Canon RF 10-20mm F4 L IS STM Lens Review

Canon RF 10-20mm F4 L IS STM Lens

The Canon RF 10-20mm F4 L IS STM Lens includes the widest focal length in a full-frame zoom lens, and 10mm is crazy-wide. Having access to this zoom range facilitates creativity and enables imagery that is differentiating, standing out from the mundane. Professional and serious amateur photographers who want the extreme wide-angle advantage want this lens in their kits.

  • 10mm is awesome, dramatic, fun, differentiating
  • Zooming to 20mm adds great utility
  • Sharp at f/4
  • Professional grade
  • Quiet optical image stabilization
  • Lens function buttons
  • Fast, quiet, and smooth STM AF
  • Parfocal-like performance
  • Compact and lightweight
  • Fixed size
  • Expensive
  • Strong wide end barrel distortion requires correction
  • Strong peripheral shading at 10mm
  • Low maximum magnification
  • Front filters not supported
In-Depth Review

I am pleased to introduce you to the benchmark for wide: the Canon RF 10-20mm F4 L IS STM Lens includes the widest focal length in a full-frame zoom lens.

While most photographers will not leave a 10-20mm full-frame lens mounted on their primary camera 100% of the time, having access to that range is differentiating, facilitating creativity, and permitting problem-solving not previously available in-camera. Ultimately, this lens enables imagery that stands out from the mundane.

During the introduction of the RF mount, Canon's engineers shared with me that all RF lenses would have advantages over their EF lens counterparts with, minimally, equal and often improved image quality. Despite that promise, I can't say that I was prepared for this lens.

The comparable EF lens in this case is the Canon EF 11-24mm f/4L USM Lens, a previous holder of the same record. This lens is an outstanding performer, with excellent image quality at the top of its favorite advantages list.

Canon RF 10-20mm F4 L IS STM Lens Compared to EF 11-24mm f/4L USM Lens

In addition to widening the already-crazy-wide focal length by 1mm (the difference between 10mm and 11mm is huge) and adding a 5-stop optical image stabilization system that supports coordinated IBIS for 6-stops of assistance, the Canon RF 10-20mm F4 L IS STM Lens lost over 1/2 of the predecessor's weight and a similar amount of its size, even without the EF to R adapter factored in.

The RF mount's wide diameter combined with the short distance to the imaging sensor enabled the size of the front optical section to be dramatically reduced. Especially when this lens is serving secondary purposes, the smaller size and weight make taking it along a much easier proposition.

Wait, there's more. Perhaps the RF 10-20mm's biggest surprise is the significantly lower price. We didn't see that aspect coming.

Professional and serious amateur photographers who want stand-out imagery and can make use of ultra-wide angles will want the Canon RF 10-20mm F4 L IS STM Lens in their kits.

Canon RF 10-20mm F4 L IS STM Lens Top

Focal Length Range

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Focal length range (or individual focal length for a prime lens) is a primary consideration for lens selection. A specific angle of view is required to get a desired subject framing with the optimal perspective (or from within a working distance limitation).

While 20mm is in the ultra-wide class, 10mm is insanely wide-angle. The only wider-angle full-frame zoom lens is the Canon EF 8-15mm fisheye lens. However, the fisheye lens delivers an extremely barrel-distorted image, with straight lines rendered strongly curved (unless they pass directly through the center of the frame). Wider APS-C format lenses are available, but the angle of view provided in their reduced-size image circle is considerably narrower.

Let's jump right into a focal length comparison illustrating the 10-20mm focal length range.

Canon RF 10-20mm F4 L IS STM Lens Focal Length Range Example

10mm | 11mm | 12mm | 14mm | 16mm | 18mm | 20mm
10mm | 11mm | 12mm | 14mm | 16mm | 18mm | 20mm

Consider how wide your widest focal length is in relation to those availed by this lens. The difference between 10mm and 11mm is big, and the difference between 10mm and 12mm is huge.

What about the 15mm fisheye angle of view? How does it compare to rectilinear 10mm and other focal lengths?

15mm Fisheye Focal Length Compared to Rectilinear Focal Lengths

15mm | 10mm | 12mm | 14mm | 16mm | 18mm | 21mm | 24mm

The subject in the center of a 15mm fisheye image circle is magnified about the same as in a 15mm rectilinear frame. The fisheye lens's magnification decreases dramatically by the periphery, where details are considerably smaller than even those in a 10mm rectilinear lens frame. Note that the fisheye lens does not stretch corner details as the rectilinear options do.

While wider is great, we must also consider that the useful 21-24mm focal lengths have been omitted from the updated RF design vs. the EF lens.

20mm vs. 24mm Focal Length Example

You might want to wear scene-complementing shoes when using this lens because at 10mm, you might find it challenging to keep your feet (and your tripod's feet) out of the frame.

What uses are optimal for a 10-20mm lens? With the incredible popularity of photography today, it has never been harder to create work that stands out from the crowd, work that sets you apart or above (I said that many years ago). This lens can do that. The 10-20mm focal length range is useful for creating dramatic, exciting, and powerful imagery that differentiates your work.

A specific use that welcomes the 10-20mm range is landscape photography, especially for landscape scenarios that provide an interesting foreground rendered prominently in front of the big background.

As you likely noticed, the bulbous front lens element precludes the use of standard threaded front filters especially valued for landscape photography. I miss access to circular polarizer and neutral density filters when photographing waterfalls and mid-day landscapes when using such a lens. Watch for companies such as Fotodiox to implement a filter solution for this lens, but the filter holder and the filters themselves will be big, and it is quite likely that the widest angles will not be supported. Regardless, there remains a lot of landscape photography to be done without filters, and, as usual for wide-angle Canon lenses not accepting front filters, a slip-in rear gel filter holder is provided.

Architecture and real estate photographers will find this lens indispensable for outdoor and especially interior work. As illustrated above, this is a great ceiling lens. This is a full nightscape angle of view range, and with the low magnification at 10mm permitting a long exposure without star trails, an f/4 lens can even be a good choice for nightscapes.

People are a great subject for the 10-22mm angle of views if they are not too close to the camera (for perspective reasons). Use this lens to create outstanding environmentals.


Perhaps the "outstanding" designation does not apply to this Environmental Portrait, a selfie, but this 12mm image illustrates the concept.

Other 10-20mm lens uses include photojournalism, weddings, news, documentary, travel, commercial, and video. This car photo was captured with the RF 10-20 set to 16mm.

Canon RF 10-20mm F4 L IS STM Lens Car Sample Picture

Here is an 11mm sample photo from the predecessor lens showing the close words in concrete emphasized.

Canon EF 11-24mm f/4L USM Lens 11mm Sample Picture

This 10-20mm lens is a great option for mounting to a remote sports camera, capturing the start of a race, capturing the finish of a race, covering the goal, mounted over the basket, etc. The lens will also capture the big image of the venue.

While the RF 10-20mm lens is compatible with Canon's R series APS-C camera models, the smaller image circle makes this focal length range not so differentiating. Still, these cameras can fully utilize the image quality this lens delivers, and the 16-32mm full-frame angle of view fills an important role in the kit, covering similar needs and better covering wide portraiture.

Canon RF 10-20mm F4 L IS STM Lens Front

Max Aperture

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How much light does the lens provide to the imaging sensor? Usually, that question is the second most important when selecting a lens.

This lens opens to f/4 over the entire focal length range. This opening is modestly wide relative to that of other lenses but physically narrow to accommodate that spec for the short 10-20mm focal lengths.

Motion blur is caused by subject details crossing over imaging sensor pixels during the exposure. Although this lens can be used with a close subject rendered large in the frame, ultra-wide-angle focal lengths are often used at normal (or even long) subject distances. The low magnification means those subjects' details more readily stay in their pixels, enabling the longer exposures required to compensate for the narrower aperture to still deliver sharp results, free of subject or camera motion blur. F/4 is not an especially wide aperture, but in conjunction with the low magnification of a 10-20mm focal length range, it is sufficient for most needs, including action photography. F/2.8 would make this lens a better option for nightscapes and sports action, but f/4 still handles that role.

Many uses for this lens require a narrow aperture, such as f/8 or f/11, to keep everything in the frame sharp, and photographers concentrating on landscape, architecture, real estate, etc., may seldom use the f/4 option.

A smaller aperture opening facilitates using smaller, lighter, and less expensive lens elements, and the Canon RF 10-20mm F4 L IS STM Lens makes strong use of those first two attributes.

If diffusely blurring the background is your goal, the low magnification of an ultra-wide-angle lens is not the right solution. These examples illustrate the maximum blur this lens can create:

Canon RF 10-20mm F4 L IS STM Lens Maximum Blur Example

With a close subject, the background blur at 20mm is significant enough to make an in-focus subject stand out (or to simply create an artistic blur, which can be useful for backgrounds in ads, PowerPoint presentations, etc.).

Canon RF 10-20mm F4 L IS STM Lens Right Angle

Image Stabilization

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While the low magnification of the 10-20mm range may not scream the need for image stabilization, steadiness can be an image quality factor. This lens has a new high-performing IS system that increases its versatility and offsets the need for a wider aperture for still-subject image capture, including minimized wide-angle "fluttering" at the outer areas of the frame.

When the subject is not moving or not moving much, this lens's image stabilization system, rated for 5 stops of assistance, can make a huge difference in handheld image quality. Use this lens on an EOS R-series camera featuring In-Body Image Stabilization (IBIS), and that rating jumps to an even more significant 6.0 stops. RF mount communication between the lens and the camera makes these impressive ratings possible, and the 6.0 stop ISO noise difference referenced by this rating is dramatic.

I never achieve IS assistance ratings, but IS makes a huge difference in my image quality.

IS is useful for stabilizing the viewfinder, aiding in optimal composition, and it is useful for stabilizing movie recording. Don't overlook the stabilized image aid to AF precision.

This image stabilization system performs superbly, with sharp 1-second exposures indoors at 20mm seeming common. IS operates nearly silently, and it is well-behaved, meaning that the viewfinder image does not jump, and I do not find myself fighting against this IS system while recomposing, tracking fast action, or moving while recording video.

Canon RF 10-20mm F4 L IS STM Lens Side Angle

Image Quality

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Canon set the RF 10-20mm F4 L IS STM Lens image quality expectation high, indicating that the new lens was optically at least as good as its predecessor, a high-performing lens itself.

Here are the Canon RF 10-20mm F4 L IS STM Lens's MTF charts along with the Canon EF 11-24mm f/4L USM Lens charts for comparison.

Canon RF 10-20mm F4 L IS STM Lens MTF Chart Comparison

The black lines indicate contrast, and the blue lines show resolution. The solid lines are sagittal, and the dashed lines are meridional. The higher, the better, and the RF 10-20mm lens's lines are mostly similar to or higher than the EF 11-24's lines.

Note that the standard image quality test images for this lens, along with the comparisons featured below, are geometric distortion corrected unless otherwise noted, as forced by Canon Digital Photo Professional (DPP). More information on this regard is included in the distortion discussion below.

With the lens in the lab, the real-world performance can be assessed, and this lens is sharp in the center of the frame with a wide-open aperture. Little improvement is realized at narrower apertures, and no improvement is needed.

In the periphery of the image circle, where light rays are refracted to a stronger angle than in the center, lenses typically show decreased sharpness, and at 10mm f/4, this one shows a gradual decline from the center to the corner. Still, the 10mm f/4 corners are relatively sharp. As the focal length increases (and the geometric distortion correction is lessened), corner image quality improves, and 14mm through 20mm f/4 corners are sharp.

As with the center of the frame performance, stopping down brings little sharpness improvement to the periphery, aside from reduced peripheral shading.

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

Canon RF 10-20mm F4 L IS STM Lens Sharpness Comparison Example

10mm: f/4.0 | f/4.0 | f/4.0 | f/4.0 | f/4.0
15mm: f/4.0 | f/4.0 | f/4.0 | f/4.0 | f/4.0
20mm: f/4.0 | f/4.0 | f/4.0 | f/4.0 | f/4.0

The wide-open aperture images tell most of the center-of-the-frame story (they look great), and the minor change at f/5.6 didn't seem worth your bandwidth.

Next, we'll look at a series of comparisons showing 100% resolution extreme top left corner crops (the last pair of 10mm and 20mm crops are from the bottom left) captured and processed identically to the above center-of-the-frame images. The lens was manually focused in the corner of the frame to capture these images.

Canon RF 10-20mm F4 L IS STM Lens Corner Sharpness Comparison Example

10mm: 4.0 | 5.6   4.0 | 5.6   4.0 | 5.6   4.0 | 5.6
15mm: 4.0 | 5.6   4.0 | 5.6   4.0 | 5.6   4.0 | 5.6
20mm: 4.0 | 5.6   4.0 | 5.6   4.0 | 5.6

Samples taken from the outer extreme of the image circle, full-frame corners, can be counted on to show a lens's weakest performance. The results at 10mm show a bit of deep corner softness that improves nicely through 20mm.

This lens does not exhibit focus shift, the plane of sharp focus moving forward or backward as the aperture is narrowed (residual spherical aberration or RSA).

A lens is expected to show peripheral shading at its widest aperture settings when used on a camera that utilizes its entire image circle. At 10mm f/4, this lens's corners are darkened by about 4 stops, a significant amount.

The shading linearly decreases with focal length increase until about 2.5 stops remain at 20mm. That amount is not bad for wide-open at this focal length.

At f/5.6, 10mm corners gain a stop of brightness, and the other focal lengths gain about half a stop. The corners brighten only slightly at f/8 and through f/16.

APS-C format cameras using lenses projecting a full-frame-sized image circle avoid most vignetting problems. In this case, the about one-stop of corner shading showing at f/4 may be visible in select images, primarily those with a solid color (such as a blue sky) in the corners.

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

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

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

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

Canon RF 10-20mm F4 L IS STM Lens Lateral Chromatic Aberration Example

10mm | 12mm | 14mm | 16mm | 18mm | 20mm

Only black and white colors should be present in these images, with the additional colors indicating the presence of lateral CA. A moderate amount of color separation shows at 10mm, slowly resolving until a minor amount remains in the 20mm results.

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

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

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

Canon RF 10-20mm F4 L IS STM Lens Spherical and Axial Aberration Example

10mm | 15mm | 20mm

These results look great.

Bright light reflecting off lens elements' surfaces may cause flare and ghosting, resulting in reduced contrast and sometimes interesting, usually destructive visual artifacts. The shape, intensity, and position of the flare and ghosting effects in an image are variable, dependent on the position and nature of the light source (or sources), selected aperture, shape of the aperture blades, and quantity and quality of the lens elements and their coatings. Additionally, flare and ghosting can impact AF performance.

This lens features Canon's SSC (Super Spectra Coating), SWC (Subwavelength structure coating), and ASC (Air Sphere Coating), an ultra-low refractive index coating consisting of air and silicon dioxide, to combat flare and ghosting.

It is easy to get the sun in the frame at focal lengths this wide. Fortunately, this lens produced practically no flare effects even at narrow apertures in our standard sun in the corner of the frame flare test, reflecting excellent performance.

Flare effects can be embraced or avoided, or removal can be attempted. Unfortunately, removal is sometimes challenging, and in some cases, flare effects can destroy image quality. Thus, high flare resistance is a welcomed trait of this lens.

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

The images below are 100% crops taken from the top-left corner of EOS R5 images captured at the widest available aperture.

Canon RF 10-20mm F4 L IS STM Lens Coma Example

10mm | 15mm | 20mm

From a relative standpoint, these results are good.

This lens has dramatic barrel distortion at the wide end. The geometric distortion is strong enough that Canon forces the correction in camera (EVF, LCD, JPG images, movies) and in DPP, regardless of the lens corrections settings selected. Processing the distortion test images for this lens with third-party software results in off-the-chart framing that shows the true image captured.

For reference, the squares in the test chart filled the viewfinder during capture. At 10mm, there is a lot of extra subject in the frame, and the straight line between the squares at the top of the chart is rendered as a strong curve.

As the focal length increases, the barrel distortion improves until only modest at 20mm. Still, Canon corrects the 20mm results.

Every lens is a compromise, with size, weight, price, image quality, and focal length range being common factors, and with increasing frequency, manufacturers are relying on software over physical lens design to manage geometric distortion. While severe distortion and the required crop factor (or stretching) is a detriment to this lens, the offsetting factors are welcomed. Still, the distortion amount must be considered when comparing lenses, and an image captured from a non-distorted lens can be similarly up sized to even higher resolution using the same AI, potentially giving it an advantage.

Here is a 10mm uncorrected and corrected distortion comparison.

Canon RF 10-20mm F4 L IS STM Lens Geometric Distortion Example

As seen earlier in the review, it is easy to illustrate the strongest blur a lens can create, and wide-angle lenses are inherently disadvantaged in this regard. Here are some f/11 (for diaphragm blade interaction) 100% crop examples.

Canon RF 10-20mm F4 L IS STM Lens Bokeh Example

10mm | 15mm | 20mm   10mm | 20mm

These are not the prettiest results, but they are as expected for the focal lengths.

Except for a small number of specialty lenses, the wide aperture bokeh in the frame's corner does not produce round defocused highlights, with these effects taking on a cat's eye shape due to a form of mechanical vignetting. If you look through a tube at an angle, similar to the light reaching the frame's corner, the shape is not round. That is the shape we're looking at here. The following images are crops of the upper-left 1/3 corner.

Canon RF 10-20mm F4 L IS STM Lens Cat's Eye Bokeh Example

10mm | 15mm | 20mm

While the corner shapes are not circular, they are not bad.

A 9-blade count diaphragm will create 18-point sunstars (diffraction spikes) from point light sources captured with a narrow aperture. Generally, the more a lens diaphragm is stopped down, the larger and better shaped the sunstars tend to be. Medium-wide aperture lenses tend to create medium-quality stars, but, as illustrated below, this lens's stars are nicely shaped, though small.

Canon RF 10-20mm F4 L IS STM Lens Sunstar Effect Example

The examples above were captured at f/16.

Canon RF 10-20mm F4 L IS STM Lens Design

This lens's complex optical design, illustrated above, includes 1 super UD lens, 3 UD lenses, and 3 aspheric lenses.

The strong barrel distortion is easily this lens's biggest weakness, but overall, it produces the high-end image quality expected from a member of the RF L-series.

Canon RF 10-20mm F4 L IS STM Lens on Tripod


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Wait. An STM-powered AF system in a Canon L series lens? This stepping motor is fast, quiet, smooth, and precise.

As usual, low light AF is slowed, but this f/4 lens will still lock focus on a contrasty subject in dark environments.

Usually, non-cinema lenses require refocusing after a focal length change. As illustrated in the 100% crops below, the reviewed lens does exhibit parfocal-like characteristics. When focused at 20mm, subjects remain in focus when zooming to wider focal lengths.

Canon RF 10-20mm F4 L IS STM Lens Parfocal Example

20mm | 18mm | 16mm | 14mm | 12mm | 10mm

Especially videographers will appreciate this performance.

Canon RF 10-20mm F4 L IS STM Lens Side

A Lens Function button is provided at a position most convenient for horizontally oriented camera use. By default, the button provides the AF stop function, locking focus at the currently selected distance, permitting a focus and recompose technique. However, it can be programmed for numerous other functions.

Here is a partial list of functions assignable to the Lens Function buttons:

  • AF Stop (default)
  • Metering/AF start
  • Switch to saved AF function
  • One-Shot AF / Servo AF
  • Eye detection
  • Switch to saved AF frame
  • AE lock
  • AE lock (hold)
  • Exposure compensation (turn main electronic dial while button is depressed)
  • Activate IS function
  • Aperture
  • Many more ...

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

That this lens has an AF/MF switch is a positive attribute, allowing this frequently used camera setting to be changed without accessing the menu system.

Canon RF 10-20mm F4 L IS STM Lens Switches

The ribbed-rubber, modestly sized focus ring is positioned in front of the zoom ring as I prefer. However, the limited amount of space on the lens barrel means that finding this ring between the zoom ring and the control ring requires a bit of concentration.

The focus ring is extremely smooth and ideally damped. With the camera's RF lens MF focus ring sensitivity menu option set to "Varies with rotation speed", a slow 280° adjusts from MFD to infinity at 10mm and 180° does the same at 20mm. The numbers are about 130° and 110° for a fast turn.

It is normal for the scene to change size in the frame (sometimes significantly) as the focus is pulled from one extent to the other. This effect is focus breathing, a change in focal length resulting from a change in focus distance. Focus breathing impacts photographers intending to use focus stacking techniques, videographers pulling focus (without movement to camouflage the effect), and anyone critically framing while adjusting focus.

This lens produces a moderate change in subject size through a full-extent (worst-case) focus distance adjustment.

Canon RF 10-20mm F4 L IS STM Lens Focus Magnification Example

10mm: Far | Close   20mm: Far | Close   10mm: Far | Close

As seen in the second set of 10mm results, the focus breathing affects mechanical vignetting at the wide end. The camera or software corrects for this shading.

The EF 11-24mm Lens has a relatively low maximum magnification spec (0.16x), but with a shorter long end, the RF 10-20 generates a modestly lower 0.12x maximum magnification spec, despite having a shorter minimum focus distance (9.8", 250mm).

ModelMin Focus Distance "(mm)Max Magnification
Canon EF 8-15mm f/4L USM Fisheye Lens5.9(150)0.39x
Canon RF 10-20mm F4 L IS STM Lens9.8(250)0.12x
Canon EF 11-24mm f/4L USM Lens11.0(280)0.16x
Canon RF 14-35mm F4 L IS USM Lens7.9(200)0.38x
Canon RF 15-35mm F2.8 L IS USM Lens11.0(280)0.21x
Sigma 14-24mm f/2.8 DG DN Art Lens11.0(280)0.14x
Sony FE 12-24mm F2.8 GM Lens11.0(280)0.14x
Sony FE 12-24mm F4 G Lens11.0(280)0.14x

At 10mm, a subject measuring approximately 20.5 x 13.7" (520 × 347mm) fills a full-frame imaging sensor at this lens's minimum MF distance. At 20mm, an 11.2 x 7.4" (284 x 189mm) subject does the same.

Canon RF 10-20mm F4 L IS STM Lens Focus Magnification Example

The USPS love stamps shared above have an image area that measures 1.05 x 0.77" (26.67 x 19.558mm), and the overall individual stamp size is 1.19 x 0.91" (30.226 x 23.114mm).

At minimum focus distance at 20mm, this lens produces good image quality, including the corners still looking good.

Here is a 20mm flower example.

Canon RF 10-20mm F4 L IS STM Lens Focus Magnification Flower Example

This lens is not compatible with Canon extenders.

Canon RF 10-20mm F4 L IS STM Lens Front on Camera

Design & Features

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As a Canon flagship L series lens, the RF 10-20mm F4 L IS STM Lens is built for professional durability requirements. While this build quality is crucial to professionals, a huge number of serious amateurs also recognize this importance.

With smooth external dimensions and tight tolerance between parts, the Canon RF 10-20mm F4 L IS STM Lens is comfortable to hold, and it is a pleasure to use.

Canon RF 10-20mm F4 L IS STM Lens Product Images

MFD |    MFD |    Rotated   Compare »

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

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

This lens features a quality plastic external construction. While the overall size of this lens does not change with focal length, the front element moves within the hood.

Canon RF 10-20mm F4 L IS STM Lens Zoom Extension

The AF/MF and IS switches are flush-mounted and low-profile, with just enough raised surface area available for easy use, even with gloves. These switches snap crisply into place.

Canon RF 10-20mm F4 L IS STM Lens Mount

This lens design features dust and moisture resistance, a feature especially valuable in the field.

Canon RF 10-20mm F4 L IS STM Lens Weather Sealing

The front lens element features a fluorine coating that repels fingerprints, dust, water, oil, and other contaminants and makes cleaning considerably easier.

The EF 11-24mm lens's front section was wide, requiring a substantial amount of space in the case. That lens was also heavy.

As discussed at the beginning of this review, the RF 10-20mm lens is dramatically smaller and lighter. This lens's size and weight make it comfortable to carry and use even during extended sessions.

ModelWeight oz(g)Dimensions w/o Hood "(mm)FilterYear 
Canon EF 8-15mm f/4L USM Fisheye Lens19.1(540)3.1 x 3.3(78.5 x 83.0) 2010
Canon RF 10-20mm F4 L IS STM Lens20.1(570)3.3 x 4.4(83.7 x 112.0) 2023
Canon EF 11-24mm f/4L USM Lens41.7(1180)4.3 x 5.2(108.0 x 132.0) 2015
Canon RF 14-35mm F4 L IS USM Lens19.1(540)3.3 x 3.9(84.1 x 99.8)772021
Canon RF 15-35mm F2.8 L IS USM Lens29.7(840)3.5 x 5.0(88.5 x 126.8)822019
Sigma 14-24mm f/2.8 DG DN Art Lens28.1(795)3.3 x 5.2(85.0 x 131.0) 2020
Sony FE 12-24mm F2.8 GM Lens29.9(847)3.8 x 5.4(97.6 x 137.0) 2020
Sony FE 12-24mm F4 G Lens19.9(565)3.4 x 4.6(87.0 x 117.4) 2017

For many more comparisons, review the complete Canon RF 10-20mm F4 L IS STM Lens Specifications using the site's lens specifications tool.

Here is a visual comparison:

Canon RF 10-20mm F4 L IS STM Lens Compared to Similar Lenses

Positioned above from left to right are the following lenses:

Canon RF 14-35mm F4 L IS USM Lens
Canon RF 10-20mm F4 L IS STM Lens
Canon RF 15-35mm F2.8 L IS USM Lens
Sony FE 12-24mm F2.8 GM Lens

Use the site's product image comparison tool to visually compare the Canon RF 10-20mm F4 L IS STM Lens to other lenses.

As indicated in the chart above, there is no provision for the Canon RF 10-20mm F4 L IS STM Lens to accept front filters. Circular polarizer filters are not supported, but gel filters can be cut to fit into the slot on the lens mount. Neutral density filters are a frequently used gel filter option, though finding a fully-color-neutral gel filter may be problematic.

The lens hood is integrated.

Canon RF 10-20mm F4 L IS STM Lens Case

A drawstring Canon Lens Pouch LP1219 is included in the box. While the bottom of this pouch is padded, the unpadded sides primarily protect against dust and scratches vs. impact.

Canon RF 10-20mm F4 L IS STM Lens Cap

A wrap-around, clip-on cap protects the front of the lens when not in use.

Canon RF 10-20mm F4 L IS STM Lens Cap Back

While the cap attaches only with the releases on top and bottom, ridges inside the cap direct the installation orientation.

Canon RF 10-20mm F4 L IS STM Lens Angle

Price, Value, Compatibility

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Want a lens to appear as a great bargain? Make it a significant upgrade to the predecessor lens and give it a significantly lower price.

As an "RF" lens, the Canon RF 10-20mm F4 L IS STM Lens is compatible with all Canon EOS R-series cameras, including full-frame and APS-C models.

The reviewed Canon RF 10-20mm F4 L IS STM Lens was on loan from Canon USA.

Canon RF 10-20mm F4 L IS STM Lens Close Angle


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The easy choice for a lens alternative is the predecessor lens, and in this case, the high-performing Canon EF 11-24mm f/4L USM Lens is easily the closest option.

In the image quality comparison, the two lenses perform similarly with a wide-open aperture at their wider focal lengths, but the 10-20 is noticeably sharper in the periphery at 18mm and 20mm. The sharpness differences at f/5.6 are minimal. The 10-20 has less lateral CA at the wide end and shows significantly fewer flare effects. It has slightly less peripheral shading at the wide end and slightly more at the long end. The 11-24 has significantly less geometric distortion.

The Canon RF 10-20mm F4 L IS STM Lens vs. EF 11-24mm f/4L USM Lens comparison shows the 10-20 weighing less than half as much as the 11-24, and the size difference is also dramatic. The 11-24 requires the Canon Mount Adapter EF-EOS R for use on an EOS R-series camera, which increases these differences. The 10-20 has image stabilization and an STM AF system vs. Ring USM. The 11-24 has a higher maximum magnification (0.16x vs. 0.12x) and a dramatically higher price. The focal length differences are significant on both ends.

The Canon RF lens with the closest focal length range is the Canon RF 14-35mm F4 L IS USM Lens. This angle of view coverage difference is significant, but there is some overlap.

The image quality comparison shows the two lenses performing similarly. The 14-35 has modestly more lateral CA at 14mm and considerably stronger barrel distortion at 14mm.

The Canon RF 10-20mm F4 L IS STM Lens vs. RF 14-35mm F4 L IS USM Lens comparison shows the two lenses weighing about the same, with the 14-35 measuring longer. The 14-35 externally extends with zooming, accepts 77mm threaded filters, and has a removable hood. The 14-35 has Nano USM vs. STM and features 0.38x maximum magnification vs. 0.12x. The 10-22 costs significantly more that the 14-35.

Crossing over to the Sony system, we have the outstanding FE 12-24mm F2.8 GM Lens.

Again, the focal length differences are significant, especially on the wide end, but the max aperture difference is also big.

The image quality comparison shows the two lenses performing similarly at their widest apertures. Equalizing the apertures at f/4 gives the Sony lens an advantage. Even with a wide-open aperture, the Sony lens has less peripheral shading, and significantly less at f/4 and f/5.6. The Sony lens has dramatically less geometric distortion.

The Canon RF 10-20mm F4 L IS STM Lens vs. Sony FE 12-24mm F2.8 GM Lens comparison shows the Sony lens weighing 50% more with significantly longer measurements. The Sony lens has a slightly higher maximum magnification spec, 0.14x vs. 0.12x, and a considerably higher price.

Use the site's tools to create additional comparisons.


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The Canon RF 10-20mm F4 L IS STM Lens brings extraordinarily wide full-frame angles of view to Canon's mirrorless R series cameras. This lens holds the potential for creating dramatic, exciting, and powerful imagery that differentiates your work.

It is also extremely fun to use.

Canon RF 10-20mm F4 L IS STM Lens
Canon RF 10-20mm F4 L IS STM Lens
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