In summary
With its fast – and constant – f/2.8 maximum aperture, compact size and relatively light weight, coupled with weather-resistant sealing, the RF 28-70mm f/2.8 IS STM lens slot nicely between Canon’s entry-level and high-end offerings, giving potential buyers a wider choice of standard, short-zoom lenses.
Full review
Announced in September 2024, the RF 28-70mm f/2.8 IS STM lens is the 50th lens to be released in the still-growing RF range. Weighing only 490 grams and just 92.2 mm long when retracted, it’s one of the lightest in its class and can be used on cameras with full-frame sensors as well as cropped-sensor models like the EOS R7, EOS R10, EOS R50, EOS R100 and EOS R50V, where its effective zoom range is equivalent to 44.8-112mm. Unfortunately, Canon appears to view it as a ‘budget’ lens, despite its relatively high price tag. This is why it’s sold without the bundled EW-73D lens hood, which costs an additional AU$50.
Angled view of the RF 28-70mm f/2.8 IS STM lens without end caps. (Source: Canon.)
The RF 28-70mm is much smaller and lighter than its L-series sibling, the RF 28-70mm f/2.8 L USM, and less than half its price. Its optical design contains 15 elements in 12 groups and includes two Ultra-low Dispersion (UD) elements, the larger of which is located towards the front of the barrel as shown in the optical diagram below.
These two diagrams show the positions of the lens elements when the lens is retracted and extended. (Source: Canon.)
The second, smaller UD element sits behind the IS group and helps to correct chromatic aberration and reduce the weight of the front lens group. In addition, two glass-moulded aspherical elements, one of which comprises the IS group, have been used for suppressing other aberrations.
Super Spectra Coating (SSC) has been applied to suppress backlit flare and ghosting, while maintaining light transmission and image contrast. A rounded nine-blade diaphragm produces a pleasing bokeh quality.
Autofocusing is driven by a lead screw stepping motor, which operates smoothly and silently and provides precise focus control. Focus is controlled from the camera, which means manual focus over-ride is supported.
This diagram shows the positions of the sealing rings that keep out moisture and dust. (Source: Canon.)
The RF 28-70mm f/2.8 IS STM lens has similar weather-resistant sealing to Canon’s L-series lenses – and also uses L-series glass in its optics (which could account for its relatively high price tag). The relatively fast f/2.8 constant maximum aperture gives this lens some advantages over slower and cheaper alternatives, particularly for photographers who require more pleasing bokeh and increased light-gathering capabilities for portraiture and low-light shooting.
Who’s it For?
The 28-70mm zoom range and fast f/2.8 aperture make this lens well suited to a wide range of genres, from landscapes and street photography to portraits and product shots. It can also be used for videography thanks to good control of focus breathing, which supports smooth rack focusing.
Alt less than half the price of the RF 28-70mm f/2.8 L USM, it’s also about a third of its weight and significantly smaller. It is also stabilised, using up-to-date IS technology, which is rated at five stops for the lens alone and seven stops when combined with the camera’s IBIS.
Build and Ergonomics
Canon doesn’t specify what the lens barrel is made from, although it’s probably high-quality engineering polycarbonate on a metal inner barrel and mount. Unlike its L-series sibling, the RF 28-70mm f/2.8 IS STM lens has only two rotating rings, a programmable control ring, which is present in all RF lenses, and a zoom ring.
The front element has a diameter of approximately 55 mm and is surrounded by a partially-ribbed annulus that is 10 mm wide and extends outwards to meet the 67 mm diameter, raised filter thread. There is a bayonet moulding on the outside rim for the optional lens hood.
The control ring, which is not clicked, can be programmed for quick access to settings like lens aperture, ISO and exposure compensation, and also doubles as the focus ring in manual focus mode. It is located behind a thin grey ring approximately 10 mm back from the front of the outer barrel and completely clad in fine hatching to provide a secure and comfortable grip.
Five millimetres behind the control ring is the zoom ring, which is 26 mm wide and is partially covered by a narrowly-ridged rubber grip band. The un-ridged trailing edge carries stamped marks for the 28mm, 35mm, 50mm and 70mm focal length settings.
Behind the zoom ring is a 25 mm wide band that carries the AF/MF and Stabiliser on/off switches. This band ends in an indented edge that covers the end of the inner barrel, which carries the lens mount index mark.
The inner barrel ends in a rubber ring which prevents moisture and dust from entering via the solid metal lens mount. There is no distance scale or depth of field indicator but Canon’s EOS R cameras can display this information in their EVFs.
Performance
Our Imatest tests showed the review lens came close to meeting expectations for the 44-megapixel sensor on the EOS R5 II camera we used for our tests for both JPEG and CR3.RAW files at optimal aperture settings. The highest resolution was recorded at the 35mm focal length with an aperture of f/4.
Although some edge softening was measured (and expected) at wider apertures, it was greatest at 28mm and relatively minor at the 70mm focal length. Fortunately, the overall performance across the aperture range was very good, with diffraction only taking effects at around f/16, as shown in the graph of our test results below.
In line with our normal practice, we disabled all in-camera processing of JPEGs before assessing vignetting and rectilinear distortion. But we still made all measurements on raw files, which had been converted into TIFF format using Adobe Camera Raw.
Some vignetting was apparent at f/2.8 with all focal length settings, although it had been largely eliminated by f/4. Stopping down beyond this point removed edge darkening.
We found obvious barrel distortion in uncorrected files at 28mm and obvious pincushion distortion at 70mm but only slight pincushioning at 50mm and very little distortion at 35mm. Fortunately, it is fully addressed by activating in-camera corrections and neither aberration would be problematic for normal shooting.
We found evidence of both purple and green fringing in uncorrected shots taken at 28mm. None was at longer focal lengths, although edge softening made it more difficult to pick potential fringing up. This fringing can be corrected automatically in the camera as well as with most raw file converters so it’s not really a problem.
Autofocusing was fast and accurate when shooting normal subjects in bright conditions, as well as virtually noise-free, which will please videographers. Subject recognition worked well for picking up human faces, even in relatively dim lighting.
The minimum focusing distance of 27 cm provided some scope for shooting close-ups, particularly at longer focal lengths. The relatively wide maximum aperture provides good opportunities for control over depth of focus, especially at longer focal lengths.
Bokeh at wide aperture settings was smooth at longer focal lengths, especially in low-contrast areas. While some soft outlining could be seen around brighter areas at 70mm, at 28mm the outlining became more obvious and traces of the ‘onion skin’ effect began to appear.
Stopping the lens down to f/22 produced 18-pointed sunstars around direct light sources within the frame although they were somewhat diffuse and disappointing at longer focal lengths. However, they weren’t associated with flare artefacts.
Conclusion
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SPECS
Picture angle: 75 degrees 23 minutes to 34 degrees
Minimum aperture: f/22
Lens construction: 15 elements in 12 groups (including 2 UD and 2 aspheric elements) coatings
Lens mounts: Canon RF
Diaphragm Blades: 9 (circular aperture)
Weather resistance:
Focus drive: Lead screw stepping motor
Stabilisation: Yes, CIPA rated at 5.5 EV
Minimum focus: 27 cm
Maximum magnification: 0.24x
Filter size: 67 mm
Dimensions (Diameter x L): 76.5 x 99.3 mm
Weight: 495 grams
Standard Accessories: Front and rear caps
Distributor: Canon Australia
TESTS
Based on JPEG files taken with the Canon EOS R5 II camera.
Based on CR3.RAW files converted into 16-bit TIFF format with Adobe Camera Raw.
SAMPLES
Vignetting at 28mm f/2.8.
Vignetting at 35mm f/2.8.
Vignetting at 50mm f/2.8.
Vignetting at 70mm f/2.8.
Rectilinear distortion at 28mm.
Rectilinear distortion at 35mm.
Rectilinear distortion at 50mm.
Rectilinear distortion at 70mm.
Close-up at 28mm, f/2.8; 1/4000 second, ISO 200.
Close-up at 70mm, f/2.8; 1/5000 second, ISO 200.
28mm focal length; 1/200 second at f/9, ISO 100.
Crop from the above image magnified to 100% showing coloured fringing.
70mm focal length; 1/200 second at f/9, ISO 100.
Sunstar at 28mm, f/22; ISO 100, 1/80 second.
Sunstar at 70mm, f/22; ISO 100, 1/60 second.
28mm focal length, 1/160 second at f/7.1, ISO 200.
70mm focal length; 1/500 second at f/11, ISO 200.
63mm focal length; 1/1200 second at f/6.3, ISO 100.
70mm focal length; 1800 second at f/6.3, ISO 200.
70mm focal length; 1/500 second at f/8, ISO 200.
28mm focal length; 1/160 second at f/5, ISO 400.
64mm focal length; 1/60 second at f/2.8, ISO 200.
70mm focal length; 1/100 second at f/5.6, ISO 400.
70mm focal length; 1/200 second at f/4.5, ISO 200.
28mm focal length; 1/100 second at f/5, ISO 400.
28mm focal length; 1/20 second at f/9, ISO 200.
55mm focal length; 1/100 second at f/4.5, ISO 200.
Rating
- Build: 8.8
- Handling: 8.9
- Image quality: 9.0
- Autofocusing: 9.0
- Versatility: 8.9
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