing along lines of strong contrast running tangential (meridional, right angles to radii) with the mid and especially the periphery of the image circle showing the most significant amount as this is where the most significant difference in the magnification of wavelengths typically exists.

With the right lens profile and software, lateral CA is often easily correctable (often in the camera) by radially shifting the colors to coincide. However, it is always better to avoid this aberration in the first place.

Color misalignment can be seen in the site's image quality tool, but let's also look at a set of worst-case examples. The images below are 100% crops from the extreme top left corner of R5 frames showing diagonal black and white lines.

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Only black and white colors should appear in these images, with the additional colors indicating a presence of lateral CA in all tested focal lengths. The amount of separation is modest at the wider end. A color shift crossover (colors aligning and then reversing) happens between the 100mm and 135mm focal lengths, and the color separation becomes modestly stronger at the long end.

A relatively common lens aberration is axial (longitudinal, bokeh) CA, which causes non-coinciding focal planes of the various wavelengths of light. More simply, different colors of light are focused to different depths. Spherical aberration along with spherochromatism, or a change in the amount of spherical aberration with respect to color (looks quite similar to axial chromatic aberration but is hazier) are other common lens aberrations to observe. Axial CA remains somewhat persistent when stopping down, with the color misalignment effect increasing with defocusing. The spherical aberration color halo shows little size change as the lens is defocused, and stopping down one to two stops generally removes this aberration.

In the real world, lens defects do not exist in isolation, with spherical aberration and spherochromatism generally found, at least to some degree, along with axial CA. These combine to create a less sharp, hazy-appearing image quality at the widest apertures.

The examples below look at the defocused specular highlights' fringing colors in the foreground vs. the background. The lens has introduced any fringing color differences from the neutrally-colored subjects.

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In this test, wide-aperture lenses tend to show the most color separation, and this narrow-aperture lens shows relatively little defect in this regard.

Bright light reflecting off of lens elements' surfaces may cause flare and ghosting, resulting in reduced contrast and sometimes interesting, usually destructive visual artifacts. The shape, intensity, and position of the flare in an image are variable, dependant on the position and nature of the light source (or sources), selected aperture, shape of the aperture blades, and quantity and quality of the lens elements and their coatings. On this lens, Canon utilizes Canon SSC (Super Spectra Coating) to combat flare, and the relatively low 12-element count is additionally helpful in this regard. Putting the sun in the corner of the frame with a telephoto lens mounted is a recipe for strong flare, but this lens performs quite well.

Flare effects can be embraced or avoided, or removal can be attempted. Removal is sometimes challenging. High flare resistance is a welcomed trait of this lens.

Two lens aberrations are particularly evident in images of stars, mainly because bright points of light against a dark background make them easier to see. Coma occurs when light rays from a point of light spread out from that point instead of being refocused as a point on the sensor. Coma is absent in the center of the frame, gets worse toward the edges/corners, and generally appears as a comet-like or triangular tail of light which can be oriented either away from the center of the frame (external coma) or toward the center of the frame (internal coma). Coma clears as the aperture is narrowed. Astigmatism is seen as points of light spreading into a line, either sagittal (radiating from the center of the image) or meridional (tangential, perpendicular to sagittal). This aberration can produce stars appearing to have wings. Remember that Lateral CA is another aberration apparent in the corners.

The images below are 100% crops taken from the top-right corner of an R5 image.

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Photographing the night sky with a stationary telephoto lens and narrow aperture sounds wrong, but the stars near the north star permit exposures long enough to make some determination. The stars in these results show moderately strong stretching.

The RF 100-400 has moderate pincushion distortion that varies only modestly over the focal length range.

Most modern lenses have correction profiles available (including in-camera), and distortion can easily be removed using these. Still, geometric distortion correction requires stretching which is detrimental to image quality.

As seen earlier in the review, it is easy to illustrate the amount of blur a lens can create, and telephoto lenses are inherently advantaged in this regard. Due to the infinite number of variables present among all available scenes, assessing the bokeh quality is considerably more challenging. Here are some f/11 (for diaphragm blade interaction) examples.

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The first example set shows defocused highlights being smoothly filled, and the 9 aperture blades keep the circles nicely round (though f/11 is not stopped down significantly). The 100mm results show strong concentric circles in the periphery.

The second set of examples show full images reduced in size and looking nice.

Except for a small number of specialty lenses, the wide aperture bokeh in the frame's corner does not produce round defocused highlights, with these effects taking on a cat's eye shape due to a form of mechanical vignetting. If you look through a tube at an angle, similar to the light reaching the frame's corner, the shape is not round, and that is the shape seen here.

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As the aperture narrows, the entrance pupil size is reduced, and the mechanical vignetting absolves with the shapes becoming rounder. Most will not often want to stop this lens down significantly.

A 9-blade count diaphragm will create 18 point sunstars from point light sources captured with a narrow aperture. In general, the more a lens diaphragm is stopped down, the larger and better-shaped the sunstars tend to be. A narrow max aperture lens does not afford much stopping down before reaching apertures where diffraction causes noticeable softening of details, and these lenses typically do not produce the biggest or best-shaped sunstars. It takes a broad definition to classify this shape as a star:

The above example was captured at f/16.

The Canon RF 100-400mm F5.6-8 IS USM Lens design, as shown above, features a UD-glass element and an Aspherical element.

Overall, the Canon RF 100-400mm F5.6-8 IS USM Lens image quality is not best available, but it is quite good for price point of this lens. Those understanding the benefits the correspondingly small image quality compromise this lens avails, light weight, compact size, and low cost, should be happy with the RF 100-400.

Focusing

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The combined performance of a camera and lens's autofocus system is critical to realizing the potential image quality of the combination (unless manual focusing is in use). Impressive for a consumer-grade lens is that the RF 100-400mm F5.6-8 IS USM Lens gets Canon's high-performing Nano USM (Ultrasonic Motor) driven AF system now seen in numerous RF lenses. This lens brings a repeat of the consistently excellent performance this system delivers.

Nano USM acts like an ultra-fast version of STM AF, combining the benefits of a high-speed Ring USM actuator with an STM system stepping motor's quiet and smooth, direct, lead screw-type drive system. Like Ring USM driven AF systems, Nano USM focuses extremely fast — nearly instantly. Like STM AF systems, Nano USM focuses almost silently, with a faint clicking heard only when one's ear is next to the lens. In addition, Nano USM lenses focus smoothly, making video focus distance transitions easy on the viewer's eyes. Even the lens's aperture changes are quiet and smooth.

The Nano USM illustration below is borrowed from the RF 15-35 review.

Canon U.S.A.'s Rudy Winston states: "Canon's new Nano USM technology uses a completely different form factor, but achieves focus results within the lens via the same principles of ultrasonic vibration energy, transmitted here into linear (rather than rotational) movement within the lens. This tiny new Ultrasonic motor achieves the combination of fast, near-instant response during still image shooting, with the smoothness required for good focus during video recording."

Nano USM (and STM) lenses autofocus substantially smoother and quieter than Ring USM lenses.

Of utmost importance is AF accuracy, and from that perspective, the Canon RF 100-400mm F5.6-8 IS USM Lens performance is excellent.

An f/5.6-8 lens is not an optimal choice for photographing in low light environments, but with Canon EOS R-series cameras behind it, this lens will lock focus on contrasty subjects under moderately dim conditions.

Normal is for subjects to change size in the frame (sometimes significantly) as the focus is pulled from one extent to the other. This effect is referred to as focus breathing, a change in focal length resulting from a change in focus distance. Focus breathing has negative implications for photographers intending to use focus stacking techniques, videographers pulling focus, and anyone critically framing while adjusting focus. Modest subject magnification changes are seen in full extent focus range changes.

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Non-cinema lenses are generally not parfocal, and parfocal-like behavior is not a characteristic of the reviewed lens.

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The above examples are 100% crops focused at 400mm, with a wide-open aperture was selected for each image. Refocus after changing the focal length.

The matte-finished ribbed focus ring is nicely sized and ideally positioned in front of the zoom ring. Nano USM focusing utilizes a focus-by-wire or electrical manual focus design (vs. a direct gear-driven system). The manual focus ring electronically controls the focus of the lens.

This ring is smooth, has a nice amount of resistance, and the 1,260° of MF rotation adjusts focusing at an ideal rate for precise manual focusing, even at close distances. Need to change from a near to far focus distance? Consider using AF for the coarse adjustment as 1,260° means a lot of manual rotations (3.5). This lens features a linear focus ring. While the linear adjustment rate has advantages, turning the ring faster will not reduce the required number of rotations.

FTM (Full Time Manual) focusing is supported in AF mode with the camera in One Shot Drive Mode, but the shutter release must be half-pressed for the focus ring to become active. Note that FTM does not work if electronic manual focusing after One Shot AF is disabled in the camera's menu. The lens's switch must be in the "MF" position and the camera meter must be on/awake for conventional manual focusing to be available.

Canon continues to include AF/MF switches on the RF lenses, allowing this frequently used camera setting to be quickly changed without accessing the menu system.

With a minimum focus distance of 34.6" (880mm), the RF 100-400mm lens has an impressively high 0.41x maximum magnification spec. Very few non-macro lenses have a max magnification spec close to this one.

Model	Min Focus Distance "(mm)		Max Magnification
Canon EF 70-300mm f/4-5.6 IS II USM Lens	47.2	(1200)	0.25x
Canon EF 100-400mm f/4.5-5.6L IS II USM Lens	38.4	(975)	0.31x
Canon RF 100-400mm F5.6-8 IS USM Lens	34.6	(880)	0.41x
Canon RF 100-500mm F4.5-7.1 L IS USM Lens	35.4	(900)	0.33x
Sigma 100-400mm f/5-6.3 DG DN OS C Lens	63.0	(1600)	0.24x
Sigma 100-400mm f/5-6.3 DG OS HSM C Lens	63.0	(1600)	0.26x
Sony FE 100-400mm f/4.5-5.6 GM OSS Lens	38.6	(980)	0.35x
Tamron 70-300mm f/4.5-6.3 Di III RXD Lens	31.5	(800)	0.20x
Tamron 100-400mm f/4.5-6.3 Di VC USD Lens	59.1	(1500)	0.28x

At 100mm, a subject measuring approximately 15.9 x 10.6" (404 x 269mm) fills a full-frame imaging sensor at this lens's minimum focus distance. At 160mm, the minimum focus distance is reduced significantly to 2.7' (820mm), where a considerably smaller 6.4 x 4.3" (163 x 109mm) subject fills the frame. At 400mm, a remarkably small 3.5 x 2.3" (89 x 59mm) subject does the same.

Close-up image quality remains similar to or just slightly softer than the image quality realized at longer focus distances.

Need a shorter minimum focus distance and higher magnification? Mount an extension tube behind this lens to modestly decrease and increase those respective numbers. Extension tubes are hollow lens barrels that shift a lens farther from the camera, allowing shorter focusing distances at the expense of long-distance focusing. Electronic connections in extension tubes permit the lens and camera to communicate and otherwise function as normal. As of review time, Canon does not offer RF mount-compatible extension tubes, but third-party options are available.

Extenders / Teleconverters

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An even better option for increasing the magnification of this lens is to mount extenders (also referred to as teleconverters) behind it. The Canon RF 100-400mm F5.6-8 IS USM Lens is compatible with the Canon RF 1.4x and RF 2x Extenders. Unlike the Canon RF 100-500mm F4.5-7.1 L IS USM Lens's limited focal length range extender compatibility, the RF 100-400 can utilize extenders over the entire focal length range.

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Mounting the Canon RF 1.4x Extender behind the RF 100-400 creates a 140-560mm f/8-11 image stabilized lens that is capable of 0.12x – 0.58x maximum magnification. This focal length range will be attractive to wildlife and sports photographers, though the narrow max aperture range will be hindering to that group.

There is always some image quality reduction with an extender mounted, and the 560mm f/11 vs. 400mm f/8 shows this. This lens is least sharp at 400mm. While extenders work over the entire focal length range and may perform better at wider lengths, an extender is only advantageous to reach beyond the longest focal length natively available. Thus, performance at or near 400mm is most relevant.

The RF 100-400 has a moderate amount of lateral CA at 400mm, and I expected Lateral CA to increase slightly with the extender, impacting corner sharpness modestly. However, the change is minimal. The RF 1.4x adds a slight amount of barrel distortion that offsets some of the lens's native pincushion distortion.

AF speed is only mildly impacted when the 1.4x is mounted, with performance remaining good in even rainy outdoor conditions.

Instead of adding the RF 1.4x to the RF 100-400, consider getting the Canon RF 600mm F11 IS STM Lens. The 600 is modestly more expensive, but it has better image quality.

Mounting the Canon RF 2x Extender behind the RF 100-400 creates a 200-800mm f/11-16 image stabilized lens (capable of 0.18x – 0.83x maximum magnification). This focal length range will again be attractive to wildlife and sports photographers and especially attractive to bird photographers. The max aperture range will again not be so welcomed, sending ISO settings noisy-high in many circumstances.

The image degradation caused by the addition of a 2x extender into a lens's optical design is, as usual, strong, with contrast and resolution taking obvious hits. The softening effects of diffraction are typically strong by f/16, limiting the best possible optical performance.

If you need to get to 800mm on a budget, I recommend spending a bit more to get the Canon RF 800mm F11 IS STM Lens instead of the RF 2x. You gain a stop of aperture and get better image quality.

As with the RF 1.4x, lateral CA is not significantly increased by the RF 2x, and it adds a slight amount of barrel distortion that offsets some of the lens's native pincushion distortion.

Extenders always impact AF speed, but performance with the 2x remained usable in even dim outdoor conditions such as on a rainy day. Expect some focus hunting in low-light scenarios. Simply being able to autofocus an f/16 max aperture lens is a superpower of some of Canon's latest R-series cameras, including the R5 and R6.

While the RF 100-400mm F5.6-8 IS USM Lens provides 90% x 100% (Horizontal x Vertical) Dual Pixel CMOS AF Coverage (88% x 100% on the EOS R and RP), the addition of extenders to the optical path reduces this coverage. With Extender RF 1.4x, approximately 80% x 80% coverage is provided, and the Extender RF 2x further reduces coverage to 40% x 60%. Face+Tracking horizontal on the R5 and R6 is specified as approx. 100% x 100%.

Build Quality & Features

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Just because the lens is from the consumer lineup does not mean that attention to design details were ignored. The Canon RF 100-400mm F5.6-8 IS USM lens has an attractive design, featuring a smooth, comfortable contour and a good build quality.

Load Comparison Images

The exterior build of this lens utilizes engineering plastic for light weight and tight tolerances.

The rear-positioned, smooth-functioning zoom ring is ideally located behind the focus ring. A slight diameter increase on the zoom ring, a design feature common in the RF lens lineup, makes this ring easy to find. With the RF lenses gaining an additional ring and the rings consuming a significant percentage of the barrel, finding the right ring becomes modestly more complicated, making tactile cues such as this one helpful.

The additional ring is the knurled Control Ring, able to be configured for fast access to settings including aperture, ISO, and exposure compensation. A small amount of space is provided between the focus and control rings, aiding slightly in differentiating between the two. Note that the control ring is clicked (58 clicks per revolution) by default, and this ring's clicks are audible in camera-based audio recordings. Canon offers a click stop removal service for this ring (at a cost).

As illustrated in some of the product images in this review, the RF 100-400 lens extends modestly (2.99", 76mm) when zoomed to the long end. The extended inner lens barrel has little play. An extension lock switch is provided and was not needed for the review lens.

The AF/MF and IS switches are flush-mounted and low-profile, with just enough raised surface area available for easy use, even with gloves. These switches snap crisply into place. Interesting but normal for RF lenses is that changing the AF/MF switch position opens the lens aperture momentarily when the camera is powered off.

No dust or other sealing has been claimed for this lens model. Use a camera rain cover if such conditions are possible.

There was no mention of fluorine coatings.. Fluorine coatings are commonly used on the front and rear lens elements to avoid adhesion of dust and liquids and to make cleaning easier.

This lens's small size and light weight are huge advantages it holds. Those spending long amounts of time with this lens in hand or carried in a case will love these features. Check out these comparisons.

Model	Weight oz(g)		Dimensions w/o Hood "(mm)		Filter	Year
Canon EF 70-300mm f/4-5.6 IS II USM Lens	25.1	(710)	3.1 x 5.7	(80.0 x 145.5)	67	2016
Canon EF 100-400mm f/4.5-5.6L IS II USM Lens	56.1	(1590)	3.7 x 7.6	(94.0 x 193.0)	77	2014
Canon RF 100-400mm F5.6-8 IS USM Lens	22.4	(635)	3.1 x 6.5	(79.5 x 164.7)	67	2021
Canon RF 100-500mm F4.5-7.1 L IS USM Lens	48.2	(1365)	3.7 x 8.2	(93.8 x 207.6)	77	2020
Sigma 100-400mm f/5-6.3 DG DN OS C Lens	40.9	(1160)	3.4 x 7.8	(86.0 x 197.2)	67	2020
Sigma 100-400mm f/5-6.3 DG OS HSM C Lens	40.9	(1160)	3.4 x 7.2	(86.4 x 182.3)	67	2017
Sony FE 100-400mm f/4.5-5.6 GM OSS Lens	49.2	(1395)	3.7 x 8.1	(93.9 x 205.0)	77	2017
Tamron 70-300mm f/4.5-6.3 Di III RXD Lens	19.2	(545)	3.0 x 5.8	(77.0 x 148.0)	67	2020
Tamron 100-400mm f/4.5-6.3 Di VC USD Lens	40.1	(1135)	3.4 x 7.8	(86.2 x 199)	67	2017

For many more comparisons, review the complete Canon RF 100-400mm F5.6-8 IS USM Lens Specifications using the site's lens specifications tool.

Here is a visual comparison:

Positioned above from left to right are the following lenses:

Canon EF 70-300mm f/4-5.6 IS II USM Lens
Canon RF 100-400mm F5.6-8 IS USM Lens
Canon EF 100-400mm f/4.5-5.6L IS II USM Lens
Canon RF 100-500mm F4.5-7.1 L IS USM Lens

The same lenses are shown below with their hoods in place.

Use the site's product image comparison tool to visually compare the Canon RF 100-400mm F5.6-8 IS USM Lens to other lenses. I'll preload another comparison in that link.

Also relatively compact are the 67mm filters this lens is compatible with. The 67mm size is relatively affordable and common, making effects filter sharing easier.

The RF 100-400 is Canon's first 100-400mm lens to ship without a tripod ring, and no tripod ring is optionally available. The size and weight of this lens simply do not warrant the need for that accessory.

Canon continues to omit lens hoods from their consumer-grade lens boxes. The large molded plastic Canon ET-74B Lens Hood is optional, and this seemingly low-cost accessory has a high price. Still, I advise getting and using the hood most of the time. I sometimes remove lens hoods when shooting in strong wind (to reduce the size footprint), but I seldom go sans hood otherwise.

In addition to blocking contrast-robbing and flare-inducing light, the RF 100-400's hood protruding in front of the lens naturally helps keep dust, water, fingers, limbs, etc. off of the glass. Lens hoods absorb some impact, providing physical protection to the camera and lens from bumps. This hood's round shape permits standing the lens on end (if deemed safe), though this shape lacks the easier installation alignment of a petal design.

The drawstring Canon LP-1224 Lens Case (pouch) is also optional. Consider a Lowepro Lens Case or Think Tank Photo Lens Case Duo for a quality, affordable single-lens storage, transport, and carry solution.

Price, Value, Compatibility

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While this is a consumer-grade lens, the price is still quite low for a Canon RF lens. Those on a budget will likely find the Canon RF 100-400mm F5.6-8 IS USM Lens to provide a lot of benefit for the cost.

As an "RF" lens, the Canon RF 100-400mm F5.6-8 IS USM Lens is compatible with all Canon EOS R-series cameras. Canon USA provides a 1-year limited warranty.

The reviewed Canon RF 100-400mm F5.6-8 IS USM Lens was online-retail sourced.

Alternatives

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At review time, Canon has only one other RF zoom lens that reaches beyond 240mm. The awesome Canon RF 100-500mm F4.5-7.1 L IS USM Lens is in a different class, but let's make the comparison.

It seemed hard to imagine the consumer lens could equal or best the image quality of one of the sharpest professional L-series models ever produced, and the image quality comparison confirms the expectation. The RF 100-500 is sharper (better contrast and resolution) wide open than the RF 100-400 gets at any aperture. At equal apertures, the RF 100-500 has less peripheral shading, and it has slightly less geometric distortion as well.

The Canon RF 100-400mm F5.6-8 IS USM Lens vs. Canon RF 100-500mm F4.5-7.1 L IS USM Lens comparison shows obvious strong differences. Smaller size and lighter weight are two major advantages the RF 100-400 holds. The smaller size means smaller filters for the RF 100-400, 67mm vs. 77mm. The RF 100-400 has a higher maximum magnification (0.41x vs. 0.33x) and a .5-stop higher image stabilization rating (5.5 vs. 5), though both lenses are rated to 6 stops with coordinated IBIS. The RF 100-500 has a considerably longer focal length range, has a zoom torque ring, has a focus distance limit switch, and features three IS modes. As mentioned at the beginning of the review, the RF 100-500 costs more than 4x as much, a factor that will outweigh all others for some budgets.

The latest-released EF telephoto zoom lens most similar to the RF 100-400 is the Canon EF 70-300mm f/4-5.6 IS II USM Lens.

In this case, I expected the two lenses to show similar (good) optical quality. The image quality comparison shows that expectation realized, with the RF 100-400 perhaps being slightly sharper. The EF 70-300 has less peripheral shading at equivalent settings. The RF 100-400 has less geometric distortion in the wider shared focal lengths, and the EF 70-300 has a slight advantage at the long end.

The Canon RF 100-400mm F5.6-8 IS USM Lens vs. Canon EF 70-300mm f/4-5.6 IS II USM Lens comparison shows the RF 100-400 modestly lighter and slightly longer. The RF 100-400's focal length range is shifted to longer numbers. Those photographing sports and wildlife will usually prefer the 100-400mm range, while those concentrating on portraiture will typically prefer having the 70-99mm range included vs. 301-400mm. The RF 100-400 has a higher maximum magnification (0.41x vs. 0.25x) and a considerably higher image stabilization rating (5.5 vs. 4), while the EF 70-300 has an LCD panel. The 70-300 has a moderately lower price tag, but the mount adapter required to use the EF lens on Canon EOS R-series cameras adds to that lens's cost, size, and weight considerations.

How does the Canon RF 100-400mm F5.6-8 IS USM Lens compare to the Sigma 100-400mm f/5-6.3 DG OS HSM Contemporary Lens? This Sigma lens is a great value. It is a lens I've frequently recommended for those wanting a lightweight, long focal length telephoto zoom lens.

The image quality comparison at 100mm equalized at f/5.6, the Sigma lens is a bit sharper in the mid-frame and periphery, though it produces more lateral CA. The Sigma's sharpenss advantage is slightly reduced at 135mm and harder to detect at 200-300mm, though the Canon lens has more lateral CA at these focal lengths. At 400mm, the Canon lens sharpness degrades somewhat, and the Sigma lens has the clear advantage at this focal length. The longest focal length is where extenders/teleconverters provide the biggest advantage, and the Sigma lens performs considerably better at 560mm and 800mm.

The Sigma lens's 1/3 - 2/3 stop wider aperture advantage is an image quality factor. At equal apertures, the Sigma lens has less peripheral shading but shows more flare effects, thanks in part to a 21 lens element optical formula vs. 12 for the Canon lens. The Sigma lens produces less geometric distortion over the wider half of the zoom range.

The Canon RF 100-400mm F5.6-8 IS USM Lens vs. Sigma 100-400mm f/5-6.3 DG OS HSM Contemporary Lens comparison shows the Sigma lens having larger dimensions and considerably heavier (approaching 2x heavier) weight. The Sigma lens features a focus distance limit switch. The Canon lens has a higher maximum magnification, 0.41x vs 0.26x. The Sigma lens is priced nearly 50% higher than the Canon RF 100-400, and the mount adapter required to use the Sigma lens on Canon EOS R-series cameras adds to the Sigma lens's cost, size, and weight considerations.

How does the Canon RF 100-400mm F5.6-8 IS USM Lens compare to the Tamron 100-400mm f/4.5-6.3 Di VC USD Lens?

The image quality comparison shows the two lenses with equalized apertures performing similarly over most of the range. The Tamron lens is slightly sharper at 400mm and with extenders/teleconverters, and it has less lateral CA over the longer half of the range. The Tamron lens's mostly 2/3 stop wider aperture advantage is an image quality factor. The Tamron lens has less peripheral shading at the long end, has less geometric distortion except at 400mm, and with 17 lens elements vs. 12, shows more flare effects.

The Canon RF 100-400mm F5.6-8 IS USM Lens vs. Tamron 100-400mm f/4.5-6.3 Di VC USD Lens comparison shows the Tamron lens larger and considerably heavier. The Tamron lens features a focus distance limit switch. The Canon lens has a higher maximum magnification, 0.41x vs 0.28x, and a higher image stabilization system rating, 5.5 stops vs. 4, that offsets the maximum aperture advantage with a motionless subject. The Tamron lens has a modestly higher price, and the mount adapter required to use this lens on Canon EOS R-series cameras adds to the Tamron lens's cost, size, and weight considerations.

Use the site's comparison tools to create additional comparisons.

Summary

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For those not requiring the widest aperture or professional build quality and features, for those not interested in carrying the size and weight professional features require, for those not requiring the ultimate image quality, and for those not able to afford a pro-grade price, the Canon RF 100-400mm F5.6-8 IS USM Lens quickly becomes an obvious choice. The RF 100-400 is a comfortable to carry (compact and lightweight), affordable telephoto zoom lens destined to capture a huge number of family memories, landscape masterpieces, and exciting wildlife portraits.