Review by Klaus Schroiff, published February 2022
Introduction
When the first pictures of the Canon RF 16mm f/2.8 STM lens emerged, the Canon community was bursting with excitement – and a lot of questions. The world hadn’t seen a tiny 16mm f/2.8 full format lens to date so some, including yours truly, expected it to be an APS-C format lens similar to the Sony E 16mm f/2.8. But it turned out that it is indeed a full format lens at a price tag that hasn’t been seen in this lens class either. Priced at just $300/350EUR, Canon surprised all of us, I reckon.
However, what can we expect from such a bargain offer? Let’s see.
In terms of construction, it is almost identical to the Canon RF 50mm f/1.8 STM. If it weren’t for the focal length printed on the barrel and the inner lens tube, you wouldn’t be able to tell them apart (see the comparison below). Even the filter size (43mm) is the same, baffling considering the immense front element that we have seen on other ultra-wide lenses in this speed class. However, the similarity also means that the build quality is more aligned with consumers than professionals. The lens body is made of plastics based on a metal mount. It’s a retractable design so once you activate the camera, the inner lens tube moves a little out into its working position. There is a single control ring that is either assigned to manual focusing or a custom function – and there’s a switch for selecting the desired mode. Weather-sealing is absent and you won’t find a lens hood in the package.
The lens uses an STM (stepping motor) for focusing – both in AF and MF mode. While full-time-manual focusing in AF mode is supported, fully manual focusing has to be activated
via a camera menu setting. Thanks to the minimal weight of the inner tube, the AF speed is pretty fast. It emits a high-pitched sound during operation, but it’s on a low noise level. Another surprising aspect of the lens is its close-focus capability with a maximum magnification of 1:3.8. This isn’t macro territory yet but it’s closer than possible on most ultra-wide lenses in this respect. An image stabilizer has not been implemented.
| Specifications | |
|---|---|
| Optical construction | 9 elements in 7 groups including 1x aspherical element |
| Number of aperture blades | 7 (rounded) |
| min. focus distance | 0.13m (max. magnification ratio 1:3.8) |
| Dimensions | 69.2×40.5mm |
| Weight | 165g |
| Filter size | 43mm |
| Hood | petal-shaped (bayonet mount, optional) |
| Other features | Combined Focus/Control ring |
Distortion
The lens produces a native barrel distortion of almost 10%! This is excessive, making it basically unsuitable for use without digital correction. The latter does an excellent job by reducing the issue to essentially zero. While this is commendable, there is a price to pay for this because the image is stretched substantially, thus reducing resolution in the outer image field.
Vignetting
Let’s do a three-stage analysis of the vignetting characteristic this time. Without any distortion and vignetting correction, the light falloff is extreme. At f/2.8, the corners are essentially black and not much brighter at f/4. The vignetting exceeds our usual scale even at f/11.The problematic corners are getting pushed off the frame with activated distortion correction but deactivated vignetting correction. The vignetting is still heavy at f/2.8 but not terrible when stopped down, considering the ultra-wide nature of the lens. With full correction enabled, the results are quite good even at f/2.8 because the light falloff is very gradual from the center to the corners. Needless to say but the signal boost comes at the cost of increased image noise in the outer image field.
The 2 images below show the fully corrected and fully uncorrected vignetting.
MTF (resolution) at 45 megapixels (EOS R5)
Usually, we test the resolution in uncorrected mode because the quality of the correction is also heavily dependent on how it is performed, and unless the distortions exceed 4%, there isn’t much of an impact anyway. However, it makes no sense to do so in this specific case. The Canon RF 16mm f/2.8 STM is just not designed for being used without correction. The resolution characteristic is fairly predictable from here. The broader center quality has no issues whatsoever. The lens is tack sharp here, especially when stopped down a little bit. The borders and corners are an entirely different story, though. The borders are Okayish at f/2.8, but the corners are a pixel soup at this setting. Stopping down lifts the borders to reasonable levels, but the corner softness improves only marginally. This is all a bit tragic because, unsurprisingly, the lens appears to be much sharper without distortion correction.
The centering quality of the tested sample was good. The field curvature is low.
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure of sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations
MTF (resolution) at 30 megapixels (EOS R)
Not everybody has an EOS R5, so some of our readers are surely interested in how the lens performs on a more sanely priced camera – and it’s good to have a comparison with the existing set of 30mp-based reviews anyway.
As you can see below, the general theme remains similar – although the reduced megapixels are boosting the outer image quality (on pixel level) quite a bit. While there’s still some softness at f/2.8, the results are actually decent at medium aperture settings.
Please note that we apply a MILD amount of sharpening during the RAW conversion, and sharpening is more receptive to cleaner edges on lower megapixel images, so, besides other reasons, the MTF numbers obtained with the EOS R are NOT comparable to the R5 variant.
Chromatic Aberrations (CAs)
Uncorrected lateral CAs are very visible at around 2.5px at the image borders. This can be auto-corrected without loss of quality.
Bokeh
The Canon RF 16mm f/2.8 STM is a simple being with just a single aspherical element helping in its quest for quality. However, simple lens designs tend to produce a good bokeh. While certainly not meant for shallow depth-of-field photography, the bokeh is pleasing in the broader image center (shown to the right) – at very close focus distances, of course. The bokeh does deteriorate at the borders/corners as you can see to the left below.
Sample Images
The Canon RF 16mm f/2.8 STM is a lens with many facets. It comes down to where you come from and what you want. For instance, if you own an EOS R3 or R6, it's a decent ultra-wide prime lens - because, at 20 megapixels, even a Coke bottle is sharp enough. Well, almost. While on an EOS R5 and 45 megapixels, you don't really want to look at the image corners. It is, of course, also worth noting that this is the cheapest, fast ultra-wide prime ever released from a genuine manufacturer. Even when ignoring all quality concerns, it's dirt cheap for what it is. If you can't afford the real thing, having a 16mm ultra-wide lens is better than having none at all.
From a technical standpoint, the RF 16mm f/2.8 STM offers poor quality on a high megapixel camera. The broader center is perfectly sharp but the quality is falling apart in the corners. And that's with auto-correction. The lens is basically unusable in pure RAW mode with excessive barrel distortion, extreme vignetting and high lateral CAs. It's about as underdesigned as it gets and relies heavily on digital correction to lift it back from the imaging abyss. With auto-correction applied, there's only a mild amount of barrel distortions, the vignetting is low even at f/2.8 and the CAs have been killed off.The build quality is good for a consumer-grade lens, especially in this price class. It feels quite solid with a combination of plastic and metal parts and a smooth control/focus ring. It's also tiny and, as such, ideal for casual or street photography. On the downside, there is no weather sealing and it relies on a dated linear extension mechanism rather than internal focusing. This means that the STM has to move the entire lens system for focusing. However, there isn't much to move around anyway so the AF speed is entirely satisfactory.
Overall, you may argue that you get what you pay for but this isn't really true. A 16mmm f/2.8 for this kind of money is an insane bargain even with the mentioned limitations. Just don't expect Mercedes quality for a Lada price tag.
-
Optical Quality (45mp)
-
Optical Quality (30mp)
-
Build Quality
-
Price/Performance