In recent years Canon has shown it is willing to explore
unconventional approaches to lens design and construction in the quest for high
quality at a consumer friendly price.
The recently released RF 28mm f2.8 STM lens is a good
example of this.
Design and construction of the RF 28mm f2.8 STM is very
different from that of either the EF 28mm f2.8 (without IS) or the EF 28mm f2.8
IS USM. Both these DSLR lenses have a large front element and smaller rear elements. The new lens turns
this around with a tiny front element only 10mm in diameter, an aperture
diaphragm close to the front lens group and three very large, strongly
aspherical semi rectangular plastic moulded elements at the rear, backed by a
protective glass flat.
The published modulation transfer chart (MTF) for the lens
suggests very high sharpness across the frame right from f2.8. My tests show
that is in fact what the lens delivers. The new RF lens is much better
particularly at the edges of the frame at f2.8 than either of the older EF
lenses.
The RF 28mm f2.8 is the smallest lens in the RF catalogue
and at 24.7 mm without a filter or lens cap one of the shortest full frame
lenses we will find in any system.
The lens lacks a stabiliser so is best used on one of the RF
bodies with IBIS where it makes for a very compact yet optically excellent
carry-around kit suitable for many photographic challenges. At the time of
writing the Canon RF mount bodies with IBIS are R3, R5, R6, R6.2, R7.
The lens can also be used on one of the RF bodies with the
APSC crop sensor when it becomes equivalent to 28 x 1.6 = 45mm which is a handy
general purpose standard focal length.
The only RF-S crop sensor body with IBIS at the time of writing is the
R7.
Some details
The lens is made in Taiwan along with most of Canon’s
consumer level lenses.
The focal length is 28mm. Maximum aperture f2.8. Diameter 69mm,
length from camera mount face to front of lens when retracted, without filter
or cap 24.7mm, with filter and cap 38mm,
mass with B+W protect filter, front and rear caps 182 grams.
The mount is metal. My copy is quite tight on the mount
while still new.
There is a thin control ring at the front of the barrel. A
sliding switch behind this selects function of the ring, MF/Control/AF. There
is no stabiliser switch on the lens presumably because there is no stabiliser
in the lens. IBIS status has to be set in a menu.
Lens construction is 8 elements in 6 groups with three
plastic moulded aspheric rear elements and a glass protective flat at the rear
which Canon counts as one of the elements. The inner barrel protrudes 1mm when
powered on and up to 5mm further when focussed close. So it is a front
focussing design like other recently released RF mount consumer primes. The
whole lens construction (but not the rear optical flat) moves as a single unit
when focussing.
The rear element protrudes 9mm behind the mount which places
it only 6mm in front of the focal plane shutter which sits 15mm behind the
mount with the sensor 20mm behind the mount. In a DSLR there has to be a substantial
(in camera terms) space between the back of the lens and the sensor to enable
the reflex mirror to flip up and down. But in a modern mirrorless design there
is hardly any un-occupied space in this region at all.
The EW-55 screw-in hood is not supplied with the lens as is
Canon’s usual practice with non-L consumer lens models. For what it is worth I
routinely get annoyed by this practice on the basis that making the hood might
cost Canon maybe a dollar so why not win friends and customers by putting one
in the box with every lens.
There are no bayonet lugs for a petal type hood.
There is no image stabiliser in the lens. Weather sealing is
not advertised.
Filter size is 55mm.
Focussing is by stepping motor (STM)
Performance
Autofocus is smooth and decently fast enough for any purpose
for which this lens is likely to be used. Focus noise is audible if we are
close to the lens. Accuracy is very good with a high level of consistency. All
Canon’s latest AF capabilities work well on this lens. As usual with Canon the
lens establishes exposure and focus wide open then closes down to the set
aperture to take the picture.
The effective angle of view changes visibly when focussing
(focus breathing) which is typical of lenses which focus by moving the whole
optical formula. We can easily understand that as we focus closer by moving the
lens away from the sensor, this increases the effective focal length and
decreases the angle of view.
Half macro close-ups are not available. Maximum
magnification is only 0.17x.
Optical
My copy is well centered with no significant difference in
sharpness from corner to corner.
On my standard tests I find that sharpness, clarity,
contrast and resolution are in the excellent to outstanding range right from
f2.8 and right across the frame with just a hint of softening in the far
corners at f2.8.
The 28mm f2.8 delivers resolution equal to or in some parts
of the frame marginally better than my
RF 100mm f2.8 L macro which is an extremely sharp lens. This is quite unusual for a wide angle lens as
most of these do not deliver their best wide open.
Overall sharpness declines just a touch at f11 and
noticeably at f16 due to diffraction.
Because of this I use the lens at f11 for landscapes with a
close foreground and f8 when the foreground is not too close to the camera.
Uncorrected Raw files exhibit moderately strong barrel
distortion although this is almost fully corrected in JPGs or with the Adobe
profile. This is easy to correct fully for architectural work as is the mild
degree of corner shading at f2.8.
Color fringing is very well controlled with just a touch of
purple fringing becoming evident on high contrast edges near the corners of the
frame.
The out of focus characteristic (bokeh) does not attract any
adverse attention to itself being generally smooth without ni-sen.
Veiling flare can be induced quite easily with the sun in
the right (or wrong, depending on our expectations) position just outside the
frame. I find this occurs with or without the protect filter. In the field I
deal with this by holding my left hand where it will block the sun’s rays from
falling on the camera. We can easily see the veiling flare in the viewfinder
when it occurs.
I will update this section when the EW-55 lens hood becomes
available in Australia.
About the plastic
elements
In his review of this lens and teardown with a Canon
representative, Gordon Laing of CameraLabs points out that Canon has been using plastic
moulded lens elements since 1982. They have appeared in many EF-S and EF-M
lenses and nine consumer grade RF lenses to date, both primes and zooms. As it
happens I own a copy of each of these and I find them to be optically very good
to excellent.
It appears us photographers have been happily using plastic
moulded aspheric lens elements for years with no reported problems.
However never before the RF 28mm f2.8 have we seen such extensive use of PMO
aspherics in a lens and none with such dramatically shaped non spherical
elements.
The proof, as they say, is in the pudding. And the RF 28mm
f2.8 delivers a remarkable level of imaging capability. It is in this regard as
good as any wide angle lens I have seen from any lens maker at any price point.
This is the full frame. Hand held RF28mm f2.8 on R5 at f11 |
In the field
In the urban jungle the RF 28mm f2.8 on an RF mount body
with IBIS makes for a compact, capable kit which can easily manage any kind of photographic
challenge for which a medium wide angle view is appropriate, indoors or
outdoors.
In the bush the same combination is no less impressive. I
have been using the RF 28/f2.8 on my R5 to make what I call flowerscapes in the
bushland around Sydney, some parts of which are a riot of wildflowers in late
winter and early spring. The problems photographically are that the individual
flowers are generally very small, they co-exist with a tangle of trees,
branches, leaves, and physically complex heath species, the slightest breeze causes the whole lot to
wave about and conditions are often bright and sunny creating specular
highlights on leaves and deep shadows.
A tripod is no help
because the little flowers are moving about in the breeze. A larger format
camera would be no help because of limitations on depth of field. In the event the best equipment solution is
the one which I now have. That is a high pixel count full frame camera with a
24 x 36mm sensor and high dynamic range, fronted by a medium wide lens able to
deliver very high levels of subject detail to the sensor with enough depth of
field for the subject.
A bonus is that the body + lens kit is not significantly
more bulky than some compact cameras such as the Leica Q (Q2, Q3).
It’s a winner.
30 September 2023 Update with JJC LH EW-55 Lens hood
The RF 28mm f2.8 has a control ring right at the front of the lens barrel so there is no possibility for fitting a standard bayonet mount lens hood. Canon offers the EW-55 srew-in hood for this lens. I got the JJC version which is considerably less expensive and is available.
The bare lens protrudes 24.5mm from the mount. I have a B+W protect filter fitted which adds 4.5mm. The JJC hood adds a further 9.5mm and the standard Canon lens cap 8mm.
I want the filter in place for two reasons,
First it protects the front element from the salt spray, dust, pollen and other junk which is often part of my photographic environment.
Second, this lens has the smallest front element I have ever seen on an interchangeable lens camera, making the task of cleaning it more fussy than would be the case with larger glass.
But the hood mounted in front of the filter vignettes the corners of the image at f2.8 and f4.
The fix for this is to file out the aluminium hood in four locations corresponding to the corners of the image. This gives the correct position for the alterations with the specific filter in place. To ensure no vignetting with any filer up to around 4.5mm thick, file out the whole of the smooth surface part of the hood, as seen from the front.and black out the bright surfaces.
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