Let me introduce you to Canon's ultimate wildlife and big field sports lens, the EF 600mm f/4L IS III.
If you can get past the price, the EF 600mm f/4L IS III Lens will blow you away in most other regards. This is one of the most incredible lenses available and the ultimate big field action sports lens. The 600 f/4 IS III features an impressive design, superb image quality, incredibly fast AF, and best-available build quality.
As the Canon EF 400mm f/2.8L IS III USM Lens is to the Canon EF 400mm f/2.8L IS II USM Lens, the Canon EF 600mm f/4L IS III USM Lens is to the Canon EF 600mm f/4.0L IS II USM Lens, and these two reviews will mirror each other in many regards. The EF 600mm f/4L IS III USM Lens is the 6th generation in Canon's 600mm f/4 series, replacing the introduced-in-2011 Canon EF 600mm f/4L IS II Lens, and the 3rd IS version. Owners of this lens will, like owners of the previous lens versions, primarily be professional and serious amateur photographers (or simply wealthy). Due to the focal length and max aperture of this lens, these photographers will primarily use this lens for sports, wildlife, and photojournalistic pursuits.
As with the 400 L III, the bar was set extremely high for the 600 L III. This lens' predecessor was simply 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 totally new lens design with the most obvious difference being dramatically lighter weight. While photographers have many opinions about what they want in a lens, universal for this one was a desire for 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 7 years later. But, that was delivered.
Let's put the Canon super telephoto weight loss program into a chart:
|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 EF 600mm f/4L IS III USM weighs only approx. 6.7 lbs (3,050g). That is approximately 1.9 lbs (870g) less than the II (22% less) and a whopping 5.1 lbs (2,310g) less than the I lens (43% less).
Upon the curtain going up at the announcement event for this lens (Elliot Peck, Canon USA Senior VP & GM shown above), I walked straight up to the 600 III and the simultaneously-introduced Canon EF 400mm f/2.8L IS III USM Lens and held both versions of the 600 at the same time. I was blown away. The difference felt even more significant than the numbers show and part of the reason for this is because the weight has been shifted rearward, giving the lens a better balance. The improvements in these regards alone are quite dramatic.
So, how did the weight savings and improved balance come about?
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, but aside from being somewhat longer, the 600mm designs mirror the 400mm designs for each respective generation of lens, meaning that this illustration is representative to 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 savings 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. This design also moved the center of gravity rearward for a more-comfortable and better-handling design as the front of the lens gets moved the most and it is now much lighter (though with decreased momentum, the new lens is not as easy to hold in place).
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."
Also interesting is that this lens along with the 400 f/2.8L IS III are 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."
Another interesting design element is the aperture that is moved forward, resulting in the largest EMD (electromagnetic diaphragm) in an EF lens to date and representing another design challenge Canon had overcome.
Those are the headlining Canon EF 600mm f/4L IS III Lens improvements addressed.
While this lens is amazing in many ways, it is the 600mm super telephoto focal length that you should be especially interested in and note that, despite the size and cost of this lens, it provides a similar angle of view as all of the other (accurately-denoted) 600mm lenses (including zoom lens options). What is the 600mm focal length's very narrow angle of view commonly used for?
When you need to frame a subject tightly and can't get closer, due to ...
... you might need a 600mm lens.
If you simply don't want to get closer, including for comfort reasons or avoiding impact to wildlife behavior, a 600mm lens might be just right. Sit in the comfort of your car, avoid the need to cross 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 the 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 coming soon) is a great complement to the narrow angle of view. The light weight of this lens along with the long focal length makes it a good choice even for birds-in-flight.
The image above was captured with the version II lens. Canon provides a wildlife-friendly 800mm lens option with a 1-stop-narrower max aperture, but the 600 f/4L IS III exceeds that focal length at the same aperture with a 1.4x extender mounted behind it.
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 this lens' reach. When photographers covering events are not permitted close access to their subjects, including at concerts, speaking events, etc., this focal length will often provide the reach needed. This lens is a great choice for photographing air shows, especially when single aircraft are flying.
The 600mm focal length used on smaller APS-C/1.6x (FOVCF) imaging sensor format cameras provides a very narrow angle of view, equivalent to a 960mm lens on a full frame camera. This much narrower angle of view diminishes the scenarios this lens is ideally suited for. I rarely hear a bird photographer complaining about having too much focal length. However, this angle of view is challenging to use at many sports events (keeping a subject in the frame at this angle of view is challenging) and it is even too long for some wildlife photography. Moving back can be an answer, but obstacles can get in the sight path and longer distance means that heat waves are more likely to be an issue.
While on the heat waves 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 best techniques.
When present, heat shimmer/haze/waves will create optical distortion that will diminish the quality of long-distance photos and I encounter this issue with some frequency. My first use of the 600 L IS III lens was at a soccer tournament held at an impressive venue featuring all artificial turf fields. While the sunny weather made this spring event remarkably comfortable to watch, sun on artificial turf spells doom for image quality. Looking across the field, I could see the white field lines dancing in the heat waves. I knew that my images were all going to be compromised and ... they were, including the sports sample image shared above (see the strange background blur?). This was a scenario were a 400mm lens would have delivered better (roughly 1/3 better) image quality with ideally-framed subjects (they would have had to be closer) as there would have had less turbulent air at 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 action from a fixed position, as is very frequently the case with sports photography. A longer focal length lens has a narrower angle of view, which of course 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 in which to capture an optimally-framed subject. That advantage can result in less cropping needed with higher resolution retained.
Explaining that concept ... if you are photographing a running person with a 24mm lens on a full frame format DSLR, 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 optimal to optimal distance than the 24mm lens' 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 greater amount of time 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 does not mean that a 600mm lens is always a better choice, but it is definitely the 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 larger areas of optimal coverage. However, these longer lenses do not offer the big f/4 aperture advantage and again, the angle of view at 800mm is narrow enough to make keeping a fast-moving subject properly framed challenging.
Here is an example of the 300-600mm focal length range captured by a zoom lens (the 600mm sample might be a touch wider angle of view than it should) as seen by a full frame camera:
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 being used).
I wouldn't buy this lens specifically for photographing landscapes, but if you have this lens, landscapes, flowers, and many other subjects can be captured with 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 below was captured with the version II lens.
The 600 f/4L IS III has the longest focal length available in a lens with an f/4 max aperture. I mentioned that there were other 600mm lenses and that some of those had a zoom focal length range advantage but none of the zoom options have an f/4 aperture available and that is a huge differentiator. The one stop (or more) difference between this lens and the alternatives is big, big 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. The Canon EF 600mm f/4L IS III lens' huge f/4 aperture is the biggest contributor to the large size, heavy weight (though much lighter now), and high cost of this lens, but it is also key to its awesomeness.
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 the f/4 feature and 600mm combined with f/4, via shallow depth of field combined with strong telephoto magnification, delivers one of the strongest background blurs available in any lens. Use this lens to blur the background, turning advertisement banners, fans, and their clothing, apparatus, gear, seating, etc. into just blurs of color, making the subject stand out, popping from the frame. 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. Look at the images in the popular sports magazines/websites and you will see the results this lens can achieve.
The f/4 aperture can markedly differentiate your work from the crowd. When using this lens (or its predecessors), I use f/4 far more than any other aperture and could probably be happy with only f/4 in this lens.
Despite the f/4 aperture being so huge in a 600mm lens, it may still not be adequate for photographing sports under (normal) field lighting at night or indoors where an f/2.8 aperture may prove to be the minimum aperture desired and the Canon EF 400mm f/2.8L IS III USM Lens may be the better choice for those environments.
The other sensor that works better with the large amount of light provided by this lens' aperture is a camera's AF sensor.
Here is a look at a range of 600 f/4 apertures as seen by the version II lens:
The widest apertures create a great background blur while the narrower apertures keep more of this close young whitetail deer in focus.
Practically everything in this lens is new and that includes the image stabilization system that has achieved an impressive up-to-5-stop CIPA rating. Borrowed for this system are the vibration gyro and latest microprocessor from the Canon EF 70-200mm f/4L IS II USM Lens, though these were tuned specifically for the characteristics of the 600 III.
This lens is far lighter than its predecessor, but it is still not a light lens to handhold and handholding it 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. What I learned was 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 were made at even longer exposures.
Keep in mind that this 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 closer proximately of pixel wells.
As with the version II lens, three IS modes are present. Mode 1 is the general-purpose mode and the latest word I've heard from Canon is that this mode should be used for nearly all situations including while using a tripod, monopod, and while photographing action.
Mode 2 IS is used for panning with a subject. In this mode, only 1 axis of stabilization is provided, allowing the linearly-moving subject to be tracked.
Mode 3 is used for tracking action, especially fast-moving erratic action. In mode 3, 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 an erratic subject 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 will only apply Image Stabilization at right angles to the direction of the detected movement (like IS Mode 2).
A noticeable click is heard when IS starts and again when it stops, but only very quiet whirring and clicking are audible while IS is active. This IS implementation is extremely 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 being used and attempts to eliminate mirror slap, shutter and tripod vibrations. "The new IS unit features improved high-frequency tracking performance, so it is better equipped to handle mirror slap when using a tripod compared to the current II series." [Canon]
While stopping camera motion-induced image blur is image stabilization's primary job, it has another significant benefit and that is 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 at action-stopping shutter speeds and AF precision is especially critical with the 600mm f/4 combination producing a potentially very shallow depth of field.
Update: the following issue has been addressed via a firmware update. Note that a 600mm III lens image stabilization problem was being reported by, initially, some 5D Mark IV and other camera users. Reportedly, this lens produced a ghost-like blur at longer shutter speeds when shooting through the viewfinder with IS enabled. Initial reports indicated that 1/250 or 1/200 and longer shutter speeds produced this effect and further reports specify that the blur disappeared at 1/250 and only longer shutter speeds are concerned (1/160 was reportedly the worst). Again, this issue has been addressed by firmware update v1.1.2.
I relied on the 2-stop-rated IS system when using the version I 600mm f/4L IS lens, especially when shooting wildlife. But, I didn't handhold that lens a lot due to its shoulder/back injury-inviting weight. That lens' tripod-sensing IS system was quite helpful in reducing vibration (including from mirror slap) when shooting from a tripod, but handholding the version II lens was much easier, the 4-stop-rated system was much improved, and I began relying on IS much more frequently. With the huge additional weight loss, the version III lens can now be handheld for significantly longer periods of time and the improved 5-stop image stabilization system greatly extends this lens' versatility in that regard.
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, right? With the version II lens delivering incredible image quality, there was very little room for improvement with the III and few would be anxious to see any decline in image quality despite the weight reduction.
Let's start with a look at the Canon-supplied theoretical MTF charts.
The version II lens has awesome image quality and the version III promises nearly identical results.
We lab-tested three copies of this lens. The first results were thrown out with the lens deemed damaged. The second sets of results were not quite identical to the version II lens as expected based on the MTF charts, so a third lens was brought in for testing. The third lens performed very similarly to the second lens.
The f/4 aperture is critically important to this lens. 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 sharp in the center of the frame and impressively sharp in the mid and periphery of the full frame image circle. Little benefit is seen by stopping the aperture down.
The version III vs. II comparison shows the version II lens very slightly sharper in the center of the frame with the difference becoming more apparent when extenders are mounted. The version III lens has considerably less lateral CA.
Our lab sharpness tests tell the story the best, but I attempted to create some outdoor comparison examples to share. To be accurate, the stable lighting of a clear sky is needed for this testing and heat waves are often present when the sky is clear. When magnified with a 600mm lens, heat waves prevent accurately 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 even modestly-high sharpness settings are destructive to image details and hide the true characteristics of a lens.
Be sure to find the center of the plane of sharp focus 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 plane of sharp focus 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.
Friends reporting from the field are very happy with the results they are getting from the 600 L III.
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 very 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 there is practically no shading whatsoever at narrower apertures.
APS-C format camera owners will not likely notice the about-0.6-stops of shading at f/4.
The effect of different colors of the spectrum being magnified differently is referred to as lateral (or transverse) CA (Chromatic Aberration). 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 greatest amount as this is where the greatest difference in the magnification of wavelengths exists. Any color misalignment present can easily be seen in the site's image quality tool, but let's also look at a worst-case example, a 100% crop from the extreme top left corner of a 5Ds R frame.
There should be only black and white colors in this image and that is essentially what we see here. This lens shows a very small 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, or 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 look for. Axial CA remains at least somewhat persistent when stopping down with the color misalignment effect increasing with defocusing while 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 silver jewelry in the 100% crops above show a slight color difference in the foreground vs. background and the details in the center of depth of field are very 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 one 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. I doubt that you'll ever be tempted to distortion-correct a Canon EF 600mm f/4L IS III 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:
The f/8 examples show performance that is normal and the "Cat's Eye" example, showing the top corner from the rightmost 1/3 of the frame where circular specular highlights in f/4 results become squeezed.
How good is the optical quality of the Canon EF 600mm f/4L IS III Lens? Overall, it is remarkably good. That the version II lens is so impressively sharp is really the only negative attribute I have for the version III lens.
Critical for the success of a lens with very shallow depth of field being used primarily to photograph fast action is its AF performance. Canon's super telephoto lenses have long delivered best-available autofocus performance and this lens continues that trend.
As you would expect, this lens gets all of the latest-available upgrades. "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. Note that Canon specifically mentions that the "EOS-1D and EOS 5D series benefit from improved AF performance when used with the III series lenses."
In addition to being fast and accurate, this lens' internal AF system is very quiet. Some quiet internal shuffling along with quiet clicks can be heard if you listen carefully, but I don't even notice the sounds when shooting.
The IS version II and III super telephoto lenses include a Focus Preset feature. Set the Focus Preset to a specific distance and when your shooting needs require that specific 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 III is 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' focus distance range. In addition to the full range, restricted limits of 13.8' — 52.5' (4.2m — 16m) and 52.5' (16m) — ∞ can be selected for improved focus lock times and reduced focus hunting when photographing subjects at distances 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 I like to use a focus-and-recompose technique with static subjects during the event. The autofocus stop feature makes it easy to obtain focus lock, turn off autofocus and recompose for a framing that places the active focus point(s) off of the subject, including in the periphery of the frame. Another great use for this feature is when an image has been captured but the framing is not optimal. Simply press a focus stop button and capture enough images to be stitched together during post-processing. Of course, switching the lens to manual focus mode also works for these techniques.
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 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 (very) slightly to get the low speed electronically-driven AF and turn it to a greater degree to obtain a higher speed with the direction of ring rotation determining the direction of focus distance change. The feature works nicely, but you are going to need a solid tripod setup and a steady hand to not 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 – this ring lens provides a superb manual focus experience. Instead of a conventional mechanically-linked manual focus drive, Canon implemented electronic manual focusing in this lens, the first Canon super telephoto (along with the 400mm f/2.8L IS III) to have such. This decision simplified the overall design, saving weight and increasing expected reliability. Perhaps your first clue about this being a focus-by-wire design will be when attempting to manually focus with the camera powered off or the metering inactive. This no longer works.
This lens' manual focus ring is ideally located, large in size, has a sharply-ribbed rubber surface with a great feel and ideal rotational resistance, and is very 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 feature 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 focus more-slowly than on the II series and mode 2 and 3 become respectively slower still for very fine control over focusing. You don't want to use the 3 setting to chase sports action, but this mode does allow for very precise manual focusing.
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 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' switch must be in the "MF" position and the camera meter must be on and awake for conventional manual focusing to be available.
Cameras featuring Dual Pixel CMOS Movie Servo AF make video recording very easy and this lens is very well-suited for this task. The smooth focusing makes focus distance transitions easy on the viewer's eyes and the sound of the lens focusing is not picked up by the camera's mic.
A focus distance window is provided with this lens.
Canon super telephoto lenses are not known to have the shortest minimum focusing distances. The good news is that the Canon EF 600mm f/4L IS III Lens improves upon the spec of its 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 and 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.
|Canon EF 200mm f/2.0L IS USM Lens||74.8"||(1900mm)||0.12x|
|Canon EF 200-400mm f/4L IS Ext 1.4x Lens||78.7"||(2000mm)||0.15x, 0.21x|
|Canon EF 300mm f/4.0L IS USM Lens||59.1"||(1500mm)||0.24x|
|Canon EF 300mm f/2.8L IS II USM Lens||78.7"||(2000mm)||0.18x|
|Canon EF 100-400mm f/4.5-5.6L IS II USM Lens||38.4"||(975mm)||0.31x|
|Canon EF 400mm f/5.6L USM Lens||137.8"||(3500mm)||0.12x|
|Canon EF 400mm f/2.8L IS III USM Lens||98.4"||(2500mm)||0.17x|
|Canon EF 400mm f/2.8L IS II USM Lens||106.3"||(2700mm)||0.17x|
|Canon EF 400mm f/2.8L IS USM Lens||118.1"||(3000mm)||0.15x|
|Canon EF 400mm f/4 DO IS II USM Lens||129.9"||(3300mm)||0.13x|
|Canon EF 500mm f/4.0L IS II USM Lens||145.7"||(3700mm)||0.15x|
|Canon EF 600mm f/4L IS III USM Lens||165.4"||(4200mm)||0.15x|
|Canon EF 600mm f/4.0L IS II USM Lens||177.2"||(4500mm)||0.15x|
|Canon EF 600mm f/4.0L IS USM Lens||216.5"||(5500mm)||0.12x|
|Canon EF 800mm f/5.6L IS USM Lens||236.2"||(6000mm)||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 the use of extension tubes, hollow tubes (with electronic connections) that shift a lens farther from the camera, but all Canon super telephoto lenses are compatible with these. This shift allows the lens to focus at closer distances, though at the expense of long-distance focusing. The Canon EF 12mm Extension Tube II increases the magnification range to 0.18-0.02x and 0.21-0.05x is the result of mounting a Canon EF 25mm Extension Tube II. 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 using them.
This lens is compatible with the Canon Extender EF 1.4x III and the Canon Extender EF 2x III, but note that Canon has indicated that the version III 600mm f/4L IS and 400mm f/2.8L IS lenses are not compatible with previous version I or II Canon EF extenders (a first for an L-lens). The resulting focal length and aperture combinations of this lens being used with extenders (often referred to as teleconverters) are quite impressive. With the 1.4x, this lens becomes an 840mm f/5.6 IS lens and with the 2x, it becomes a 1200mm f/8 IS lens. Weather-sealing and image-stabilization are included. The 1.4 combination autofocuses on all current Canon EOS bodies, the f/8 combination autofocuses on select models (with a reduced number of AF points available), and both combinations focus on all currently available imaging sensor-based AF systems. The lens' native minimum focusing distance is retained 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.
With the EF 1.4x III behind the 600 L III, image sharpness is decreased moderately in the center (the corners are less-affected) with a wide-open aperture. Stopping down 1 stop to f/8 brings a nice improvement in sharpness and results at this aperture are very sharp. The 1.4x III adds a bit of barrel distortion and a minor amount of 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 are slightly improved at f/11 with the effects of diffraction showing at narrower apertures. Real life results usually look better than our charts, but the 2x has a noticeable impact on image quality. The 2x increases lateral CA more than the 1.4x does, but the with-2x linear distortion profile looks better.
In decent light, the with-extender autofocus performance is excellent. It is hard to tell that the extender is even in place in regards to AF. Typically, low light performance can be decreased modestly with extenders reducing the maximum aperture.
"To get the best out of the new lenses and the Mark III extenders, photographers must ensure they attach the extender to the lens first, before attaching the whole unit to the camera. This ensures that the combined lens information is transmitted correctly to provide the optimum image quality and focus performance." [Canon Europe CPN]
Canon's big white super telephoto lenses are among the most elite DSLR lenses available and represent the best of the Canon L Series. Professionals expect these lenses to deliver the ultimate performance in the most adverse environments and this one raises that bar. Despite the significant weight loss, the overall durability of the 600 f/4L IS III has been increased over the already-impressive previous model.
Improvements in manufacturing processes get some of the credit for the enhancements and very interesting 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 especially note that the tripod collar and foot have been moved significantly rearward, reflecting the much-improved weight distribution of this much lighter lens.
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 gets a new texture that is easier to roll between the thumb and finger. With the tripod collar shifted back, the main switch bank was also able to 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' 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 has a new, much-improved look and feel. The black grip ring has a new diamond pattern that sticks to fingers.
You may have noticed that the III is slightly brighter in color than the II, which itself is much whiter than version I. The difference is also noticeable in the images showing the previous-white-version extenders mounted. The color of this lens deserves additional attention.
Heat gain, especially uneven heat gain, can cause problems for a lens' 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 better shields the lens from heat than the previous paint did. But, that is just the beginning of the heat-avoidance efforts designed into this lens.
A newly-developed heat shield coating reduces uneven heating and a two-layer barrel structure design also helps mitigate effects of thermal transfer into the lens elements. Reducing the weight of the lens naturally reduces its overall thermal capacity.
The version III lens has the same weather-resistant construction as the II series lens which is really good. Many outdoors events are held rain or shine and those required to photograph them are not given a choice about the weather. While I use and recommend a rain cover when wet weather is expected, it is the unexpected that can be a 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.
When you pick up this lens, you will immediately feel the ultra-high-quality construction. What you will also feel is the already-discussed very significant weight loss. The difference is amazing. Carrying and using this lens causes less fatigue than when using its predecessor, keeping the photographer sharp in the game. The lighter weight can reduce arm, back, and especially shoulder injuries photographers commonly endure and also valuable is the easing travel weight restriction challenges.
This lens can easily be handheld for reasonable periods of time – for many hundreds of images in the case of the IS testing segment of this review. Still, this is a 6.72 lbs. (3050kg) lens. Those used to the version II's weight will find this lens to be a feather-weight, but those using smaller lenses such as the Canon EF 70-200mm f/2.8L IS III 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. 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/g)||Dimensions w/o Hood ("/mm)||Filter||Year|
|Canon EF 200mm f/2.0L IS USM Lens||5.56||(2520)||5.0 x 8.2||(128 x 208)||DI 52||2008|
|Canon EF 200-400mm f/4L IS 1.4x Lens||7.98||(3620)||5.0 x 14.4||(128 x 366)||DI 52||2013|
|Canon EF 300mm f/4.0L IS USM Lens||2.63||(1190)||3.5 x 8.7||(90 x 221)||77||1997|
|Canon EF 300mm f/2.8L IS II USM Lens||5.19||(2350)||5.0 x 9.8||(128 x 248)||DI 52||2011|
|Canon EF 100-400mm f/4.5-5.6L IS II USM Lens||3.51||(1590)||3.7 x 7.6||(94 x 193)||77||2014|
|Canon EF 400mm f/2.8L IS III USM Lens||6.27||(2840)||6.4 x 13.5||(163 x 343)||DI 52||2018|
|Canon EF 400mm f/2.8L IS II USM Lens||8.49||(3850)||6.4 x 13.5||(163 x 343)||DI 52||2011|
|Canon EF 400mm f/2.8L IS USM Lens||11.85||(5370)||6.4 x 13.7||(163 x 349)||DI 52||1999|
|Canon EF 400mm f/4 DO IS II USM Lens||4.63||(2100)||5.0 x 9.2||(128 x 233)||DI 52||2014|
|Canon EF 400mm f/4 DO IS USM Lens||4.28||(1940)||5.0 x 9.1||(128 x 232)||DI 52||2001|
|Canon EF 400mm f/5.6L USM Lens||2.76||(1250)||3.5 x 10.1||(90 x 257)||77||1993|
|Canon EF 500mm f/4.0L IS II USM Lens||7.04||(3190)||5.7 x 15.1||(146 x 38m)||DI 52||2011|
|Canon EF 600mm f/4L IS III USM Lens||6.72||(3050)||6.6 x 17.6||(168 x 448)||DI 52||2018|
|Canon EF 600mm f/4.0L IS II USM Lens||8.65||(3920)||6.6 x 17.6||(168 x 448)||DI 52||2011|
|Canon EF 600mm f/4.0L IS USM Lens||11.83||(5360)||6.6 x 18.0||(168 x 456)||DI 52||1999|
|Canon EF 800mm f/5.6L IS USM Lens||9.86||(4470)||6.4 x 18.1||(163 x 461)||DI 52||2008|
For many more comparisons, review the complete Canon EF 600mm f/4L IS III USM Lens Specifications using the site's Lens Spec tool.
It is light and handholdable, but I still prefer to use this lens on a 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, lifting the monopod off the ground to track action handheld is easy and fast to do. Use the monopod to rest the setup between breaks in the action.
Putting the sizes into perspective:
Positioned above from left to right are the following lenses:
Notice the slightly whiter color of the III?
The same lenses are shown below with their hoods in place.
Like most of Canon's super telephoto lenses, the 600 f/4L IS III utilizes the same 52mm drop-in filters as its predecessors. Included in this lens' slot is a drop-in filter holder that accepts 52mm threaded filters. A Canon Protect 52mm filter comes installed (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 useful. This filter has had several revisions for color changes, keeping up with the lens color changes. Some will find neutral density filters to be useful with this lens, especially when recording movies at f/4 under bright daylight.
With this lens' weight being comfortable for handholding, how this lens is handheld becomes a bigger issue. The shifted-rear weight distribution required the tripod foot to be moved back and the tripod foot is the natural choice for holding this lens in use. The height of the tripod foot combined with the new rearward location combine to keep the left elbow resting against the body for less shoulder strain. The redesigned shape of the foot, 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"). As you see in the product images on this page, I have a Wimberley P50 Lens Plate attached to my lens for quick attachment to my 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 very 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 started doing.
The tripod collar is extremely smooth and provides light click-stops at 90°-degree rotations. While the click-stops cause a small bump during rotation (such as when panning with a subject as a monopod tilts), I much 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 of time, 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 Tripod Head II or Really Right Stuff PG-02. The 600mm IS III is shown mounted to the RRS FG-02 head with an RRS Ground-Level Tripod under it in many of the product images on this page.
Two tripod collar feet were included with the 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 version III lens, but this time it is an optional accessory.
As first seen on the 600 IS II, the 600mm IS III has a Kensington-type wire security lock under the tripod collar lock knob cap.
The included ET-160 (WIII) lens hood is nearly the same as the version II lens' ET-155(WII) lens hood with paint color being the primary difference. This hood is relatively rigid, rather light (10.6 oz / 300g) and very large, 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 both packing space and space on the sidelines or other event. For those circumstances, there is the optional Canon ET-160B Short Lens Hood. The price tag is rather strong for this one 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 difficult 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. The 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 that latter feature was designed-for, but the version III formally adds that feature. With an overall design similar to the version II, the version III cap adds a less-padded, more-flexible nylon extension with a draw-string 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 allows the camera to be rotated without the neck strap following the rotation (otherwise causes strangulation).
There is a new Canon super telephoto lens case. For as long as I can remember, Canon's super telephoto lenses came in a rigid lens trunk. These shaped, lockable trunks were very nice, very protective, and were 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 version III 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, is well-padded, is 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 two 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 case side of the strap, 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 DSLR to fit would have been an alternative. The additional cost would have been very 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 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.
For those who love the trunk style case (and the ability to stack them), Canon has you covered. The Canon 600C Lens Case is available, but brace yourself before looking at the price. And, take good care of your LS600, because it also has a very big price tag itself.
The old 600B hard case weighs 9.6 lbs (4.35kg) empty. The new LS600 weighs 2.2 lbs (2kg). That is another very big weight savings.
At review time, the MindShift Gear FirstLight 40L is my preferred carry case for this lens. This lens with a pro body mounted just fits into this excellent backpack.
The price of the Canon 600 f/4L IS III lens 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 from monetary exchange rate fluctuations), a Canon super telephoto lens can typically be sold for a solid percentage of the purchase price. I cannot promise anything in this regard (I even made a considerable profit when selling the version I IS lenses). The concept of buying this lens to photograph a child's high school sports career and later selling it to help fund their college education seems logical. Those pursuing professional wildlife and/or sports photography will likely find the Canon EF 600mm f/4L IS III USM Lens to be a career requirement.
If the price makes the Canon EF 600mm f/4L IS III USM Lens 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 "EF" lens, the Canon EF 600mm f/4L IS III USM Lens is compatible with all Canon "EOS" cameras (the EOS "M" and "R" series models require an adapter). Canon USA provides a 1-year limited warranty.
The reviewed Canon EF 600mm f/4L IS III USM Lenses were online-retail sourced.
Throughout this review, the differences between the Canon EF 600mm f/4L IS III USM Lens and the Canon EF 600mm f/4.0L IS II USM Lens have been discussed with the III's huge weight reduction being a primary differentiator. My experience to date gives the version II lens a slight image sharpness advantage with the III having noticeably less lateral CA.
Looking at the specs and measurements, the Canon EF 600mm f/4L IS III vs. II USM Lens comparison shows, primarily, the weight loss but also that the III picks up a 1-stop higher IS rating (5 vs. 4). The III has electronic manual focusing. While still available, the II's price is an advantage it holds.
The two closest Canon prime lens alternatives in the same price and quality category as the 600 L IS III are the Canon EF 500mm f/4.0L IS II USM Lens and Canon EF 800mm f/5.6L IS USM Lens. As of review time, testing these two super-telephoto lenses on the ultra-high-resolution 5Ds R is on the to-do list, so we need to visualize the image sharpness differences.
In the 600mm vs 500mm image quality comparison, it looks like the 500 might have a very slight advantage though the difference is hard to discern. Looking at the specs and measurements, the Canon EF 600mm f/4L IS III USM Lens vs. Canon EF 500mm f/4.0L IS II USM Lens comparison shows the 600mm weighing slightly less (push your jaw back up) but measuring more. The 600 has electronic manual focusing and a 1-stop-higher-rated IS system (5 vs. 4). The 500 costs considerably less and its 500mm focal length is noticeably less than the 600's.
The 800 L IS has a longer native focal length that is better for reaching small birds and similar targets, but it has a one stop narrower aperture. Since the 600 L II IS with a 1.4x extender mounted results in an 840mm f/5.6 lens, this becomes a highly-relevant comparison. In the image quality comparison, the 800 seems to have an advantage. That the 600 can be used without the 1.4x extender mounted is a big advantage it holds.
Looking at the specs and measurements, the Canon EF 600mm f/4L IS III USM Lens vs. Canon EF 800mm f/5.6L IS USM Lens comparison shows the 600 weighing far less and the 800 being a thinner lens. The 600 has electronic manual focusing and a 1-stop-higher-rated IS system (5 vs. 4). These two lenses share the same price without the extender cost factored in.
If we can add a 1.4x extender to the 600 to create a comparison, we can add the 1.4x to the Canon EF 400mm f/2.8L IS III USM Lens to create a comparable 560mm f/4 lens. In the image quality comparison, we see these two lenses performing very similarly. That the 400 can be used without the 1.4x extender mounted is a big advantage it holds.
Looking at the specs and measurements, the Canon EF 600mm f/4L IS III USM Lens vs. Canon EF 400mm f/2.8L IS III USM Lens comparison shows the 400 to be the considerably shorter lens. The 400 is slightly lighter (without the extender factored in) and slightly narrower. The 400 costs less with the extender taking a bite out of the difference.
The Canon EF 600mm f/4L IS III is a top-notch wildlife and sports lens created by a company with a long history of delivering best-available camera lenses. This lens is a roll-up of the best-available technology, including the technology utilized in the lens' design as well as the innovative manufacturing techniques required to make this lens a reality for the professionals who will ultimately rely on it.
This lens features superb build quality, a very long super-telephoto focal length, an ultra-wide aperture for that focal length, and a fast and precise AF system. The image quality is high-grade, though it falls slightly short of the bar set by the version II lens.
The built-for-speed EF 600mm f/4L IS III package works exceedingly-well for serious, discerning sports photographers, wildlife photographers, and photojournalists. This is the type of lens that will have under-funded photographers digging through their gear kits searching for anything that might be considered non-essential and potentially contributing to the 600mm f/4L IS III fund. Once the investment challenge has been overcome, taking delivery of a new Canon super-telephoto lens such as this one will make even the most jaded photographer feel like a kid on Christmas morning.
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