A Review of the Canon RF 10-20mm for Underwater Photographers & Videographers

By Bill Hawthorne

The Canon RF 10-20mm f/4 ultra-wide zoom is an incredibly sharp, fast, lightweight, and frankly darn cool lens. I have been waiting for an ultra-wide rectilinear RF lens since I first heard rumors a couple years ago. When Canon finally announced the RF 10-20mm f/4 L IS STM lens on October 11, 2023, I was immediately very excited about the concept and eager to test it underwater. As one of the widest rectilinear lenses available, I thought it would have great potential for underwater photographers and videographers. I have been testing this lens since mid-March. Since then, I have taken over 3,000 pictures and dozens of videos with the lens, using it for wide-angle shots and portraits both above and below water. I believe this is the ultimate rectilinear lens, but does this mean it’s the best underwater option? In this review, I discuss my experience using this lens underwater with the goal of aiding in the decision of whether it is a good lens for you.

The focus speed on this lens is incredibly fast and perfectly silent. 10mm • 1/60 • f/18 • ISO 640. © Bill Hawthorne

Attributes

When I opened the box and held this lens in my hand, my very first thought was “wow, it’s small”. The lens weighs 1.3 lbs and is approximately 3.3” x 4.4”. When attached to the camera, it feels incredibly natural to move around. The size doesn’t matter much in a housing, but any opportunity to decrease the weight is always appreciated.

I used this lens behind both the Ikelite DL 8in dome port and the DL Compact 8in dome port. I found the lens performed similar behind both ports; of course it was slightly sharper behind the full size 8in port, but I preferred the DL Compact 8in for its small size and weight. As with any wide-angle rectilinear lens, it definitely struggled with edge performance behind a dome port. I consistently found myself closing down the aperture to around f/16 to have reasonable sharpness around the edges. This isn’t unexpected at all for a rectilinear lens behind a dome port, especially such a wide lens, but it is an important thing to keep in mind. It is also important to mention that there is not an alternative flat port option for this lens. Flat ports can reduce the effective angle of the image and vignette very badly; at this point, dome ports are the best option for ultra-wide lenses. Unfortunately, the curved port also creates a fair amount of distortion around the edges that make the image look stretched. This is minimized when you zoom in but what’s the point of having this lens if you can’t use it at 10mm?

This lens is exceptionally well-suited for capturing aquascapes. 20mm • 1/30 • f/16 • ISO 3200 © Bill Hawthorne

The focus speed on this lens is incredibly fast and perfectly silent. I had no issues focusing in very low light and never noticed any hunting issues even in turbid waters.

I love the 10-20mm zoom range. You can take great wide-angle shots or zoom in for portraits and subjects further away. I usually only shoot wide angle, but I constantly found myself changing around the zoom for a variety of different shooting styles. Being able to adapt to different scenarios underwater is a huge benefit and, in my opinion, this lens boasts the perfect zoom range.

I usually only shoot wide angle, but I constantly found myself changing around the zoom for a variety of different shooting styles.. in my opinion, this lens boasts the perfect zoom range. 20mm • 1/60s • f/13 • ISO 1250 © Bill Hawthorne

Application

I had a very fun time shooting this lens. Shooting such a wide rectilinear lens had some challenges but it opened fun opportunities for new shooting styles. The zoom range and small size makes this lens very applicable to a wide variety of scenarios. I tried using this lens for wide angle scenery shots, split shots, close focus wide angle (my personal favorite), and a variety of videography styles. While it excelled in some styles, it is definitely not meant for others.

This lens is fantastic for split shots... the rectilinear nature retains natural lines and shapes. This is very important when shooting subjects that have a very recognizable lines like piers or trees. 12mm • 1/60s • f/13 • ISO 640 © Bill Hawthorne

I believe this lens is best built for wide angle scenic shots. The wide angle and rectilinear nature allow for the capture of beautiful scenes with a realistic look. Its unique combination of ultra-wide-angle capabilities as a rectilinear lens makes it exceptionally well-suited for capturing aquascapes; ensuring photographs preserve the true proportions and perspectives of the natural environment. As such, this lens is well suited to shooting pelagics, big animals, and models, where lack of distortion is a plus and edge sharpness isn’t usually a big issue.

A beautifully vegetated Florida spring captured through the 10-20mm lens. Shot at 10mm • 1/30s • f/14 • ISO 640. Shot on a Canon R6, Ikelite housing, and 8in dome port with dual DS232 strobes. © Bill Hawthorne

This lens is fantastic for split shots. It is wide enough to capture dramatic scenes. When shooting on a fisheye lens, I love the distortion underwater but hate the above water distortion. This lens is a fantastic solution as the rectilinear nature retains natural lines and shapes. This is very important when shooting subjects that have a very recognizable lines like piers or trees.

A split shot of a researcher during a turtle survey. Note the level horizon and straight trees. Shot at 14mm • 1/80s • f/18 • ISO 500 on a Canon R6, Ikelite housing, and Ikelite 8in dome port with dual DS232 strobes.

I love close focus wide angle; I do not love this lens for close focus wide angle. When compared to my preferred fisheye lens (Canon EF 8-15mm f/4), I really miss the distortion which emphasizes the subject against the background. The 10-20mm can obtain a maximum magnification of 0.12x at 20mm and 0.06x at 10mm, and focuses at a minimum of 9.8inches (25cm) which is not quite as short as my fisheye lens (6.2 inches / 16 cm). For close focus wide angle, the difference between a few inches can make a very large difference. I wouldn’t even think about trying to photograph small subjects with this lens but that’s not what it’s designed for anyways.

Fisheye lenses distort the image, making subjects look larger and closer. This is great in some scenarios and not so great in others. Rectilinear shot at 14mm, 1/80s, f/18, ISO 500. Fisheye shot at 14mm, 1/8s, f/14, and ISO 200. Both photographs shot on a Canon R6, Ikelite housing, and Ikelite 8in dome port with dual DS232 strobes.

I really enjoyed this lens for videography. In my opinion rectilinear looks much better for video and the image stabilization is fantastic (especially when paired with the in-body image stabilization of my R6). It gives nice smooth video even in shaky conditions like high flow rivers or trying to hold the camera high for split shots. As most videographers tend to stick with rectilinear lenses, I believe this lens is one of the best options available for videography.

SEE MORE: Detailed Edge Sharpness Comparison to Canon EF 8-15mm Fisheye 

A comparison of edge performance between the EF 8-15mm fisheye and RF 10-20mm rectilinear. The RF lens handles open apertures poorly and has a fair amount of distortion. See the full-size images

Summary

The Canon RF 10-20mm f/4 ultra-wide zoom lens offers a compact and lightweight option for underwater photographers and videographers. With its versatile zoom range and fast, silent autofocus, it presents exciting opportunities for new shooting styles. However, its edge sharpness and distortion may disappoint some shooters. Despite this drawback, the lens excels in capturing wide angle scenic shots and split shots, where its rectilinear nature keeps the image looking natural. Its suitability for videography, with impressive image stabilization and autofocus, makes it a great choice for underwater filmmaking. Overall, while not without its tradeoffs, the Canon RF 10-20mm lens offers a fantastic option for those seeking versatility and rectilinear shooting.

The Canon RF 10-20mm lens offers a fantastic option for those seeking versatility and rectilinear shooting. 10mm • 1/40s • f/18 • ISO 640 © Bill Hawthorne

Additional Reading

Rectilinear vs Fisheye Lenses for Underwater Wide Angle Photography [VIDEO]

The Best Canon RF-Mount Lenses for DLM Underwater Housings

Canon EOS R6 Underwater Photos and Review

Ikelite DS232 Strobe Features // The ULTIMATE Strobe with Video Light All-In-One [VIDEO]

Close Focus Wide Angle In Depth

What Secrets Lurk Underwater in the Florida Springs at Night?

Bill Hawthorne is an aquatic ecologist specializing in the study of the freshwater springs of Florida. Bill focuses his studies and photography on freshwater species, most notably turtles. By sharing his underwater images, Bill hopes he'll expand his viewers' passion toward these unique environments and animals. Check out more of his work on his website, Instagram @billhawthornephotography, TikTok, and YouTube.