This page contains reviews of RF28mm F2.8 STM.
Lens Summary
| Price | reasonably cheap |
| Size | Very small |
| Weight | Very lightweight |
| Ease of use | Simple but functional |
| AF performance | Some compromise is necessary |
| Resolution performance | Very good except for the corners |
| Bokeh | Good for this class |
| chromatic aberration | Very good |
| distortion | Correction Required |
| coma aberration | Good correction status |
| Vignetting | In some cases, correction is necessary. |
| flare resistance | Not very good |
| Overall evaluation | High-performance pancake lens |
Evaluation：
This is a small, lightweight, low-priced pancake lens that is of a high standard overall. Although it does have a few minor flaws, they are within the range that can be tolerated when you consider its high optical performance and incredible portability.
Foreword
- Release Date:2023.5.24
- Product page
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- B&H photo
- Adorama
This lens was released in July 2023. It is the smallest and lightest wide-angle lens in RF history, but it is compatible with full-size cameras. Its compact and lightweight lens size and convenient focal length are compatible not only with full-size cameras but also with APS-C cameras, and its affordable price and size make it a highly versatile single-focus lens.
Although it does not have image stabilization, it is less than half the length and weight of the EF28mm F2.8 IS USM SLR lens. The minimum shooting distance is the same, but the shooting magnification is lower, so it may not be suitable for close-ups. The focus drive is a stepping motor, so it may be lower than the EF lens with a ring USM.
The lens is made up of 8 elements in 6 groups, with PMo aspherical lenses used for the last 3 elements. The cross-sectional view is very characteristic of PMo lenses. Some people say that the cross-sectional view is similar to that of a smartphone camera, but I'd like to actually test it to see what kind of results it gives in real-life photography. By the way, although you can't check it on the official website, the aspherical lens used in the “RF16mm F2.8 STM”, “RF50mm F1.8 STM” and “RF24-50mm F4.5-6.3 IS STM” is also PMo.
specifications
| lens mount | RF |
| Supported sensor size | Full frame |
| focal length | 28mm |
| Lens construction | 8 lenses in 6 groups |
| Aperture | F2.8 - F22 |
| Aperture blades | 0.23m |
| Minimum focusing distance | 0.17 |
| Maximum magnification | ×0.17 |
| Filter diameter | 55mm |
| image stabilisation | - |
| Teleconversion lens | - |
| Coating | Super Spectra Coating |
| Size | φ69.2mm×24.7mm |
| Weight | 120g |
| weather sealing | - |
| AF | Stepping motor |
| Aperture ring | - |
| Other controls | AF/Control/MF Switch |
| Accessories | Lens Cap E-55 Lens Dust Cap RF |
RF28mm F2.8 STM Review
Appearance and operability
Boxes and accessories
The design is based around a black color that is characteristic of Canon RF. The packaging for the lens body differs depending on the product, and this lens does not use plastic dividers, but only uses an air cushion as a bottom sheet.
In addition to the lens itself, it comes with front and rear caps, an instruction manual, and a warranty card. The lens hood is sold separately, so if you need one, be sure to buy it separately.
Appearance
It is made mainly of plastic parts, but the mount is made of metal. The texture is not inferior to other RF lenses, and it is solidly made despite its small size.
The Canon logo is embedded on the surface, and the focal length, focus range, serial number, etc. are printed. It seems that the CE mark and other displays that cannot be erased are imprinted on the exterior parts.
Hands-on
It is palm-sized, which is the smallest and lightest RF lens. The diameter is larger to match the RF mount, but it is surprisingly thin for a full-size 28mm wide-angle lens. The inner barrel extends when in use, but it is very easy to store.
This lens is shorter in length and lighter than the compact RF16mm and RF50mm lenses in the RF lineup. The lens hood is also a compact screw-on design, making it far more portable and easy to store.
Front and back
Despite its compact size, the filter diameter is a relatively large 55mm. Considering that the RF16mm F2.8 and RF50mm F1.8 have a diameter of 43mm, this feels like an unnecessarily large filter size. Also, there are very few products with a 55mm diameter RF mount, and this lens is the only one for full-size cameras. It's a little disappointing that the filter is a specification that is difficult to use with lenses of the same diameter.
In contrast to the small front lens, the rear lens is larger. Furthermore, the last lens is positioned in a way that protrudes from the mount, so there is a higher risk of it being touched by a finger or damaged by being bumped into something. You should handle it carefully when attaching and detaching the lens. In addition, the country of manufacture, “Taiwan”, is printed around the rear lens.
Focus ring
It is equipped with a small plastic focus ring. Although it is a very small ring, the knurled surface provides a secure grip, and the rotation is smooth, enabling operation with moderate torque. For the size and price, it has good operability. The stroke during MF can be switched between “linear (rotation amount)” and “non-linear (rotation speed)” on the camera side. When set to rotation amount, it can be operated from the minimum shooting distance to infinity in about 135 degrees.
Switch
Like the “RF24-50mm F4.5-6.3 IS STM”, it is equipped with a newly designed 3-position switch. In addition to being able to switch between AF and MF, it can also be used as a control ring by adjusting it to the middle position. Until now, low-priced lenses did not have an “MF” position, and it was necessary to switch it using the camera's menu system. I think it is a very excellent design switch.
Example of use
Fits EOS R5, R8 and R7. It is a small and lightweight lens, and there is no sense of incongruity when attached to the compact EOS R8 or APS-C EOS R7. In fact, the body of the R5 seems too large for the lens. The EOS R8 and EOS R10 would be a good balance.
The maximum diameter of the lens is the same as the outer diameter of the RF mount. This means that even small cameras will not protrude below the outer diameter of the mount. There is no need to worry about interference when mounting on a tripod, etc.
AF・MF
Focus Speed
The focus group is driven by a geared stepping motor. Compared to a lead screw system, it is less responsive and quieter. However, when combined with the EOS R5 or R8, it works at a fairly good focusing speed, so I didn't feel any particular dissatisfaction in actual photography.
Breathing
Focus breathing refers to the change in the angle of view depending on the focus position.If the change in angle of view is significant, the field of view will expand or contract during focusing, potentially causing distractions and affecting autofocus stability. Ideally, it is better to have no focusing breathing. In order to check the effects of breathing, we took the following photos with the lens stopped down to the minimum aperture, at the minimum shooting distance and at infinity.
The angle of view changes greatly between the minimum shooting distance and infinity. When shooting video or focusing on the periphery, you need to be careful because the web ring operation is quite noticeable.
AF accuracy
As long as it is used in combination with the R5 or R8, there are no particular problems, and it is possible to focus at a fairly good speed even in low light. However, the image plane curvature is large even at infinity, so if you don't focus at the position you are aiming for, there is a possibility that you will miss the peak of the focus. In addition, due to the effect of focus breathing, the reproducibility of the focus position may decrease when trying to focus on the edge or corner of the frame.
MF
As mentioned above, it is possible to operate it with a linear response and moderate stroke. It is easy to operate with a smooth, moderate torque focus ring, and the gear-type stepping motor also operates smoothly.
Resolution Chart
Test conditions
- Camera body:EOS R5
- Interchangeable lens:RF28mm F2.8 STM
- Pearl Optical Industry Co.
‘[HR23348] ISO12233-compliant 8K resolution test chart (for still cameras)’ - Olympus HYRes 3.1 analysis software
- The lighting environment is constant indoors.
- Tripod, self-timer 10 seconds, electronic shutter
- RAW output
- ISO 100
- RAW development in Adobe Lightroom Classic CC
・Sharpness: Off
・Noise reduction: Off
・Chromatic aberration correction: Off - Focus on each point to be analysed and take a picture
(image plane curvature is difficult to measure at close range, so check at infinity) - Note that this is a test at close range (infinity may be even better).
- If you adjust the sharpness when developing JPEG or RAW images, the values may improve. Please note that the values given here are the ‘minimum values’.
Test results
You can get good results overall from open aperture. Although the edges and corners of the frame look inferior compared to the center, you can get results with high homogeneity by stopping down two stops.
Centre of frame
You can get very sharp results from wide open aperture. Even when stopped down, there is no significant improvement, and the performance is almost at its peak from F2.8. There is also no loss of contrast due to axial chromatic aberration or spherical aberration. It seems that this compact wide-angle lens achieves good aberration correction.
Middle of frame
Compared to the center, the details are a little soft, but there is no significant distortion in the image quality. The effect of chromatic aberration is also small, and if you stop down two stops, you can get a sharp result even in the details.
Four corners of frame
From f/2.8, the image quality is good with no significant roughness in the details. Although the chromatic aberration is a little noticeable, it is not excessive residual aberration. For a small, lightweight pancake lens, the results are surprisingly good. As with the periphery, the sharpness of the details improves when the aperture is set to two stops.
Sample
far-field resolution
Test environment
Date of shooting: July 11, 2023, cloudy, light breeze
Camera: EOS R5
Tripod: Leofoto LS-365C
Head: SUNWAYFOTO GH-PRO II
Exposure: Aperture-priority AE, electronic first curtain shutter, ISO 100
RAW:
Adobe Lightroom Classic CC development
Sharpness off
Lens correction off
Noise correction off
Test results
Although there is a slight drop in image quality in the corners of the frame, which may be due to field curvature, sharp results can be obtained over a wide range from F2.8. If you stop down to F4, the contrast will improve slightly and reach its peak. If you stop down to F5.6, you can get satisfactory results even in the corners of the frame. Although there is a slight effect of diffraction, you can get similar results up to F11, and the effect of diffraction becomes stronger at F16 and beyond. Overall, this is a good-performing, compact, lightweight, low-priced wide-angle lens.
Centre of frame
The contrast improves a little when you stop down to f/4, although it is already at its peak at f/2.8. There is no significant change after that.
Middle of frame
Basically, you can get the same results as in the center. The changes due to the aperture also follow the same trend.
Four corners of frame
Compared to the center and the periphery, F2.8~F4 is slightly soft. This is due to the influence of coma aberration, but also includes the influence of field curvature (see below). When the aperture is stopped down to F5.6, the various aberrations converge and the result improves to a sharp image. The peak is reached at F8.
curvature of a surface
What is surface curvature?
This refers to the fact that the shooting distance at which the image is in focus differs from the centre to the four corners. For example, even if the image is in focus at a shooting distance of 1m, if the subject is moving back and forth around 1m at the edge of the frame, there is a possibility of field curvature.
Although there are few lenses that have noticeable field curvature, in recent lenses, aberration may increase and become noticeable at close distances. However, there are few opportunities to take photos of flat subjects at close range, so even if there is some image curvature, there is no need to worry.
However, if there is an effect even at infinity, you should be careful. If you are trying to achieve a pan-focus effect, for example in a landscape, there is a possibility that you will end up with an unintentional out-of-focus image. As there is no way to correct this aberration, the only way to avoid the problem is to increase the F-number to widen the depth of field.
Test results
If you focus on the corner of the frame, you can get a sharp result from F2.8 only in the corner. However, the center area of the wide range will be out of focus and the result will be soft. If you want to get a pan focus, it is recommended to use the center area when focusing and to firmly narrow down the aperture to F5.6-8.
Lateral chromatic aberration
What is lateral chromatic aberration?
A colour shift that appears mainly around the edges and corners of the frame. Unlike longitudinal chromatic aberration, the effect of correcting this aberration using the aperture is small, so it is necessary to correct it at the stage of optical design. However, it is possible to digitally correct chromatic aberration using the image processing engine built into the camera body. This makes it possible to correct chromatic aberration, which is difficult to correct optically alone, and recently, there have been lenses that prioritise the correction of other aberrations over chromatic aberration correction. In particular, mirrorless systems tend to rely on post-processing.
Test results
Even when correction is turned off, aberrations are well suppressed across the entire aperture range. Any remaining aberrations can be easily corrected.
Longitudinal Chromatic Aberration
What is longitudinal chromatic aberration?
Longitudinal chromatic aberration is a colour shift that occurs in front of and behind the plane of focus. If the area in front of the plane of focus is mainly purple fringing, and the area behind the plane of focus has unnatural green colouring in the out-of-focus area, then the main cause is likely to be longitudinal chromatic aberration. This is more likely to occur with large-aperture lenses such as F1.4 and F1.8, and in such cases it is necessary to close down the aperture to improve the situation. It is possible to correct this using development software, but it is more difficult to process than lateral chromatic aberration, so it is best to suppress the aberration optically if possible. However, when suppressing longitudinal chromatic aberration with a large-aperture lens, the product price tends to be higher. Lenses that perfectly correct for longitudinal chromatic aberration have high contrast on the focal plane from wide open aperture, so you can expect a punchy resolution.
Test results
It's not perfect, but it's a good correction for a simple lens configuration pancake lens. There are almost no scenes where axial chromatic aberration is a problem from F2.8.
Distortion
What is Image Distortion?
Distortion refers to the phenomenon where straight lines do not appear straight on a flat surface. It is particularly noticeable when there are many straight lines, such as when there are man-made objects or a horizon in the image, and it can be divided into two types: barrel distortion, which is similar to that of a fisheye lens, and pincushion distortion, where the centre of the image appears compressed.
This is an aberration that can be corrected relatively easily, but it is difficult to manually correct distortions with complex shapes. In this case, a correction profile that matches the lens is required.
Test results
The uncorrected RAW image shows a barrel-shaped distortion that is slightly noticeable. The deformation is not linear, but rather has a slightly conical distortion, so it is difficult to correct manually. Fortunately, it is possible to correct it using a profile in major development software. Also, for a compact, lightweight, and reasonably priced wide-angle lens for mirrorless cameras, the aberration is well suppressed (it is not extreme distortion).
Coma aberration
What are coma and astigmatism?
Coma and astigmatism are mainly the failure of a point of light to appear as a point of light in the four corners of the frame. For example, this can be seen in artificial lights, stars and illuminations in night scenes. Even during the day, bright point light sources such as sunlight filtering through trees can also have an effect. As this problem cannot be corrected in post-processing, it is necessary to correct it optically.
Although it can be improved by narrowing the aperture, in situations where shutter speed is important, such as night scenes and astrophotography, it is not possible to narrow the aperture, and optical correction may be necessary.
Test results
The image extends in a radial direction, but there is no noticeable concentric deformation like a sagittal coma flare. Although not perfect, the correction is satisfactory.
Spherical aberration
There is no significant change in the bokeh quality before and after, and it appears that spherical aberration is being well corrected.
Foreground and background blur
What is a beautiful blur and a busy blur?
The evaluation of bokeh tends to be subjective, but I personally think that ‘soft, diffused bokeh’ is beautiful, while ‘sudden bokeh or hard-edged bokeh’ is not so good (or is a unique depiction). However, everyone has their own preferences, so there may be people who prefer the opposite. For reference, here are some examples of ‘blurred bokeh’ and ‘hard-edged bokeh’. The difference in the tendency of the depiction is mainly due to the state of correction of spherical aberration, and when the bokeh on either side is soft, there is a tendency for the bokeh on the other side to become hard.
Back Blur
The background bokeh is smooth and beautiful. In comparison, the foreground bokeh has a hard outline and shows signs of double bokeh. As there are few opportunities to include foreground bokeh with a 28mm lens, the texture of the background bokeh can be positively evaluated. The correction of axial chromatic aberration is not perfect, and some coloration occurs, but this is not a particularly big problem.
Front Blur
Bokehball
Effects of Vignetting and Spherical Aberration
If vignetting is strong, the bokeh at the four corners of the frame will be elliptically deformed or partially missing. The only way to solve this problem is to close down the aperture. However, closing down the aperture will make the bokeh smaller and in some cases the shape of the aperture blades may become visible, so it is necessary to compromise on the amount of vignetting depending on the situation.
If the amount of vignetting is small, it is possible to get a circular bokeh from wide open to the four corners. Ideally, a lens with little vignetting is preferable, but to eliminate it, it is necessary to fundamentally increase the size of the lens. There is a need to strike a balance between portability and cost, so some kind of compromise is necessary.
If the correction of spherical aberration is not perfect, there will be a difference in the depiction of the bokeh in front and behind (as shown in the review of bokeh in front and behind). In this case, one side will have a smooth depiction with blurring, while the other side will have a hard depiction like double-line bokeh.
Test results
Although there is some vignetting, the surface is smooth and clean. There is some vignetting towards the edges and corners of the frame. Vignetting can be improved by stopping down one stop, but the aperture shape becomes a little more angular. Compared to large-aperture portrait lenses, the results are not as good, but for a compact, lightweight F2.8 pancake lens, the results are better than expected.
Sample of a boke
Close range
The background is smooth and soft throughout. Although there is some vignetting, the bokeh is large and does not stand out too much. If you stop down one stop, the vignetting will be reduced, but the overall rendering will become a little harder and the outlines will become more noticeable.
Short range
As the shooting distance increases, the bokeh naturally becomes smaller. Nevertheless, the overall smooth and beautiful depiction is maintained. The bokeh quality is easy to incorporate into photos, with no noticeable outlines or chromatic aberration towards the corners of the frame. The depiction is far better than that of the Nikon “Z 26mm F2.8”, which is also a pancake lens.
Medium range
If the shooting distance is even longer, it will not be possible to achieve a large bokeh effect with the “28mm F2.8” lens to begin with. The contours of the background will remain clearly visible, so it will be difficult to isolate the subject using depth of field alone. The bokeh in this case is not bad, but the periphery and corners may become a little noisy due to the influence of coma aberration.
Portrait
The following are the results of taking pictures of a tripod that is 170cm tall while changing the distance and aperture.
It is difficult to blur the background when the whole body is in the frame. You should at least get close enough to blur the area above the knees and waist. A satisfying amount of blur can be obtained from a close-up of the bust to a close-up of the face, and the texture at this time is also sufficiently good.
Vignetting
What is vignetting?
Unnatural drop in light intensity around the frame.
The light intensity is lower than in the central area, and there is insufficient exposure in the four corners of the frame. This mainly occurs with large-aperture lenses and wide-angle lenses.
Although this is a phenomenon that can be easily corrected using software, it is necessary to be careful about the fact that it can cause noise, as the insufficient exposure is covered by post-processing correction (sensitization). In particular, when using high sensitivity for nightscape or starry sky photography, there is a possibility that noise will appear strongly.
Minimum focusing distance
Vignetting is noticeable at F2.8. It can be improved by stopping down the aperture, but it will not disappear throughout the entire aperture range. Lens correction is essential if you want to obtain a flat exposure.
Infinity
The vignetting is stronger than the minimum shooting distance. The amount that remains when the aperture is narrowed is also a little high. This may be a positive thing, but basically you should think that correction is essential.
Backlight resistance, sunstar
centre
This is a weak point of this lens. Although it has a small number of lens elements, it produces noticeable flare and ghosting in backlit conditions. Although this is not a bad result in terms of image quality, it is not a good result in terms of backlit resistance. When you stop down the aperture, various factors combine to produce a noisy image, including RGB ghosting that appears to be caused by reflections on the sensor surface, ghosting between the fine lens elements, and dispersed light streaks.
corner
When the light source is moved to the corner of the frame, the ghosting and flare appear to be well suppressed. However, when the aperture is narrowed, some noticeable ghosting occurs on the diagonal line around the light source.
sunstar
The streaks of light appear from around F11, and then change to sharp depiction from F16 to F22.
Summary
Good points
Compact and lightweight
(relatively) affordable
3-way control switch
Compact but easy-to-use control ring
Stable resolution performance even at short distances
Good long-distance resolution from F2.8 except at the four corners
Good chromatic aberration correction
Smooth depiction with a soft background
Smooth bokeh
Good coma aberration correction
For a small, lightweight, reasonably priced pancake lens, the optical performance is unexpectedly good. Although there are some compromises in certain areas, the lens is sharp from F2.8 over a wide range. In particular, for a lens of this type, the bokeh is very smooth and beautiful. As it is a full-group extension type, the depiction when shooting close-ups is also stable, making it a versatile lens that is good for both close-ups and long-distance shots.
Bad points
Not dustproof or splashproof
Maximum aperture of F2.8
Lens hood sold separately
Focusing by all-group extension
Cannot protect inner barrel with lens hood
Focus breathing, AF drive noise
Vignetting
Barrel distortion is noticeable
Peripheral illumination is noticeable
Backlight resistance
There are various faults, but none of them are serious problems. If I had to say something, I think it would be that it would have been nice to have a hood to protect the inner barrel of the focus-pulling mechanism. Although there are noticeable optical distortions and vignetting, these can be corrected beautifully using camera-side correction. There is nothing that can be done about field curvature, but if you don't have excessive expectations of using F2.8 for pan-focusing, you won't be disappointed.
Conclusion
This pancake lens is compact and lightweight, yet high-performance and easy to use at an affordable price. Despite its few shortcomings, it is the perfect lens for when you want to casually take photos while walking around with a compact system, or for travel where portability is a priority. It has an easy-to-use angle of view even when attached to an APS-C, and it has optical performance that can withstand high resolution of 30 million pixels. At first glance, the “28mm F2.8” may not seem like an attractive parameter, but I think that if you use a variety of lenses and then try this one, you will notice how good it is.
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