Canon RF 600mm F4 L IS USM Lens Review

Let me introduce you to Canon's ultimate wildlife and big field sports lens, the RF 600mm f/4L IS USM.

I'll start with a brief introduction to this model before diving into the full review. The first important piece of information to share is that the Canon RF 600mm F4 L IS USM Lens, with a brushed metal EF to RF mount adapter built in (and the focus distance window removed), is essentially the same as the Canon EF 600mm f/4L IS III USM Lens with a Mount Adapter EF-EOS R behind it and a new wiring system in it. This includes optical and mechanical performance.

It is easy to say that Canon took the easy option when creating the 600mm f/4 for the RF mount, and it is also hard to argue against that statement. However, it is unlikely that today's optical advances were significant enough to justify a new design since the EF lens introduction less than three years earlier. Also notable is that long focal length lenses tend to benefit less from the short flange distance enabled by the mirrorless camera models, reducing the justification for a redesign.

Why bother developing the RF model if the mount is the only significant design improvement, and compatibility with EOS DSLR Cameras is foregone? Eliminating the mount adapter creates a slightly tighter, more secure fit and reduces the weight (very little) for two minor benefits. That the adapter is no longer at risk of being forgotten or lost is a benefit.

An interesting benefit provided by the technology in the RF mount (specifically) is a CIPA image stabilization assistance rating increase to 5.5 stops from 5.0 stops.

A significant benefit of the built-in RF mount is compatibility with the Canon RF 1.4x and RF 2x Extenders, compatibility that the Canon mount adapter (probably) should have availed.

I opted to replace my EF 600mm lens with the RF version. However, as discussed, the RF lens is practically the same as the EF lens, and much of this review will be the same (including many of the sample pictures).

If you can get past the price, the RF 600mm F4 L IS Lens will blow you away in most other regards. This lens is one of the most incredible lenses available and the ultimate big field action sports lens. The RF 600 f/4 IS features an impressive design, superb image quality, incredibly fast AF, and best-available build quality.

The RF 600mm f4 L IS USM Lens is the 7th generation in Canon's 600mm f/4 series, slotting alongside the 6th generation Canon EF 600mm f/4L IS III USM Lens. The RF 600 F4 is the 4th IS version of this lens model.

Owners of this lens will, like owners of the previous lens versions, primarily be professional and serious amateur photographers (or simply wealthy). Due to this lens's focal length and max aperture, it will mainly be used for sports, wildlife, and photojournalistic pursuits.

Here is a brief history based primarily on the EF version III lens relative to the previous generation of this lens:

This EF version III lens's predecessor was phenomenal in all respects, a new version had to show a significant advantage, and it was hard to believe that better was achievable.

While at first glance, the Canon EF 600mm f/4L IS III USM Lens looks like the II, the appearance seems more accidental than intentional as the III is a completely new lens design, with the most apparent difference being dramatically lighter weight. Photographers have many opinions about what they want in a lens, but universal for this one lighter weight. With the version II lens dropping 3.2 lbs (1,440g), it was hard to imagine a significant additional weight loss delivered only seven years later. However, the version III lens saw significant additional weight loss.

Let's put the Canon super-telephoto weight loss program into a chart:

Model	Weight		Year
Canon RF 600mm F4 L IS USM Lens	6.81	(3090)	2021
Canon EF 600mm f/4L IS III USM Lens	6.72	(3050)	2018
Canon EF 600mm f/4.0L IS II USM Lens	8.65	(3920)	2011
Canon EF 600mm f/4.0L IS USM Lens	11.83	(5360)	1999

The RF 600mm F4 L IS USM weighs only approx. 6.8 lbs (3,090g). That is approximately 1.8 lbs (830g) less than the version II lens (21% less) and an incredible 5.0 lbs (2,270g) less than the version I lens (58% less).

Upon the curtain going up at the announcement event for this EF version III lens (Elliot Peck, Canon USA Senior VP & GM shown above), I held both versions of the 600 simultaneously. I was blown away by the difference that felt more significant than the numbers show, and part of the reason for the lighter feel was that the weight had been shifted rearward, giving the lens a better balance.

So, how were the weight savings and improved balance created?

The Canon-supplied graphics below show the design of the last three Canon EF 400mm f/2.8 image-stabilized lenses. The 600mm design graphics were not available. However, aside from being somewhat longer, the 600mm designs mirror the 400mm designs for each respective generation of lens, meaning that this 400mm design history illustration is representative of the 600mm lenses also. Light green represents UD elements, violet indicates a fluorite element, and the dark green elements are Super UD.

Notice that the protective meniscus front lens element in the I series lens disappeared in the II, with a less-expensive-than-UD next-in-line element becoming frontmost. Additional weight reduction was found in the utilization of fluorite elements.

The III's biggest design secret is moving all but one of the large front set of lens elements considerably far rearward, where they also become smaller. As mentioned, this design also moved the center of gravity rearward for better comfort and handling. The front of the lens gets moved the most, and it is now considerably lighter, though with decreased momentum, the new lens is not as easy to hold stationary.

The addition of the Super UD element was part of the design change. Check out that awesome 3rd lens element, a thin concave optic tightly nested between the two fluorite elements. Per Canon, "This lens element is so delicate that simply holding the edges of it in your hand can cause localized warping due to body heat."

Interestingly, the EF 600 III lens and EF 400 f/2.8L IS III were the first Canon lens designs featuring new glass materials. "This glass has a comparatively higher refractive index than general low-dispersion glass, and has a low specific gravity. By using the new glass material in the first, large-diameter lens element [which cannot be reduced in size due to the focal length and max aperture requirements], the weight is reduced and spherical and chromatic aberration are suppressed." [Canon]

Another interesting design element is the forward-positioned aperture, resulting in the largest EMD (electromagnetic diaphragm) in an EF lens or RF lens to date and representing another design challenge Canon has overcome.

Focal Length

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While this lens is impressive in many ways, it is the 600mm super-telephoto focal length you should interest you most. That said, despite the size and cost of this lens, it provides an angle of view similar to all of the other (accurately-denoted) 600mm lenses (including zoom lens options). What is the 600mm focal length's narrow angle of view commonly used for?

When you need to frame a subject tightly and can't get closer, due to:

• Physical barriers (streams, cliffs, etc.)
• Legislated barriers (lines on a field, property boundaries, etc.)
• A subject that does not tolerate closer photographers (skittish birds, for example)
• Safety reasons (dangerous wildlife, high-speed vehicles, etc.)
• Stealth requirements (law enforcement mission, for example)
• Becoming a viewing obstruction (such as getting in front of spectators at a speaking event at a large venue)
• Laziness (sometimes relaxing is a joy of photography)

Then, you might need a 600mm lens.

If you simply don't want to get closer, including for comfort reasons or to avoid impacting wildlife behavior, a 600mm lens might be just right. Sit in the comfort of your car, avoid crossing a creek, stay back from the surf, stay out of view, etc.

When you want to capture a compressed look from a distant perspective, you might want a 600mm lens. When you want to create an extremely strong background blur, isolating a subject from even a busy and otherwise-distracting background, a 600mm lens might be precisely what you need, especially a 600mm lens with an f/4 max aperture.

While a 600mm lens has a wide variety of uses, wildlife and sports are at the top of its most frequently used-for list, with most other 600mm uses occurring at a far lower frequency. When using a camera with a full-frame imaging sensor, a 600mm f/4 lens has long been my first choice for wildlife photography. Subjects ranging from small birds up to large game are readily captured with this focal length. Wildlife is typically most active early and late in the day when the light is dim, and the f/4 aperture (more about this feature soon) is a great complement to the narrow angle of view.

This lens's light weight and long focal length makes it a good choice even for handheld birds-in-flight and flying aircraft such as at airshows.

When using a camera with a full-frame imaging sensor, a 600mm lens has long been my first choice for field sports photography, including soccer and some running events. This lens is an excellent choice for baseball, football, and a host of other sports. Watch for this lens in high numbers at the Olympics, the Super Bowl, the World Cup, and many other major sporting events.

Photojournalists and others covering events will love the 600mm reach. When photographers covering events are not permitted close access to their subjects, including concerts, speaking events, etc., this focal length will often provide the reach needed.

The 600mm focal length used on smaller APS-C/1.6x (FOVCF) imaging sensor format cameras (none are available with an RF mount as I write this) provides a narrow angle of view, equivalent to a 960mm lens on a full-frame camera. This considerably narrower angle of view diminishes the scenarios this lens is ideally suited for, though I rarely hear a bird photographer complaining about having too much focal length. The 960mm equivalent angle of view is challenging to use at many sports events (keeping a subject in the frame is challenging), and it is even too long for some wildlife photography. Moving back can be an answer, but obstacles can enter the sight path, and a longer distance permits heatwaves to become a more significant issue.

While on the heatwaves topic, just because you have an amazing 600mm lens doesn't mean that you can create sharp images with it, even when using the fastest shutter speeds and the best techniques.

When present, heat shimmer/haze/waves create optical distortion that will diminish the quality of long-distance photos, a problem I encounter frequently. My first use of the 600 L IS III lens was at a soccer tournament held at an impressive venue featuring artificial turf fields. While the sunny weather made this spring event remarkably comfortable to watch, the sun shining on artificial turf spells doom for image quality. Looking across the field, I could see the white field lines dancing in the heatwaves. I knew that my images would all be compromised, and they were, including the sports sample image shared above (see the strange background blur?). This scenario would have been better covered with a 400mm lens that would have delivered better (roughly 1/3 better) image quality when subjects were ideally-framed (closer required at 400mm). There would have been less turbulent air within the shorter subject distances.

When reviewing long prime telephoto lenses, I like to discuss the optimal framing distance range. Image cropping is often required during post-processing when a prime (non-zoom) lens is used to capture the action from a fixed position, as is frequently the case with sports photography. A longer focal length lens has a narrower angle of view, which requires you to be farther from the subject for optimal framing. One huge advantage that a narrower angle of view provides is a deeper optimal framing distance that provides a longer duration to capture an optimally-framed subject. That advantage can result in less cropping needed with higher resolution retained.

Explaining that concept, if you photograph a running person with a 24mm lens on a full-frame format DSLR, the optimal framing distance to capture the entire person might be 9' (3m). At 18' (6m), that person would only be 1/2 of the optimal size in the frame. A person running at full speed will only momentarily be near that optimal distance.

In contrast, a 600mm lens would frame this person similarly optimally at around 225' (69m), with the 1/2 optimal distance being 450' (138m). It takes a running person far more time to cover this 250' (69m) 1/2 to optimal distance than the 24mm lens's 9' (3m) distance. Distances much closer than optimal will often result in the subject being cropped in the frame with both focal lengths being compared, so I'll not count this distance (but the rate of cropping increase is dramatically slower with the 600). The longer the subject remains at the near-optimal framing distance, the more time you have to capture ideally framed shots. Also, the longer focal length allows a much greater area of an event to be covered from a single position.

This explanation does not say that a 600mm lens is always a better choice, but it is the correct answer for many sports events. There are longer focal length lenses available (such as Canon's EF 800mm f/5.6L), and these lenses provide even more significant areas of optimal coverage. However, these longer lenses do not offer the big f/4 aperture advantage, and the narrow 800mm angle of view challenges fast-moving subject framing and may be too narrow for the subject.

Here is a full-frame example of the 300-600mm focal length range captured by a zoom lens (the 600mm sample shown here might be a slightly wider angle than true a 600mm view):

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Want to add some color to your portfolio? Just direct this lens at an even modestly colorful sky just after sunset or before sunrise (never look at the sun through a long telephoto lens unless an adequate solar filter is properly installed).

I wouldn't buy this lens specifically for photographing landscapes, but if you have the lens, landscapes, flowers, and many other subjects can be captured with differentiatingly great results. Photographing the sun (with a safe solar filter) and moon are uses that might be worth buying this lens for.

The solar eclipse sample above was captured with the EF version II lens with a 2x extender mounted behind it.

Max Aperture

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The Canon RF 600 F4 L IS lens has the longest focal length available in a lens with an f/4 max aperture. While f/4 is not an especially wide aperture rating for lenses in general, aperture is measured as a ratio of lens opening to focal length. At 600mm, an f/4 aperture is massive, and this huge opening is the primary reason for the large size, heavy weight (relative to most lenses), and high cost of this lens. That aperture is also the key to this lens's awesomeness.

There are other 600mm lenses available, and some of those have a zoom focal length range advantage. However, none of the zoom lens options have an aperture wider than f/5.6. That one stop (or more) difference is huge, enough to make the difference between getting a great shot with a strong background blur and getting a blurry or noisy image with more background in focus.

When you want to stop action, including sports action and wildlife in motion, especially in low light, when wildlife is most often active and when sports are often played, you want the f/4 feature in your 600mm lens.

When you want to isolate the subject from even a busy, distracting background, you want f/4. At f/4, the 600mm focal length creates a shallow depth of field that combines with the strong 600mm super-telephoto magnification to deliver the strongest background blurs available in any lens (at equivalent focus distances or subject framing). Most of the common uses for this lens do not permit manipulation of the background, and the backgrounds found in many of the venues this lens gets used in tend to be busy and distracting. Use this lens to blur the distractions away, turning advertisement banners, fans, and their clothing, apparatus, gear, seating, etc., into blurs of color, making the subject stand out, popping from the frame. Look at the images in popular sports magazines and websites to see the results this lens can produce.

The f/4 aperture at 600mm can markedly differentiate your work from the crowd. When using this lens (or its predecessors), I use f/4 far more than any other setting, and I would be satisfied if only f/4 was available.

Despite the f/4 aperture being so huge in a 600mm lens, it may still not be adequate for photographing sports under average sports field lighting at night or indoors. An f/2.8 aperture may prove the minimum aperture desired in these dark venues, and the Canon RF 400mm F2.8 L IS USM Lens or Canon EF 400mm f/2.8L IS III USM Lens may be the better choice for those environments.

The other important camera feature that works better with a large amount of light as provided by this lens's aperture is the AF system. Subjects for 600mm lenses are often in motion, and the increased AF performance can be a key to in-focus images.

Here is a look at a range of 600 f/4 apertures as seen by the EF version II lens:

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The widest apertures create a great background blur, while the narrower apertures keep more of this close young whitetail deer in focus.

Canon currently provides a wildlife-friendly EF 800mm lens option with a 1-stop-narrower max aperture, but the 600 f/4L exceeds that focal length at the same aperture with a 1.4x extender mounted behind it.

Image Stabilization

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Practically everything in the EF III lens was new, including the image stabilization system that has achieved an impressive up to 5-stop CIPA rating. The RF lens gets a slightly higher 5.5 stop rating, with the increase directly attributed to the RF mount. Note that this lens does not support coordinated IS, but IBIS is said to still provide some benefits.

The RF and version III lenses are far lighter than the previous generation lenses, but these are still not light lenses to handhold. Handholding the III completely unsupported (no help from an elbow resting against the body) for the many hundreds of images required for a complete image stabilization test session was a big workout. To help ensure that fatigue didn't interfere with the results, I opted to test the narrowed-down sharp and nearly-sharp shutter speed range twice. I learned that, under ideal conditions, my keeper rate was rather solid at 1/20 second exposures and still high (about 75%) with 1/13 second exposures. Sporadic sharp images could be made at even longer exposures.

Keep in mind that this EF version III lens testing was done on an ultra-high resolution Canon EOS 5Ds R. Higher imaging sensor pixel density makes motion blur more-readily-noticeable than lower resolution models as details cross over pixels with less movement. Basically, motion is being magnified by the tighter spacing of pixel wells.

As with many of Canon's L-series telephoto lenses, Three IS modes are provided. Mode 1 (general-purpose), Mode 2 IS (for panning with a subject, one axis of stabilization is provided), and Mode 3. Mode 3 is useful for tracking erratic action. In this mode, image stabilization is active and ready for use the moment the shutter releases, but actual stabilization is not in effect until that precise time. The view seen through the viewfinder is not stabilized, allowing erratic subject motion to be tracked without fighting against image stabilization trying to stabilize the view. IS Mode 3 is designed to detect panning motion, and when detected, the lens will only apply Image Stabilization at right angles to the direction of the detected movement (like IS Mode 2). The latest word I've heard from Canon is that mode 1 can optimally be used for nearly all situations, including while using a tripod or monopod and while photographing action.

A noticeable click is heard when IS starts and again when it stops, but only quiet whirring and clicking are audible while IS is active. This IS implementation is exceptionally well behaved – the image in the viewfinder does not jump around when the system activates, and the image does not drift while IS is active. IS aids greatly in establishing ideal subject framing, and I had no problem tracking action in Mode 1.

Canon's super-telephoto lenses have a secondary IS mode that automatically senses a tripod in use, then attempting to eliminate shutter shock, wind vibration, and other sources of remaining movement.

While stopping camera motion-induced image blur is image stabilization's primary job, it has another significant benefit, aiding in AF precision. The camera's AF system can produce better focus precision if the image it sees is stabilized. Canon contends that this is true even with a subject that is in motion, and the 600mm f/4 combination producing a potentially shallow depth of field makes AF precision especially critical.

The RF and EF version III lenses can be handheld for significant periods, and the image stabilization system in these lenses greatly extends their versatility in that regard.

Image Quality

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We're reviewing another big white Canon super-telephoto lens, so it is time to dig out all of those big superlatives to describe the image quality. With the version II lens delivering incredible image quality, there was little room for improvement with the III, and few would have accepted any decline in image quality despite the weight reduction. The RF lens has the same optics as the EF III lens, and many of the examples below are from the EF III lens.

The f/4 aperture is critically important to this lens, as wildlife (and often sports) is most often photographed early and late in the day (low light levels), and action is often involved. High ISO settings are often needed to stop this action even at f/4, and with smaller, lighter lens options available with a narrower max aperture available, stopping down should only be needed to gain depth of field. Thus, the wide-open image quality is what matters most.

With a wide-open f/4 aperture, this lens is razor sharp across the entire full-frame image circle. Little benefit is seen by stopping the aperture down.

Our lab sharpness tests tell the story best, but I attempted to create some outdoor comparison examples to share. To eliminate variations, outdoor testing requires the stable lighting of a clear sky, and heatwaves are often present when the sky is clear. When magnified with a 600mm lens, heatwaves prevent representative results. Wind, even light wind, can impact the image quality realized by a large lens such as this, with the narrower angle of view magnifying any vibration.

With these caveats in mind, here are a series of center-of-the-frame 100% resolution crop examples. These images were captured using an ultra-high-resolution Canon EOS 5Ds R with RAW files processed in Canon's Digital Photo Professional using the Standard Picture Style and sharpness set to only "1" (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 the center of the sharp focus plane in these images (not all details should be sharp). Note that the fawn's eye crop image has some noise reduction added. Also, remember that the sharpness setting could be turned up slightly.

Focus shift, the sharp focus plane moving forward or backward as the aperture is narrowed (residual spherical aberration), is not an issue with this lens.

Here is a quick look at corner performance.

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I have used the EF 600 L IS III lens extensively in the field and am pleased with the results.

I generally don't like vignetting, but I don't mind having some vignetting from lenses such as this one. Sports action and wildlife shots seldom have a primary subject (or a primary subject's face) in the corner of the frame, and the vignetting-darkened borders can draw the viewer's attention to the subject and their face. At f/4, this lens has just a touch of this effect. The about-1.4-stops of corner shading is mild and usually only slightly noticeable. If you cannot have any shading in your image corners, the about-0.5-stops of shading in f/5.6 corners will likely make you happy, and practically no shading is present at narrower apertures.

APS-C format camera owners will seldom notice the about-0.6-stops of shading at f/4.

Lateral (or transverse) CA (Chromatic Aberration) refers to colors of the spectrum being magnified differently. 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 easily be seen in the site's image quality tool, but let's also look at a worst-case example. The image below is a 100% crop from the extreme top left corner of an ultra-high-resolution EOS 5Ds R frame showing diagonal black and white lines.

There should be only black and white colors in this image, which is essentially what we see here. This lens shows a minor amount of lateral CA.

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.

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The silver jewelry in the 100% crops above shows a slight color difference in the foreground vs. background, and the details in the center of depth of field are sharp, reflecting strong performance.

Canon optical technologies deployed on this lens include Super Spectra Coating (SSC), rejecting extraneous light wavelengths, and Air Sphere Coating (ASC, a thin film containing silicon dioxide and air formed on top of traditional multi-coating), helping to minimize glare and reflections. Additionally, the new optical design, moving the second lens element toward the rear of the lens, with only one large element remaining in the front, aids in reducing flare and ghosting. Our standard flare test involves placing the sun in the corner of the frame. While this test works excellently with wide angles through short telephoto focal lengths, longer focal lengths such as this always show a lot of flare from this test. Because I don't like seeing smoke come out of the camera, 600mm lenses do not participate in our standard flare testing.

This lens is about as linear-distortion-free as lenses get. It is unlikely that you will feel the need to distortion-correct a Canon RF 600mm F4 L IS Lens image.

Very obvious is that this lens can create a crazy-strong background blur, and the quality of that blur is good. Here are bokeh samples:

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The f/8 examples show performance that is normal, and the "Cat's Eye" example, shows the top corner from the rightmost 1/3 of the frame where defocused highlights become squeezed at f/4.

How good is the optical quality of the Canon EF 600mm f/4L IS III USM, and by inheritance, the RF 600mm F4 L IS USM Lens? Overall, it is remarkably good. That the version II lens was already so impressively sharp is really the only negative attribute I had for the version III lens.

Focusing

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Critical for the success of a lens with a shallow depth of field used primarily to photograph fast action is its AF performance. Canon's super-telephoto lenses have long delivered the best-available autofocus performance, and this lens continues that trend.

As you would expect, this lens gets all of the latest available upgrades — identical to the EF III. "Mechanically-related AF improvements include reduced drive load, thanks to glass materials in the focus lens group that are nearly one-fifth the previous weight." [Canon] Also included is the latest microprocessor for improved calculation speed. Canon claims a faster minimum focus distance to infinity focus time, despite a shortened minimum focus distance, than with the version II lens. That lens focused fast, so don't expect to find the difference dramatic, but this is a fast-focusing lens.

In addition to being fast and accurate, this lens's internal AF system is quiet. Some quiet internal shuffling along with quiet clicks can be heard if you listen carefully, but I don't notice the sounds when shooting.

This super-telephoto lens includes a Focus Preset feature. Set the Focus Preset to a specific distance. When your shooting needs require that particular distance, turn the white spring-loaded playback ring located in front of the focus ring, and the lens will automatically adjust to the preset distance. New with the EF version III lens was a direction-sensitive feature that permits a different distance to be set for each rotation direction. The Focus Preset switch settings include OFF, ON, and an ON with audible focus confirmation. Use this feature to quickly adjust focus to a known distance or to an approximate distance where fine-tuning can quickly attain proper focus.

A 3-position focus limiter switch allows focusing distances to be limited to a subset of this lens's focus distance range. In addition to the full range, restricted limits of 13.8' — 52.5' (4.2m — 16m) and 52.5' (16m) — ∞ are selectable for improved focus lock times and reduced focus hunting when photographing subjects remaining within these ranges.

Four autofocus stop buttons in the black ring near the objective lens allow autofocus to be temporarily stopped. I use AI-Servo (continuous) focusing mode for shooting sports but sometimes shoot focus-and-recompose images such as portraits during the event. The autofocus stop feature makes it easy to obtain focus lock, turn off autofocus, and recompose with framing that places the active focus point(s) off of the subject, including in the periphery of the frame. Another excellent use for this feature is when an image has been captured with suboptimal framing. Simply press a focus stop button and then capture enough images to be stitched together during post-processing. Of course, switching the lens to manual focus mode has the same effect.

New on the 2010-announced super-telephoto lenses was a third focusing mode. In addition to AF and MF, a "PF" or Power Focusing mode was included, and this mode has returned with the RF and series III lenses. When first introducing this feature, Canon USA said the feature helped "...moviemakers achieve smoother and more appealing focus shifts when filming."

Turn the focus preset playback ring (very) slightly to get low-speed electronically-driven AF, and turn it to a greater degree to obtain a higher rate with the direction of ring rotation determining the direction of focus distance change. The feature works nicely, but you will need a solid tripod setup and a steady hand not to induce movement while turning the ring. The power focusing is extremely quiet. Note that AF does not work in PF mode, though manual focusing is available in this mode.

Those interested in manually focusing this lens have definitely not been forgotten, and this lens's focus ring lens provides a superb manual focus experience. Instead of a conventional mechanically-linked manual focus drive, Canon implemented electronic manual focusing starting with the EF III lens. This decision simplified the overall design, saving weight and increasing expected reliability — and seemingly prepping for the R-series technology.

The RF 600mm F4 L IS lens's manual focus ring is ideally located, is large, has a sharply-ribbed rubber surface with a great feel and ideal rotational resistance, and is smooth with no play. With an ear against the lens, a series of tightly-spaced click sounds can be heard while manually focusing.

A feature commonly implemented on electronic focusing lenses is variable speed drive rate dependent on the focus ring rotational speed. Unfortunately, this feature is often not optimally implemented, and fortunately, Canon has a better option for this lens. Via a switch, this lens offers three linear drive speeds. Mode 1 adjusts the focus more slowly than on the II series, and precisely focusing is challenging in this mode. Mode 2 and 3 become respectively slower, enabling fine control of the focus distance. You don't want to use the 3 setting to chase sports action, but this mode allows for precise manual focusing.

FTM (Full Time Manual) focusing is supported in AF mode while in One Shot Drive Mode, but the shutter release must be half-pressed for the focus ring to be enabled. I often manually adjust the focus distance to track action while I'm not actively shooting, such as to watch sports action at the other end of the field or to pre-focus on where I expect the action to be next. AF is now required for this when shooting in AI Servo mode. Note that FTM does not work if electronic manual focusing is disabled in the camera's menu (if this option is present). The lens's switch must be in the "MF" position and the camera meter must be on and awake for conventional manual focusing to be available.

This lens is well-suited for AF during video recording. The smooth focusing makes focus distance transitions easy on the viewer's eyes, and the camera's mic does not pick up the sound of the lens focusing.

A focus distance window is not provided on this lens (one is included on the EF III).

Canon super-telephoto lenses are not known to have the shortest minimum focusing distances among lenses in general. The good news is that the Canon RF 600mm F4 L IS Lens and the EF III improve upon the spec of the version II predecessor, dropping the close distance to 165.4" (4200mm) from 177.2" (4500mm). That line is great for marketing, but the less-exciting news is that the .15x maximum magnification spec is unchanged. This lens is an only-mediocre performer among all lenses in this regard.

Following is a comparison table showing the recent and current Canon super-telephoto lineup as of review time.

Model	Min Focus Distance "(mm)		Max Magnification
Canon RF 100-300mm F2.8 L IS USM Lens	70.9	(1800)	0.16x
Canon RF 100-500mm F4.5-7.1 L IS USM Lens	35.4	(900)	0.33x
Canon RF 200-800mm F6.3-9 IS USM Lens	31.5	(800)	0.25x
Canon RF 400mm F2.8 L IS USM Lens	98.4	(2500)	0.17x
Canon RF 600mm F4 L IS USM Lens	165.4	(4200)	0.15x
Canon EF 600mm f/4L IS III USM Lens	165.4	(4200)	0.15x
Canon EF 600mm f/4.0L IS II USM Lens	177.2	(4500)	0.15x
Canon EF 600mm f/4.0L IS USM Lens	216.5	(5500)	0.12x
Canon RF 600mm F11 IS STM Lens	177.2	(4500)	0.14x
Canon RF 800mm F5.6 L IS USM Lens	102.4	(2600)	0.34x
Canon RF 800mm F11 IS STM Lens	236.2	(6000)	0.14x
Canon RF 1200mm F8 L IS USM Lens	169.3	(4300)	0.29x
Sony FE 600mm f/4 GM OSS Lens	177.6	(4510)	0.14x

A subject measuring approximately 10.2 x 6.8" (259 x 173mm) will fill the frame at the minimum focus distance. The lily in the following image, captured at minimum focus distance, measures about 6" (152") in diameter.

Magnification from telephoto focal length lenses is not significantly increased with extension tubes, hollow tubes (with electronic connections) that shift a lens farther from the camera. This shift allows the lens to focus at closer distances, though at the expense of long-distance focusing. A 12mm extension tube increases the magnification range to 0.18-0.02x, and 0.21-0.05x results from mounting a 25mm extension tube. As of review time, Canon does not have RF mount-compatible extension tubes available, but third-party options are available. I used extension tubes with the IS version I lens a solid amount, especially when photographing birds and small mammals, but with the minimum focus distances decreasing on the version II and III lenses, I find less need for them.

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Extenders / Teleconverters

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As mentioned at the beginning of this review, the Canon RF 600mm F4 L IS USM Lens is compatible with the Canon RF 1.4x Extender and the Canon RF 2x Extender.

Lacking an EF mount, this lens is not compatible with the Canon Extender EF 1.4x III and the Canon Extender EF 2x III.

With the 1.4x behind it, this lens becomes an 840mm f/5.6 IS lens. With the 2x mounted, it becomes a 1200mm f/8 IS lens. Weather-sealing and image stabilization are included. The lens's native minimum focusing distance is retained with extenders in use, and that means the maximum magnification value is multiplied by the extender's multiplier, a significant improvement.

I didn't capture the following images with an extender focal length comparison in mind, but they work for that purpose.

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With the RF 1.4x behind the RF 600 L, image sharpness is decreased modestly (more than I like). Stopping down 1 stop to f/8 affects a minor improvement in sharpness, a combination of resolution and contrast. The 1.4x III adds a slight amount of barrel distortion but notably does not affect lateral CA.

As always, the image sharpness hit with the 2x is stronger than with the 1.4x, and 1200mm f/8 results are rather soft. The results at f/11, with the effects of diffraction beginning to show, appear similar to the f/8 results. Real-life results usually look better than our charts, but the 2x extender has a noticeable impact on image quality. The 2x increases lateral CA noticeably and barrel distortion slightly.

The with-extender autofocus performance I am experiencing is excellent. Unless the scene is extremely defocused, it is difficult to tell that the extender is even in place in regard to AF. Typically, low light performance can be decreased modestly with extenders reducing the maximum aperture.

Build Quality & Features

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Canon's big white super-telephoto lenses are among the most elite lenses available and represent the Canon L Series's best. Professionals expect these lenses to deliver the ultimate performance in the most adverse environments, and with the version III lens, the bar was raised. Despite the significant weight loss, the overall durability of the RF and EF version III lenses was increased over the already-impressive version II model.

Improvements in manufacturing processes get some of the credit for the enhancements, and fascinating is the use of a new carbon-reinforced magnesium alloy. "The high level of fluidity in this material enables injection molding (thixomolding) for a thin walled formation. For example, with the first group lens barrel on the 400mm model, we were able to achieve a barrel thickness of 0.8mm via injection molding, for a base that is 20% thinner than previous models, maintaining sufficient strength and lightness. The carbon reinforced magnesium alloy is also used for the tripod base plate and the exterior of the barrel." [Canon]

As lens size increases, the difficulty to maintain precision increases, and it has been interesting to see the attention to detail given to this lens.

Upon loading the standard product images for the Canon EF 600mm f/4L IS III USM Lens, the first side-by-side comparison I wanted to see was of the three 600mm f/4 IS versions.

At first glance, it appears that little has changed between the II (center) and III (left), but upon closer inspection, it seems that nearly everything has been changed. Hit the last link above to see larger versions of these images, but note that the tripod collar and foot have been moved significantly rearward, reflecting the much-improved weight distribution of this significantly lighter lens. The RF lens adds a built-in brushed aluminum mount adapter.

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At the mount end of the lens, there is little change from the version II lens. The AF/PF/MF switch and the focus limiter switch are easy to find and use in this location. The focus limiter switch gets a new number reflecting its reduced minimum focus distance.

The tripod collar lock knob got a new texture that is easier to roll between the thumb and finger. With the tripod collar shifted back, the main switch bank could be moved rearward for easier access. The switches available on the next switch bank have already been discussed, but notice the additional manual focus speed switch gained over the version II lens.

All of this lens's switches are mostly recessed, with just enough raised surface to be usable with gloves on. Note that the IS ON/OFF switch is raised in the center vs. both sides for tactile differentiation.

As already mentioned, the focus ring feels great, and the shape of this ring aids in the quality experience. The focus recall ring received a new, much-improved look and feel on the version III lens. The black grip ring also received a new diamond pattern that sticks to fingers.

Notably missing on this RF lens is a control ring.

You may have noticed that the RF and III lenses are slightly brighter in color than the II, which itself is much whiter than the version I lens. The color of this lens deserves additional attention.

Heat gain, especially uneven heat gain, can cause problems for a lens's optical performance, and big lenses have a lot of surface area to catch sunlight. Canon has chosen white paint to avoid as much heat gain as possible, and the new paint formulation on the III better shields the lens from heat than the previous paint did. "Infrared reflective pigments with high reflectance and titanium oxide lens barrel coating with silica provide excellent UV weather resistance and heat reduction." [Canon] But, that is just the beginning of the heat-avoidance efforts designed into the RF and version III lens.

A newly-developed heat shield coating reduces uneven heating, and a two-layer barrel structure design also helps mitigate thermal transfer effects into the lens elements. Reducing the weight of the lens naturally reduces its overall thermal capacity.

The RF and EF version III lenses have the same weather-resistant construction as the II series lens, which is excellent. Many outdoor events are held regardless of the weather, and the photographers required to cover them are forced to deal with the weather. While I recommend a rain cover when wet weather is expected, it is the unexpected that can be a bigger problem. I've used Canon weather-sealed super-telephoto lenses in some rather heavy rain with no ill effects. In addition to being sealed from moisture, dust is another hazard this lens keeps out.

The front and rear lens elements are fluorine-coated for easier cleaning and for preventing dust and drips from adhering in the first place.

You will immediately feel the ultra-high-quality construction when you pick up this lens. What you will also feel is the already-discussed significant weight loss from the version II lens. The difference is incredible. Carrying and using this lens causes less fatigue than when using the II predecessor, keeping the photographer sharp in the game. The lighter weight can reduce arm, back, and especially shoulder injuries that photographers commonly endure, and valuable is the easing travel weight restriction challenges.

This lens can easily be handheld for reasonable periods – for many hundreds of images in the IS testing segment of this review. Still, this is a 6.81 lbs. (3090kg) lens. Those used to the version II's weight will find this lens a feather-weight, but those using smaller lenses such as the Canon RF 70-200mm F2.8 L IS USM Lens will require a bit of acclimating.

The size of this lens garners attention. You look like you belong in some venues, and you will stand out in others. You'll get over the latter. Regarding the former, this lens is sometimes a ticket to access. This lens and others like it have gained me entrance to locations in venues that I would otherwise have been restricted from.

Here is a table of comparable Canon telephoto lenses with the weight specification included.

Model	Weight (lbs/)		Dimensions w/o Hood ("/)		Filter	Year
Canon RF 100-300mm F2.8 L IS USM Lens	5.84	(2650)	5 x 12.7	(128 x 323.4)	112	2023
Canon RF 100-500mm F4.5-7.1 L IS USM Lens	3.01	(1365)	3.7 x 8.2	(93.8 x 207.6)	77	2020
Canon RF 200-800mm F6.3-9 IS USM Lens	4.52	(2050)	4 x 12.4	(102.3 x 314.1)	95	2023
Canon RF 400mm F2.8 L IS USM Lens	6.37	(2890)	6.4 x 14.4	(163.0 x 367.0)	DI 52	2021
Canon RF 600mm F4 L IS USM Lens	6.81	(3090)	6.6 x 18.6	(168.0 x 472.0)	DI 52	2021
Canon EF 600mm f/4L IS III USM Lens	6.72	(3050)	6.6 x 17.6	(168.0 x 448.0)	DI 52	2018
Canon EF 600mm f/4.0L IS II USM Lens	8.65	(3920)	6.6 x 17.6	(168.0 x 448.0)	DI 52	2011
Canon EF 600mm f/4.0L IS USM Lens	11.83	(5360)	6.6 x 18.0	(168.0 x 456.0)	DI 52	1999
Sony FE 600mm f/4 GM OSS Lens	6.7	(3040)	6.4 x 17.7	(163.6 x 449.0)	DI 40.5	2019
Canon RF 600mm F11 IS STM Lens	2.05	(930)	3.7 x 10.6	(93 x 269.5)	82	2020
Canon RF 800mm F5.6 L IS USM Lens	6.92	(3140)	6.4 x 17	(163 x 432)	DI 52	2022
Canon EF 800mm f/5.6L IS USM Lens	9.85	(4470)	6.4 x 18.1	(163 x 461)	DI 52	2008
Canon RF 800mm F11 IS STM Lens	2.78	(1260)	4.0 x 14.2	(101.6 x 361.8)	95	2020
Canon RF 1200mm F8 L IS USM Lens	7.36	(3340)	6.6 x 21.1	(168 x 537)	DI 52	2022

For many more comparisons, review the complete Canon EF 600mm f/4L IS III USM Lens Specifications using the site's Lens Spec tool.

The RF 600 is light and handholdable, but I still prefer to use this lens on support for both comfort and stability reasons. Simply adjusting the monopod while tracking sports action is much easier with the lighter, rear-weighted lens. Also, it is easy and fast to lift the monopod off the ground to follow action handheld. Use the monopod to rest the setup between breaks in the action.

Use the site's product image comparison tool to visually compare the Canon RF 600mm f/4.0L IS USM Lens to other lenses.

The RF 600 F4 L IS utilizes the same 52mm drop-in filters as its predecessors and most of Canon's super-telephoto lenses. This lens's slot includes a drop-in filter holder that accepts 52mm threaded filters. A slim Canon Protect 52mm threaded filter comes installed (also helpful for catching dust before it drops deep inside the lens). Note that the filter is part of the optical design of Canon's big lenses, effectively the rear element in the lens design. The Canon Drop-In Circular Polarizing Filter PL-C 52 (WIII) is the filter option that will typically be found most helpful. This filter has had several revisions for color changes, keeping up with the lens color changes. Some will find neutral density filters helpful with this lens, especially when recording movies at f/4 under bright daylight.

With this lens's weight being comfortable for handholding, how this lens is handheld becomes a bigger issue. The shifted-rear weight distribution necessitated the tripod foot be moved back, and the tripod foot is the natural choice for holding this lens in use. The tripod foot height and the new rearward location combine to permit the left elbow to rest against the body for less shoulder strain. The version III foot's redesigned shape, including an upward curve at the end, makes handholding comfortable with fingertips ideally positioned for using the focus ring and the thumb located not far from the switches. The gripped padding provided on the tripod foot aids in carrying comfort.

This tripod foot has two differently-sized threaded inserts (1/4" and 3/8"). A Wimberley P50 Lens Plate permits quick attachment to Arca-Swiss compatible monopod and tripod head clamps. Mounting with two screws is important to prevent the plate from twisting, but note that most lens plates will require a 3/8"-16 to 1/4"-20 Reducer Bushing in the larger threaded insert. These are inexpensive, and it seems Canon could easily have included one in the box. Much better would have been to machine the needed Arca-Swiss dovetail grooves into the foot, as some other lens manufacturers have begun doing.

Replacing the Canon tripod foot with a Wimberley or Really Right Stuff Tripod Foot is popular and my preference.

The tripod collar is exceptionally smooth and provides light click-stops at 90°-degree rotations. While the click stops cause a slight bump during rotation (such as when panning with a subject as a monopod tilts), I prefer to have the click-stops assisting me with finding center, aiding significantly in keeping a camera level.

As the super-telephoto lenses continue to drop weight, the demands of the support they are used on also diminish. While this lens can be handheld for decent periods, you will still appreciate having support under the lens for longer periods of use (and for stabilizing the view). Avoiding future shoulder issues may not seem important today, but I assure you that you will one day appreciate having taken good care of your body in your youth. Keep your elbows in and shoulders at rest.

For tripod mounting, I suggest using a strong ball head (such as the Really Right Stuff BH-55 or Arca-Swiss Z1) with this lens. Much better (safer, easier) is to use a lens of this size on a gimbal style head such as the Wimberley WH-200-S Sidemount Head, Wimberley Tripod Head II, or Really Right Stuff PG-02.

Two tripod collar feet were included with the EF version II lens, with one being a small foot designed for monopods. I never used the small one, and apparently, many others left their small foot in the box as well. The smaller monopod base plate is reportedly again available for the RF lens, but it is now an optional accessory.

As first seen on the 600 IS II, the RF 600 F4 has a Kensington-type wire security lock under the tripod collar lock knob cap.

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The included ET-160 (WIII) lens hood is nearly the same as the version II lens's ET-155(WII) lens hood, with the paint color being the primary difference. This hood is relatively rigid, rather light (10.6 oz / 300g), and huge, offering the lens element excellent protection from bright light, impact, and the elements. While this hood is quite rugged, protect it as a replacement will cost as much as a nice lens.

The big lens hood is sometimes an issue from a space standpoint, including packing space and space on the sidelines or other events. For those circumstances, there is the optional Canon ET-160B Short Lens Hood. The price tag is substantial for this version also.

The EF 600mm f/4L IS version I lens came with a large leather-like lens cap that completely covered the reversed lens hood and was held in place with a drawstring that was not really needed as these covers were challenging to get off. The version II lens cap design was a huge improvement, featuring a shallower padded nylon cover that could easily be removed with one hand by simply pulling the hook-and-loop tab. That cap could be attached with the hood in ready-to-use or reversed positions and, if the Velcro tab was pulled tight enough, it could be attached directly to the lens without the hood being there. I doubt the latter feature was designed for, but the RF and version III lens's E-185C cap formally incorporates that feature. With an overall design similar to the version II cap, the version III cap adds a less padded, more flexible nylon extension with a drawstring that snugs around the end of a non-hooded lens. The front of the lens cap is additionally padded, with a rigid interior protecting the front lens element.

The included padded lens strap can be attached to the tripod ring, an attachment point that permits the camera to be rotated without the neck strap twisting around one's neck.

There is a new Canon super-telephoto lens case. Before the EF version III lens, Canon's super-telephoto lenses came in a rigid lens trunk. These shaped, lockable trunks were nice, protective, and good for storage, stacking, and shipping purposes. However, these trunks were expensive, often far oversized, could not hold a camera body, were not especially comfortable to shoulder carry, and rarely left my studio.

New with the RF and version III super-telephoto lenses is a sling-style (single strap) shoulder case, the Canon LS600 Soft Lens Case, replacing the trunk.

This nylon case looks great, is relatively compact and lightweight, well-padded, easy to use with smooth-functioning zippers and large pulls, and has a round molded-plastic bottom that keeps it upright on a flat surface. A thin zippered pocket and a pair of strap attachment points are provided on both sides of the case. The shoulder strap is padded and strong, and breathable padding is provided on the strap's case side, adding to the shoulder-carrying comfort. The convenient hand strap on top is also strong, with breathable padding ensuring that grip is not lost. Four hook-and-loop-adjustable pads are provided for interior use.

This case is nicely sized to hold its intended cargo.

Making the case large enough for a mounted camera to fit would have been a nice alternative. The additional cost would have been little (especially relative to the cost of the lens), and the utility of the case would have been greatly increased.

Transporting a large lens with a camera mounted increases the risk of damage, but there are many times when I'm transporting a lens such as this one in a lower-risk manner and prefer quick access to the mounted lens or want to avoid mounting a lens in unfavorable conditions. For example, arriving at a soccer (football for our friends across the pond) tournament and transporting the lens from field to field throughout the day can be low risk. Or, when photographing wildlife, getting the lens into action fast can mean the difference between getting the shot and getting nothing. For air travel or shipping, I usually separate the lens and body.

This case was designed to accommodate the slightly longer RF lens (the EF III is shown in the case pictured above).

The old 600B hard case weighs 9.6 lbs (4.35kg) empty, while the new LS600 weighs 2.2 lbs (2kg). That is another significant weight savings.

At review time, the MindShift Gear FirstLight 40L is my preferred carry case for this lens without a camera mounted.

Price, Value, Compatibility

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The Canon RF 600 F4 L IS USM lens's price will wow you as much as its image quality and overall performance. Without a doubt, the price is the biggest hurdle for getting this amazing lens into the hands of photographers wanting it (which is nearly all of them).

While this lens is expensive, it is priced in line with the other camera brand options. Canon USA's Rudy Winston shared some of the reasons for the high cost of this and similar lenses:

Fluorite lens elements: fluorite is an artificially grown crystal, not glass, and requires a lot of time to grow to sizes that can be used as lens optics. [In this regard, surely some cost savings was realized with the shifted-rearward fluorite elements being smaller in size] And then, it requires incredible skill and precision to cut and grind into shape for use as an optical element.

Mechanical design: these lenses require tremendous precision, to sustain optical alignment with their physical length and to withstand the inevitable bumps and bruises that they'll get in the hands of working professionals. This is easy to take for granted, but they're much more difficult to manufacture than smaller, lighter lenses.

Skill of manpower used for assembly: usually, the most skilled and experienced workers are culled for assembly of the big white super-tele lenses (along with the Cinema EOS lenses), AND these lenses tend to be largely hand-assembled. The costs associated with this are, of course, absorbed into the final selling price of the lens.

Finally, you have simple economies of scale... even if the price was arbitrarily cut in half, we know the number of units sold per year would never match those of lighter, more everyday pro-level lenses (think of 70-200/2.8s, 24-70/2.8s, and so on). So the development costs and so on, again, have to be made up with fewer total lenses being sold during the product's lifetime.

Fortunately, quality lenses hold their value well. While the overall cost of ownership for these lenses can vary greatly (including the effects of monetary exchange rate fluctuations), a Canon super-telephoto lens can typically be sold for a solid percentage of the purchase price. The concept of buying this lens to photograph a child's high school sports career and later selling it to fund their college education seems logical. Those pursuing professional wildlife or sports photography will likely find the Canon EF 600mm f/4L IS III USM Lens a career requirement.

If the price makes the RF 600mm F4 unobtainable for you, consider renting one for your special events. If you are not shooting professionally, consider getting other parents to share in the rental expense in exchange for photos of their kids participating in sports.

As expensive as this lens is, you get what you pay for. Also, consider that price is a barrier for entry, meaning skilled photographers with this lens have a competitive advantage that will not be overcome by the masses with a camera.

As an "RF" lens, the Canon RF 600mm F4 L IS USM Lens is compatible with all Canon EOS R-series cameras. Canon USA provides a 1-year limited warranty.

The reviewed Canon RF 600mm F4 L IS USM Lens was purchased online-retail.

Alternatives

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Building a mount adapter into a lens does not change its image quality. That means the Canon EF 600mm f/4L IS III USM Lens and the Canon RF 600mm F4 L IS USM Lens are equals in that regard. However, the RF mount technology increases the CIPA image stabilization assistance rating to 5.5 stops from 5.0 stops.

The Canon RF 600mm F4 L IS USM Lens vs. Canon EF 600mm f/4L IS III USM Lens comparison shows the RF lens slightly longer and slightly heavier. Add the Canon Mount Adapter EF-EOS R into the equation, and the reverse is true.

The EF lens can mount on a DSLR, while the RF lens cannot. The EF lens has a focus distance window vs. having the distance only available on the LCD or EVF. The two lenses are priced identically.

If you have migrated to mirrorless cameras, get the RF lens. Upgrading from an EF 600mm F4 III lens currently in the kit is considerably harder to justify.

Should I get the Canon RF 600mm F4 L IS USM Lens or the Canon RF 400mm F2.8 L IS USM Lens?

Obvious and significant are that 400mm and f/2.8 are significantly wider than 600mm and f/4. Also key to this comparison is that adding the Canon RF 1.4x to the RF 400 makes it a 560mm f/4 lens, nearly equalizing the 600mm lens's primary advantage.

At their wide-open apertures, these two lenses turn in nearly perfect results in the image quality comparison. At f/4, the 400mm lens is even slightly sharper. Extenders impact image quality, and with the RF 1.4x behind the RF 400mm lens, the 600mm vs. 560mm image quality comparison shows the RF 600 sharper in the center of the frame. However, the center differential is not substantial, and the two lenses compare similarly in the mid-frame and periphery.

The 400mm lens has slightly stronger pincushion distortion and slightly stronger barrel distortion at 560mm.

The Canon RF 600mm F4 L IS USM Lens vs. Canon RF 400mm F2.8 L IS USM Lens comparison shows the 400mm lens slightly lighter and considerably shorter. The RF 1.4x addition equalizes the weight but subtracts only slightly from the length difference. Natively, both lenses have .17x maximum magnification, but the RF 400 focuses considerably closer, an advantage that holds with the 1.4x mounted. The RF 400 is less expensive by a significant amount, though the percentage difference doesn't seem as great. Adding the RF 1.4x to the equation brings the two options closer.

If you need the 400mm angle of view, the choice is easy. Get the 400mm lens. With equivalent subject framing, the 400mm lens will produce the same impressive background blur as the 600mm lens at f/4, but the 1-stop lower ISO setting will produce considerably lower noise levels in low light. For wildlife, I usually take the 600mm option. When sports permit a close enough vantage point, I take the 400mm lens. Getting both lenses is the optimal solution, but doing so requires a significant financial investment.

Those open to other brand cameras should consider the Sony FE 600mm f/4 GM OSS Lens.

In the image quality comparison, the two lenses turn in equivalent outstanding performance. The Sony lens is remarkably sharp with extenders mounted, having the advantage in this comparison. The Canon lens has slightly less peripheral shading and slightly less pincushion distortion.

We find the two lenses weighing nearly identical amounts in the Canon RF 600mm F4 L IS USM Lens vs. Sony FE 600mm f/4 GM OSS Lens comparison. The Sony lens (and lens hood) is slightly smaller and has 11 aperture blades vs. 9. The Canon lens has a slightly higher maximum magnification (0.17x vs.0.14x), and I find the Canon lens's image stabilization system to be more effective than the Sony's in the field. The Canon lens costs $1.00 more than the Sony lens at review time.

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

Summary

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The Canon RF 600mm F4 L IS USM Lens, created by a company with a long history of delivering the best-available camera lenses, is the ultimate wildlife and sports lens. As those pursuits are frequent for me, this is one of the most used lenses in my kit.

Essentially the same as the Canon EF 600mm f/4L IS III USM Lens, the RF 600 F4 lens is a roll-up of the best technology, including that in the lens's design and the innovative manufacturing techniques required to make it a reality for the professionals ultimately relying on it.

This lens features superb build quality, a long super-telephoto focal length, an ultra-wide aperture for that focal length, high-performing image stabilization, and a fast and precise AF system. The RF 600 F4's image quality is outstanding, as is the look that the 600mm focal length and f/4 aperture combine to create.

The built-for-speed RF 600mm F4 L IS USM package works exceedingly well for serious, discerning sports photographers, wildlife photographers, and photojournalists. This lens will have under-funded photographers digging through their gear kits search for anything that might be considered non-essential and potentially contributable to the 600mm F4 L IS fund. Once the investment challenge has been overcome, taking delivery of a new Canon super-telephoto lens makes even the most jaded photographer feel like a kid on Christmas morning.