Currently Canon’s widest RF lens, the groundbreaking RF10-20mm f/4L IS STM is high on portability, being half the size of its renowned EF counterpart. At the same time, it boasts outstanding performance that rivals if not exceeds the latter, along with new features such as up to 5 stops’ built-in image stabilisation.  Photographer Minefuyu Yamashita took it to capture the seascapes of Okinawa, and here’s his review. (Reported by Minefuyu Yamashita, Digital Camera Magazine)

EOS R5/ RF10-20mm f/4L IS STM/ FL: 10mm/ Aperture-priority AE (f/8, 1/500 sec, EV -0.3)/ ISO 200/ WB: Daylight

Overview: Photographer’s impressions

Astoundingly compact: ultra-wide-angle shooting is a breeze!

When I first picked up the RF10-20mm f/4L IS STM, I was so surprised by how small it was that I swear my heart skipped a beat! The lens’ specifications had prepared me to expect something compact, but in real life, my expectations were exceeded. It is similar in size to the RF14-35mm f/4L IS USM, another professional grade ultra-wide-angle zoom known for its portability.

I had been using the EF11-24mm f/4L USM, a stellar performer whose one weakness was its size: a hefty 1,180g. Weighing less than half of that at only around 570g, the RF10-20mm f/4L IS STM is smaller and lighter despite a wider wide-angle end, built-in image stabilisation, and performance on par if not better. It’s a sign of just how much technology has advanced.

New eyes, new perspectives

The more I used the lens, the more I began to feel that the lens was teaching me new ways to see things. This was especially so at the 10mm end, where the effects of the extreme ultra-wide-angle perspective make you see objects and scenes in a new light. As a result, you compose things differently, and find yourself breaking away from your usual way of shooting.

Outstanding optical quality

Optical quality was impeccable throughout the entire zoom range, even at the maximum aperture where many other lenses tend to be softer. It’s a lens you won’t think twice about using at any time of the day, even under harsh afternoon light or at night—as you’ll see in the images that follow.

Here’s a closer look at 5 different aspects of the lens, along with sample images.

1. Image quality

#1: Image quality

Fine rendering of details from the centre to the edges

EOS R5/ RF10-20mm f/4L IS STM/ FL: 10mm/ Aperture-priority AE (f/8, 1/500 sec)/ ISO 200/ WB: Daylight

Close-up crops

Even at 10mm, details are breathtakingly sharp and well-resolved from the image centre all the way to the edges. Look at the close-up of the leaves at the bottom right edge of the image: I was surprised by just how clearly resolved they were, right down to the thorns!

The clarity remains throughout the image with no muddiness or colour blurring, testament to the efficient lens design.  This will be huge advantage not just for architectural shots, but also nature photography which is full of organic lines.

 

2. Image stabilisation

#2: Image stabilisation

The freedom to use a slower shutter during handheld shooting in low light

EOS R5/ RF10-20mm f/4L IS STM/ FL: 20mm/ Aperture-priority AE (f/4, 1/15 sec, EV -0.3)/ ISO 200/ WB: Cloudy

This is a handheld shot of twilight from a bridge. 10mm captured the bridge railings, but because this is a zoom lens, you have flexibility: turning the zoom ring to 20mm kept them out of the composition.

The lens’ optical image stabilisation (Optical IS) lets you use shutter speeds as much as 5 stops’ slower than the conventional “1/focal length” seconds you need to avoid blurring from camera shake. When used with a camera body with In-Body IS, the effect goes up to 6 stops’ equivalent. This allowed me to shoot handheld even in low light conditions like this while keeping the ISO low.

3. Backlight performance

#3: Backlight performance

2 coatings that reduce ghosting and flaring

EOS R5/ RF10-20mm f/4L IS STM/ FL: 10mm/ Aperture-priority AE (f/14, 1/800 sec)/ ISO 400/ WB: Daylight

As a seascape photographer, I see many wide-angle lenses having trouble with the emerald-green ocean in backlight. However, the RF10-20mm f/4L IS STM rendered the colours clearly and beautifully. That’s amazing considering how the wider the lens, the more prone it is to issues caused by reflections in the lens: light enters the lens from a greater variety of angles.

While the EF11-24mm f/4L USM used vapour deposit coatings to reduce ghosting, the RF10-20mm f/4L IS STM uses SWC (Subwavelength Structure Coating) and ASC (Air Sphere Coating), which are better at preventing internal reflections. The excellent backlight performance I experienced is testament to their effectiveness.

4. Close-up capabilities

#4: Close-up capabilities

Unique wide-angle macros when you shoot close to the subject

EOS R5/ RF10-20mm f/4L IS STM/ FL: 10mm/ Aperture-priority AE (f/4, 1/2500 sec, EV -0.7)/ ISO 200/ WB: 4900K

When you shoot at the 10mm end at the RF10-20mm f/4L IS STM’s 25cm closest focusing distance, you get wide-angle macro images with distinctive ultra-wide-angle distortion. It creates a surreal immersive feel, as though your surroundings are looming over you from within the frame.

This lens is Canon’s first RF mount L-series lens to use an STM (stepping motor), which contributes greatly to its smaller form factor. I found that focusing was smooth and seamless. It was reliable enough to allow me to concentrate on artistic aspects like composition, especially when combined with image stabilisation (up to 6 stops’ equivalent through Coordinated Control IS).

5. Angle of view

#5: Angle of view

At 10mm, I could capture the vast starry sky as it appeared to me

EOS R5/ RF10-20mm f/4L IS STM/ FL: 10mm/ Manual exposure (f/4, 10 sec, EV -0.7)/ ISO 6400/ WB: 3400K

Photographing the starry sky at 10mm is a splendid feeling—you can capture its vastness the way your bare eyes see it. Unlike a fisheye lens, the RF10-20mm f/4L IS STM is rectilinear, so the horizon doesn’t appear curved. This makes the resulting image more impactful.

10mm takes in much more of the scene than 14mm.

Image quality for astrophotography

Shooting at the maximum aperture at 10mm, the light fall-off (vignetting) at the image edges appears natural. Comatic aberration, which causes point light sources such as stars to appear comet-like, is well under control. I would use the maximum aperture without hesitation.

The idea of astrophotography at maximum aperture f/4 might sound incredulous to some photographers. However, the latest cameras have excellent high ISO speed performance. Moreover, even under the conservative 200 Rule, which astrophotography experts increasingly recommend over the 500 Rule when shooting higher resolution images, you can use an exposure of up to 20 (200/10) seconds to capture stars without trailing when shooting at 10mm. f/4 is sufficient.

Know this: Rear filter holder

Like its EF lens counterpart, the RF10-20mm f/4L IS STM’s protruding front element doesn’t take screw-in filters. However, it has a filter holder at the back that can take gelatine filters. This lets you insert a soft filter for astrophotography, which makes stars look bigger and brighter, or an ND filter if you shoot video. While you won’t be able to use a screw-in circular polariser (CPL), the lens’ colour rendering was so good that I didn’t feel disadvantaged.

In summary: A very well-balanced lens

In summary: A very well-balanced lens

With an ultra-wide-angle scope, outstanding image quality, image stabilisation, and high portability in the same package, the RF10-20mm f/4L IS STM isn’t just a revolutionary lens, it is also a very well-balanced one with excellent usability.

EOS R5 + RF10-20mm f/4L IS STM

 

Find out more about the RF10-20mm f/4L IS STM in:
RF10-20mm f/4L IS STM: The World’s Widest Non-Fisheye Zoom Lens
5 Key Elements to Developing the RF10-20mm f/4L IS STM

More landscape photography tips from Minefuyu Yamashita in:
Nailing the Shot: Moon and Milky Way Stars Over the Sea
One Location, Two Looks: Photographing a Lighthouse in Moonlight v.s Under the Stars
Shooting to Balance Colours: The Glittering Milky Way Over Greenery

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RF Lenses vs EF Lenses: What's the Difference and How to Decide?