Canon RF 50mm F1.8 STM Lens Review

Want to create a best selling lens? Start with the highly popular, useful 50mm focal length and add a relatively wide f/1.8 aperture. With the compact size, light weight, and low price that combination avails, these models tend to live at or near the top of best-seller lists. That is where you can expect to find the Canon RF 50mm F1.8 STM Lens.

Focal Length

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Sometimes, it is easy to justify the purchase of a lens for a subset of its attributes (such as extreme sharpness). Still, when it is time to select the ideal lens for a particular use, the focal length always becomes a primary consideration. The focal length determines the angle of view, which determines the subject distance required for the desired framing, and the distance from the subject determines the perspective.

On a full-frame body, a 50mm focal length provides an angle of view that seems natural, and that aspect brings great general-purpose usefulness. So useful, and thus, so popular, is this focal length that 50mm (or similar) focal length prime lenses are found in all major brand lens lineups, with some having numerous options (Canon has six 50mm prime lenses at review time).

Fifty mm lenses are frequently used for fashion, portraiture, weddings, documentary, street, lifestyle, sports, architecture, landscape, commercial, around-the-home, and general studio photography applications, including product photography. As you likely noted, a number of good applications for this lens include people as subjects. While a 50mm lens used (on a full-frame body) has a modestly too wide angle of view for tightly framed headshot portraits (a too-close perspective is required), but it is great for wider portrait framing.

Having a 50mm focal length and f/1.8 aperture available opens many artistic opportunities, including those found in nature.

To visualize where 50mm fits among other common focal lengths, I'll borrow a focal length range example from the Canon EF 24-105mm f/3.5-5.6 IS STM Lens review.

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At review time, this lens is not compatible with any APS-C (1.6x FOVCF) format cameras. Should that scenario change in the future, or should an R-series cameras' 1.6 crop mode be used, the full-frame angle of view equivalent becomes 80mm. This angle of view works for similar subjects, with more working space required and tighter framed headshot portraits having better perspective.

Max Aperture

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The basics: the lower the aperture number, the more light the lens will allow to reach the sensor. Each "stop" in aperture change (examples: f/1.4, f/2, f/2.8, f/4.0) increases or reduces the amount of light reaching the sensor by a factor of 2x (a big deal).

A feature that many prime (fixed focal length) lenses have is an ultra-wide aperture. Among all lenses that avail the 50mm focal length, the f/1.8 aperture is wide, allowing a significant amount of light to reach the imaging sensor. This lens is a good choice for stopping motion, both subject and camera motion, in low light conditions, including those typically found indoors. The wide aperture also enables autofocusing in low light conditions.

Among 50mm prime lenses, f/1.8 is a somewhat narrow aperture, with f/1.4 being quite common and Canon's incredible Canon RF 50mm f/1.2 L USM Lens opening even wider. Having a narrower max aperture within the prime lens class results in this lens having a significantly smaller size, lighter weight, and considerably lower price.

Valuable is that increasing the opening permits a stronger, better subject-isolating background blur (at equivalent focal lengths) via shallower depth of field. Here is an example created with the similarly spec'd Canon EF 50mm f/1.8 STM Lens on a full-frame camera:

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The depth of field continues to increase as the aperture narrows beyond f/8, but the change is not noticeable at this resolution.

This is the maximum background blur this lens can produce:

There is a nice amount of blur seen in this example.

Image Stabilization

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There are still no 50mm image-stabilized lenses in Canon's RF lens lineup. With the wide aperture, this lens has less need for image stabilization. Image stabilization has costs, including size, weight, and price. In addition, Canon's latest R-series cameras feature IBIS (In Body Image Stabilization) with up to 7 stops of shake correction, significantly improving handheld image sharpness when the exposure durations begin to lengthen.

Image Quality

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Most 50mm prime lenses (the Canon RF 50mm f/1.2 L USM Lens outstanding) are not so sharp at their widest aperture setting. Would the second RF 50mm lens also break the mold?

In the center of the frame, with a wide-open aperture, the RF 50 f/1.8 is slightly soft. If this lens was priced at $2,000, I would be disappointed. At this price point, expectations are met or perhaps even exceeded slightly. F/1.8 imagery is quite usable, especially with some mild additional contrast and sharpening applied. By f/2.8, center of the frame results are quite sharp.

Image quality typically degrades as the image circle's radius is traversed, meaning that corners are seldom rendered as crisply as the center of the frame. That is the scenario we find here. The corners are blurry at f/1.8. Very slow improvement is seen as the aperture is narrowed, with reasonably sharp corners being rendered at f/11.

The following is 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). Note that images from most cameras require some level of sharpening, but too-high sharpness settings are destructive to image details and hide the deficiencies of a lens.

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The aberrations noticeably clear, and the contrast significantly increases by f/2.8, as is quite common for lenses in this class.

In some lens designs, the plane of sharp focus can move forward or backward as a narrower aperture is selected. This effect is called focus shift (residual spherical aberration or RSA), and it is undesired. The following is a study of this effect at a relatively close focus distance. Note the depth of field being primarily increased behind the initial (f/1.8) plane of sharp focus, especially at the wider apertures.

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

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Samples taken from the outer extreme of the image circle, full-frame corners in this case, can be counted on to show the worst performance a lens is capable of, and the f/1.8 results are among the blurriest I've seen from a recent Canon lens. Improvement comes on slowly as this lens is stopped down. The softening effects of diffraction cause the f/11 results to go in the other direction.

Corner sharpness does not always matter. When I'm photographing landscapes and architecture with corner sharpness being desired, I'm probably using f/8 or f/11 to obtain enough depth of field for in-focus corner details, and this lens works sufficiently for this purpose at these apertures. When shooting at wide apertures, the corners are most often out of focus and not supposed to be sharp. Videos captured at typical wide-aspect ratios also avoid the use of corners.

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 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 not to have the problem in the first place. Here is a look at a worst-case example, a 100% crop from the extreme top left corner of an ultra-high resolution EOS R5 frame showing diagonal black and white lines.

There should only be black and white colors in this image, and that is primarily what I see. This lens performs nicely in this regard.

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 observe. Axial CA remains at least 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.

In the examples below, look at the fringing colors in the out of focus specular highlights. Created by the neutrally-colored subjects, fringing color differences were introduced by the lens.

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There is a strong color separation showing at the wider apertures. This effect can also be seen in the focus shift example shared earlier in the review. Expect these colors to be present in images.

Flare and ghosting are caused by bright light reflecting off the surfaces of lens elements, resulting in reduced contrast and sometimes-interesting but often destructive artifacts. With only 6 lens elements (in 5 groups), the RF 50 F1.8 shows few flare effects in our standard sun in the corner of the frame testing. However, move the sun to a different location out of the frame and watch for Revelation-grade God rays.

Flare effects can be embraced or avoided, or removal can be attempted. Removal is sometimes challenging. I don’t recall seeing a stronger flare than the just-shared example.

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

The image below is a 100% crop taken from the top-left corner of an EOS R5 frame.

After seeing the corner sharpness results from this lens, you are likely not surprised to see this lens performing poorly in this test.

Geometric distortion is not an issue with this lens. Expect your straight lines to be rendered straight.

As seen earlier in the review, the amount of blur a lens can produce is easy to show, and standard lenses are middling performers in this regard. Assessing the quality is more challenging due in part to the infinite number of variables present among all available scenes. Here are two f/80 (for aperture blade interaction) examples.

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The first set of examples show defocused highlights. Seven aperture blades stopped down significantly result in squared-off borders, but the shapes are nicely filled. The second result shows a full-frame reduced in size. This sample appears fine.

Except for a small number of specialty lenses, the wide aperture bokeh in the corner of the frame 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 corner of the frame, the shape is not round. That is the shape seen here.

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The widest aperture results show out-of-round specular highlights in the periphery, but the shapes are not strong. As the aperture narrows, the entrance pupil size is reduced, and the mechanical vignetting absolves with the shapes becoming rounder.

With a 7-blade count aperture, point light sources captured with a narrow aperture setting and showing a sunstar effect will have 14 points. In general, the more a lens is stopped down, the larger and better-shaped the sunstars tend to be. Wide aperture lenses tend to have an advantage in this regard, and this lens is capable of producing beautiful stars.

That example was captured at f/16.

Overall, the Canon RF 50mm F1.8 STM Lens is not a top performer from an image quality perspective. That the price tag is so low makes it easier to overlook the shortcomings, and especially when stopped down modestly, this lens can produce high-quality imagery.

Focusing

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The Canon RF 50mm F1.8 STM Lens features state of the art economical focusing technology. In other words, this lens gets the best AF system available for a low price.

The EOS R-series cameras are impressively accurate-focusing, and the RF 50mm f/1.8 STM Lens is not an exception on this camera.

The RF 50 F1.8 features a stepping motor (the "STM" in the name) driven AF system that is quite fast, with even long focus distance changes happening quickly. As usual, focusing in low light is slower, but this lens can focus in dark conditions. The RF 50mm f/1.8 will impressively focus on bright stars.

The focusing is relatively quiet, though some clicking is audible with a buzz heard during long focus distance changes. You can expect on-board audio recording to pick up these AF sounds. While the sound is deceptive from a smoothness perspective, the EOS R focuses this lens relatively smoothly (a benefit for video recording). Also, the aperture adjusts quietly and smoothly – it is ideally-suited for movie recording where lighting can change.

This lens uses a front-focusing design, extending the front lens elements as the focus distance decreases.

The RF 50mm f/1.8's knurled plastic focus ring is relatively small but quite usable. The ring turns smoothly with a long 360° of rotation between focus extents. The rate of focus change is linear – not variable with rotation speed.

Manual focusing shows tiny steps of adjustment when viewed closely. Note that the spherical aberration discussion earlier in the review makes precise manual focus challenging.

The RF 50mm f/1.8 has a focus-by-wire or electrical manual focus system (vs. a direct gear-driven system) common for STM lenses. The manual focus ring electronically controls the focus of the lens. FTM (Full Time Manual) focusing is supported in AF mode with the camera in One Shot drive mode (if electronic manual focusing is enabled in the camera menu), but the shutter release must be half-pressed for the focus ring to become active. With MF selected in the camera's AF/MF menu, the camera meter must be on/awake for manual focusing to be available.

Big subject magnification/framing changes are seen in the long full extent focus range change this lens avails.

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A focus distance window is not provided, but a focus distance meter can be displayed in the lower portion of the camera's electronic viewfinder during manual focusing.

With a minimum focus distance of 11.8" (300mm), this lens has a 0.25x maximum magnification spec.

Model	Min Focus Distance "(mm)		Max Magnification
Canon RF 35mm F1.8 IS STM Macro Lens	6.7	(170)	0.50x
Canon RF 50mm F1.2 L USM Lens	15.7	(400)	0.19x
Canon EF 50mm f/1.2L USM Lens	17.7	(450)	0.15x
Canon EF 50mm f/1.4 USM Lens	17.7	(450)	0.15x
Canon RF 50mm F1.8 STM Lens	11.8	(300)	0.25x
Canon EF 50mm f/1.8 STM Lens	13.8	(350)	0.21x
Canon EF 50mm f/1.8 II Lens	17.7	(450)	0.15x
Canon TS-E 50mm f/2.8L Tilt-Shift Macro Lens	10.6	(270)	0.50x

A subject measuring approximately 5.4 x 3.6" (137 x 91mm) fills the frame of a full-frame camera at the minimum focus distance.

Magnification from standard focal length lenses is generally noticeably increased with the use of extension tubes, hollow tubes with electronic connections that shift a lens farther from the camera. This increased distance allows the lens to focus closer, though at the expense of long-distance focusing. As of review time, Canon does not offer RF mount-compatible extension tubes, but third-party options are available.

This lens is not compatible with Canon extenders.

Build Quality & Features

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The Canon RF 50mm F1.8 STM Lens is similar in style to the Canon RF 35mm f/1.8mm IS STM Macro Lens and Canon RF 85mm F2 Macro IS STM Lens.

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Front-focusing lens designs usually extend while focusing, with this lens reaching its maximum 0.53" (13.4mm) extension at minimum focus distance. Enable the "Retract lens on power off" setting in the camera menu to ensure that the lens is fully retracted after use. However, know that the lens will not retain its focus distance if the camera goes to sleep with that setting enabled.

Unusual behavior occurs when pushing the lens cap on while the lens is focused near infinity and the camera is on and awake. The lens retracts slightly under the light pressure while the AF motor attempts to push the lens barrel back out. Pushing against the motor cannot be good from a durability perspective, so be gentle with the cap installation.

Canon's metal RF mount is attractive and is nicely shaped for mounting and dismounting the lens. Utilizing engineering plastic construction, the RF 50mm f/1.8 lens's slightly-textured exterior barrel looks and feels nice, as does the straight exterior diameter of this design.

The RF 50 F1.8's knurled plastic ring is dual purposed, useful for manual focusing, and also as a control ring. This ring is configurable for fast access to camera settings, including aperture, ISO, and exposure compensation. Note that the control ring is unclicked.

The focus/control ring switch is flush-mounted with just enough raised surface area to be easily used, even with gloves. I'll mention again that switching between AF and MF requires selecting a menu option.

This lens is not weather-sealed nor fluorine coated on either end, increasing the chance of dust and moisture penetration and increasing the cleaning difficulty.

This is a small and light lens that takes up little space in the bag and requires little effort to carry and use. Those aspects increase the joy of use, with reduced fatigue increasing the photographer's sharpness — an image quality factor.

Model	Weight oz(g)		Dimensions w/o Hood "(mm)		Filter	Year
Canon RF 35mm F1.8 IS STM Macro Lens	10.8	(305)	2.9 x 2.5	(74.4 x 62.8)	52	2018
Canon RF 50mm F1.2 L USM Lens	33.5	(950)	3.5 x 4.3	(89.8 x 108.0)	77	2018
Canon EF 50mm f/1.2L USM Lens	19.2	(545)	3.4 x 2.6	(85.4 x 65.5)	72	2006
Canon EF 50mm f/1.4 USM Lens	10.2	(290)	2.9 x 2.0	(74.0 x 51.0)	58	1993
Canon RF 50mm F1.8 STM Lens	5.6	(160)	2.7 x 1.6	(69.2 x 40.5)	43	2020
Canon EF 50mm f/1.8 STM Lens	5.6	(159)	2.7 x 1.5	(69.2 x 39.3)	49	2015
Canon EF 50mm f/1.8 II Lens	4.6	(130)	2.7 x 1.6	(68.0 x 41.0)	52	1990
Canon TS-E 50mm f/2.8L Tilt-Shift Macro Lens	33.4	(945)	3.4 x 4.5	(86.9 x 114.9)	77	2017

For many more comparisons, review the complete Canon RF 50mm F1.8 STM Lens Specifications using the site's lens specifications tool.

A visual size comparison is always useful:

Positioned above from left to right are the following lenses:

Canon RF 35mm F1.8 IS STM Macro Lens
Canon RF 50mm F1.8 STM Lens
Canon RF 50mm F1.2 L USM Lens

Use the site's product image comparison tool to visually compare the Canon RF 50mm F1.8 STM Lens to other lenses.

Of the 472 lenses in our database, only three other lenses share the RF 50 F1.8's tiny 43mm filter thread diameter. All three are Canon EF-M Lenses. While 43mm filters are not common, they are small and inexpensive.

As with most Canon non-professional series lenses, the RF 50mm f/1.8 lens hood is optional. I highly recommend using lens hoods most of the time, primarily for the impact protection and light-shading properties they provide. However, Canon charges a significant amount for something with a low production cost that should be included in the box. The Canon ES-65B Lens Hood is a semi-rigid plastic round-shaped hood with a smooth, matte interior surface. This hood provides good protection from bright flare-inducing light and also from impact. A petal-shaped hood is easier to align for installation (simply learn the petal orientation — small petal to the top), while a rounded hood such as this one enables the lens to stand on its hood.

Also excluded from the RF 50mm f/1.8 lens box is a case. Lens cases are generally not expensive, and this one does not need a large model. Canon suggests their Lens Case LP1014, a drawstring pouch that adds dust and minor impact protection (the bottom is well-padded). Consider a Lowepro Lens Case or Think Tank Photo Lens Case Duo for a quality, affordable single-lens storage, transport, and carry solution.

Price, Value, Compatibility

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At its introduction, the Canon RF 50mm F1.8 STM Lens is by far the least expensive RF lens — half as expensive as the next-lowest-priced Canon RF lens. That fact alone makes it hard to argue that this lens is not a good value. Add reasonable image quality and great utility to the equation and the case is proven.

As an "RF" lens, the Canon RF 50mm f/1.8mm STM Lens is compatible with all Canon EOS R series cameras. Canon USA provides a 1-year limited warranty.

The reviewed Canon RF 50mm f/1.8mm STM Lens was online-retail sourced.

Alternatives

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The primary lens to be compared to the RF 50mm F1.8 is the Canon EF 50mm f/1.8 STM Lens. As seen above, these two lenses have a strong resemblance.

In the image quality comparison at f/1.8, the RF lens has a slight advantage, primarily in the image circle periphery. By f/2.8, the EF lens may be slightly sharper in the center of the frame, and the RF lens is slightly sharper deep in the corners. The EF lens has less peripheral shading, and the RF lens has less geometric distortion. Overall, the image quality difference between these lenses is only slight.

Looking at the specs and measurements, the Canon RF 50mm F1.8 STM Lens vs. Canon EF 50mm f/1.8 STM Lens comparison shows these lenses being nearly identical. The RF lens has 43mm filter threads vs. 49mm. The RF lens has a slightly shorter minimum focus distance for a higher maximum magnification spec (0.25x vs. 0.21x). Initially, the EF lens has a considerably lower price, but it requires an adapter to be used on a camera with an RF mount, adding significantly to the overall size and cost. If you have an RF mount camera, get the RF lens.

The Canon RF 50mm F1.2 L USM Lens is the focal length sharing option as of review time. This impressive lens is in a completely different class. If the size, weight, and price are acceptable, get it.

I'll pick the Canon RF 35mm F1.8 IS STM Macro Lens as the next best comparison lens. The 35mm focal length is noticeably different than the 50mm focal length, but a large overlap in uses exists.

In the image quality comparison, the 35mm lens appears to be modestly sharper, especially in the periphery. The RF 35 has modest barrel distortion.

Looking at the specs and measurements, the Canon RF 50mm F1.8 STM Lens vs. Canon RF 35mm F1.8 IS STM Macro Lens comparison shows the RF 35 weighing nearly twice as much (though still weighing little) and measuring noticeably longer (though still rather short). The RF 50 uses 43mm filters vs. 52mm. The RF 35 focuses much closer, able to generate a 0.50x maximum magnification vs. 0.25x. That the RF 35 is 2.5x more expensive than the RF 50 will be a decisive factor for many.

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

Summary

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While the Canon RF 50mm F1.8 STM Lens is not the highest performing lens from an image quality perspective, the image quality is decent (quite good stopped down), and this lens holds some strong advantages.

At the top of that list is this lens's bottom of the line price, half that of the next least expensive RF option at review time. The focal length has great general-purpose utility, and the wide aperture provides strong advantages over narrow aperture zoom lenses. The compact size and light weight mean there is always space and energy for the RF 50mm F1.8 to be in the kit. Having the lens along and the energy to use it means getting more and better images. That also means keeping the fun in photography.

The Canon RF 50mm F1.8 STM Lens is a great option for beginners, kids, those wanting a low light lens to complement a lower-end kit lens, those on a tight budget, or those needing the unique features this lens offers.