Before the RF 24-105mm f/4L, Canon’s L lenses tended to use a Ring USM focusing motor for quick speed and high accuracy. However, what works for still photography doesn’t always translate to videography, which requires smooth and consistent focus movements rather than quick starts and stops.
Canon’s previous solution was the STM (Stepping Motor) autofocus technology, which provides the necessary smoothness and consistency for video recording, but always had slower focus speeds. That’s where Nano USM technology comes in! The Nano USM found on the Canon RF 24-105mm f/4L is accurate, smooth, and nearly silent. It also focuses almost instantaneously except in very dim conditions – the best of both worlds.
In manual focus, the RF 24-105mm f/4 also has very impressive performance. The manual focus ring is located beyond the zoom ring, which is my preferred position. It offers what is, to me, ideal resistance, and adjustments are very smooth. Note that Nano USM is a focus-by-wire manual focus design, which means that the manual focus ring electronically controls the lens’s focus. When the camera is off, for example, turning the focus ring does not do anything.
Finally, the Canon RF 24-105mm f/4 L has unusually good close focus capabilities for a non-macro lens. The maximum magnification of 0.24x (also written at 1:4.2 magnification) is enough to fill your photo with a subject just 15 centimeters wide (about 6 inches), assuming a full-frame camera. This isn’t quite macro photography, but it’s enough to allow some nice close-ups!
The Canon RF 24-105mm f/4L has impressive control over distortion, especially for a lens of this type. Wide-to-telephoto zooms commonly have at least 2-3% distortion on either end. Here’s how the Canon performs by comparison:
Not bad at all! By comparison, a similar lens like the Nikon Z 24-120mm f/4 S reaches -5.01% barrel distortion at the wide end and 3.89% pincushion distortion near the telephoto end.
In uncorrected images, the Canon RF 24-105mm f/4L manages vignetting reasonably well. The most you’ll see is about two stops of vignetting when shooting wide open at 24mm. As with the distortion, that’s better than usual for a midrange zoom – and it’s even more impressive when you consider that stopping down or zooming in slightly is enough to put the vignetting into negligible territory.
Here’s a full chart of vignetting levels at both close focus and infinity focus. Focus distance doesn’t affect vignetting too much on this lens, but I would note that the corners are about 1/2 stop darker if you’re at specifically 105mm, f/4, and infinity focus:
This vignetting is low enough that it will rarely present a problem. Even in the worst-case scenario of 24mm and f/4, software corrections will be able to remove the vignetting without leaving behind too much image noise in the corners.
Lateral Chromatic Aberration
There is a moderate amount of chromatic aberration on the Canon RF 24-105mm f/4L, although I didn’t measure it to be as high as what some other reviews online are saying. Here’s the chart as measured in Imatest:
The way we measure chromatic aberration, anything under about one pixel is hard to see in real-world images. While the Canon RF 24-105mm f/4L doesn’t reach that standard (except at 50mm and f/16 specifically), it’s never terrible, either. The performance from 24mm to 70mm doesn’t concern me at all – any CA at those apertures should be easy to remove in post-processing with one click. It’s a bit higher at 105mm, but even then, you should be able to apply corrections without leaving behind any major artifacts behind.
And now for the main event – how sharp is the Canon RF 24-105mm f/4L?
I definitely had high hopes for this lens considering how long Canon has spent refining the 24-105mm f/4 family of lenses, but I was left with a bit of a mixed bag. Before I share my thoughts, here’s how I measured this lens in the lab:
This lens is reasonably sharp at 24mm. It stays that way at 35mm, although the performance at 50mm dips a little, especially in the corners. By 70mm, we see a general decrease in sharpness wide-open, but stopping down to f/5.6 is enough to give good results across the frame. Unfortunately, the performance at 105mm is noticeably weaker, especially in the corners, which never get especially crispy even at their best aperture of f/11. Taking everything into account, it’s a sharp enough lens, but it won’t be breaking any records.
Midrange zooms are notoriously hard to design and often have mediocre sharpness, especially if you consider the ones made for DSLRs. However, some of the newest mirrorless zooms have taken big strides of improvement – and by that standard, the Canon RF 24-105mm f/4L looks like it’s falling a bit behind. It’s still sharp enough that any blurry photos with this lens will not be the lens’s fault, but it’s not at a high enough level to impress me, especially as you zoom in.
Note that there’s some wavy field curvature to this lens, especially at the wider focal lengths, which depresses the midframe sharpness numbers a bit. We always show our MTF charts with field curvature baked in, since it’s an accurate description of how your photos will look when everything in the scene is the same optical distance away (such as an overlook at infinity focus). Of course, real-world scenes vary, and you could get better or worse performance than this depending on the shape of the scene and your focusing distance. Field curvature does not always interact with the scene in a predictable manner.
I was happy to see that the Canon RF 24-105mm f/4L has almost no focus shift at all. This wasn’t necessarily a surprise on an f/4 lens, but it’s still welcome – it means that your focusing distance doesn’t change as you stop down to different aperture values.
Finally, something that videographers will strongly appreciate is that the Canon RF 24-105mm f/4L is essentially parfocal. In other words, the focusing distance changes very little as you zoom in or out. I still recommend that photographers re-focus the lens after changing the focal length significantly – it’s not perfectly parfocal – but this is better than 99% of zooms. Canon definitely looks out for their videographers.
Lenses of this type are not usually known for the quality of their bokeh, and the Canon RF 24-105mm f/4L IS USM turns in a mixed performance in this regard. Out-of-focus highlights are rendered circular in shape thanks to the 9 aperture blades, but the discs are relatively busy with some “onion ring” effect. The transition from in-focus to out-of-focus is also a little rough. That said, if you shoot at 105mm and f/4, and your subject is close enough, you can still isolate it pretty nicely.
Flare and Sunstars
Flare performance is a little better than expected on the Canon RF 24-105mm f/4L – it’s still on the high side, but for a complex midrange zoom, it’s hard to complain too much. The lens retains high levels of contrast when photographing against bright lights, and only if the bare sun is in your frame will you get a substantial flare pattern. This is the worst that you are likely to see in practice:
As for sunstars, the RF 24-105mm f/4L produces some nice 18-pointed stars because of the 9-bladed aperture diaphragm. That said, you’ll need to be at a narrow apertures of at least f/11 if you want such defined sunstars.
The next page of this review dives into the sharpness numbers a bit more, with some direct comparisons against other Canon mirrorless lenses. So, click the menu below to go to “Lens Comparisons”:
Table of Contents