Ultra-wide-angle lenses are a must-have for photographing vast landscapes. Is the RF10-20mm f/4L IS STM a worthy addition to your lens collection? Landscape photographer Takashi Karaki compares it to his existing RF15-35mm f/2.8L IS USM. (Reported by: Takashi Karaki, Digital Camera Magazine)

 

Checkpoint #1: Does 5mm wider make that much of a difference?

When shooting in the wide-angle range (below 35mm), even 1mm makes a big difference to the field of view. The field of view is 130° at 10mm, 20° more than the 110° you get at 15mm.

I’ve shot scenic views all over Japan, and many locations require an ultra-wide-angle lens for maximum impact. Space to move back is usually limited, too. I’ve been “saved” by the RF10-20mm f/4L IS STM’s 10mm end countless times!

Shot from the same position

I wanted to capture as much of the 11km-long Seto Ohashi Bridge in the frame as possible. At 15mm, cropping off the right side of the bridge is inevitable, whereas 10mm easily fits it in. The sense of visual perspective is also stronger at 10mm: you can see how the bridge stretches dynamically from the foreground into the distance.

Shot at the closest focusing distance

At 15mm, you can get an impactful close-up of the ice but not much of the sky. 10mm allows the beautiful ombre sky to be included in the frame, too.

 

Checkpoint #2: Star photography without trailing

A larger maximum aperture makes it easier to capture starscapes with pinpoint stars especially in dark locations such as mountain peaks and by the Hokkaido seaside. You can shoot with a shorter exposure to avoid trailing.

While the RF15-35mm f/2.8L IS USM’s 1-stop advantage over the RF10-20mm f/4L IS STM’s f/4 maximum aperture may not seem like much, it halves the exposure time required to get the same brightness. For example, a 30-second exposure at f/2.8 would require a 60-second exposure to achieve the same brightness at f/4: too long to avoid trailing.

EOS R5/ RF15-35mm f/2.8L IS USM/ FL: 15mm/ Manual exposure (f/2.8, 30 sec)/ ISO 4000/ WB: 3,500K

 

Checkpoint #3: Corner image quality at the wide-angle end

Corner image quality is always a concern when shooting with wide-angle lenses. There may be vignetting or peripheral blurring depending on the lens design, and they can be particularly visible in certain types of shots. I’m extra wary of them when I’m shooting the sky from a mountaintop, or when I want to place mountain ridges in the corners.

Both the RF15-35mm f/2.8L IS USM and the RF10-20mm f/4L IS STM have aspherical lens elements that correct distortion aberration. Both also use new optical technologies that deliver excellent image quality over the entire image. However, when comparing images shot under the same conditions, I feel that the RF15-35mm f/2.8L IS USM seems to provide slightly better optical quality.

RF10-20mm f/4L IS STM

RF15-35mm f/2.8L IS USM

Left corner

Right corner

Notice the blurring and loss of detail in the corners of the image shot on the RF10-20mm f/4L IS STM, especially in the edges of the flowers. Details are sharper in the RF15-35mm f/2.8L IS USM image.

 

Checkpoint #4: Backlight performance

What’s landscape photography without shooting in dramatic backlighting? Both the RF15-35mm f/2.8L IS USM and the RF10-20mm f/4L IS STM are designed to provide impeccable image quality even in backlight. They have two different special anti-reflective coatings to reduce ghosting and flaring:

- SWC (Subwavelength Structure Coating): Prevents secondary reflection by smoothening the path of light entering the lens at high angles of incidence.
- ASC (Air Sphere Coating): Prevents reflection of light that enters at small angles of incidence (nearly perpendicular to the lens)

However, these do not eliminate ghosting and flaring completely. From my personal experience, ghosting and flaring are visible in my images shot about 10 minutes after sunrise, and 10 minutes before sunset. The RF10-20mm f/4L IS STM also seems slightly more susceptible to ghosting and flaring in backlight, probably due to its protruding front element. However, that can be easily managed and shouldn’t stop you from shooting in backlight.

RF10-20mm f/4L IS STM

EOS R5/ RF10-20mm f/4L IS STM/ FL: 10mm/ Manual exposure (f/7.1, 1/640 sec)/ ISO 320

The light from the setting sun was rather intense in this shot, which made me worried about ghosting and flaring. Luckily, it isn’t obvious, and the dramatic lighting and panoramic 10mm angle of view worked together to create a stunning evening snowscape.

RF15-35mm f/2.8L IS USM

EOS R5/ RF15-35mm f/2.8L IS USM/ FL: 15mm/ Manual exposure (f/13, 1/800 sec)/ ISO 800

“Diamond Daisen”—the sun rising like a shining diamond right above the peak of Mount Daisen, the highest mountain in the Chugoku region. The strong morning sun was shining directly into the lens, but the resulting image was clean and clear. The details in the clouds were also beautifully captured.

 

Photographer’s pick: RF10-20mm f/4L IS STM*

*Note: this is the author’s opinion

I love using my RF15-35mm f/2.8L IS USM, but was excited by the release of the RF10-20mm f/4L IS STM,  the world’s first full-frame non-fisheye autofocus-supported wide-angle zoom lens starting at 10mm. There was a lot I was curious about: the kind of possibilities provided by that extra 5mm scope, the image quality at the corners, and whether the f/4 maximum aperture would be a disadvantage. I addressed those questions when I compared the lenses.

Although the RF15-35mm f/2.8L IS USM performs slightly better than the RF10-20mm f/4L IS STM,  I feel that the RF10-20mm f/4L IS STM is still an excellent addition to a landscape photographer’s kit.  At 10mm, it delivers unparallelled natural-looking images with barely any visible (unwanted) distortion aberration. It's no exaggeration to say the lens has shown me new ways to see the world, expanding my vision and creative possibilities!

This doesn’t mean I’m letting go of my trusty RF15-35mm f/2.8L IS USM. The f/2.8 maximum aperture provides a firm advantage for night photography, and I like how I can use a screw-in PL filter in front.

Recommendations for users
If you are getting your first ultra-wide-angle lens, consider getting the RF10-20mm f/4L IS STM first. You can add the RF15-35mm f/2.8L IS USM later if you think you need it.

 

Composition tip: 10mm is excellent for showcasing background details even in close-ups

 

Learn more about the RF10-20mm f/4L IS STM and RF15-35mm f/2.8L IS USM in:
Expand Your Travel Vision with Wide-angle Zoom Lenses
Lens Review: RF15-35mm f/2.8L IS USM in Landscape Photography
Lens Review: RF10-20mm f/4L IS STM in Ocean Landscapes
5 Key Elements to Developing the RF10-20mm f/4L IS STM

More insights and landscape photography tips from Takashi Karaki in:
Landscape Photography Technique: Snowy Mountain in the Moonlight
3-minute Post-Processing: Sunbeams at a Waterfall
Getting Started in Landscape Photography: 5 Things to Know
Lighting in Landscape Photography (2): Underexposing for Drama