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Sunday, 20 August 2023

Canon RF 28mm f2.8 STM lens user review 20 August 2023

 



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



This is an extreme crop from the full frame. Grevillea sericea at about the upper left intersection of thirds on the frame showing the  amount of detail which this body/lens combination can transfer from subject to picture.  R5 with RF 28mm f2.8

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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