Canon RF 10-20mm F4L IS STM Comparison

Before you read what I’m writing here, I’ll just say one thing. If you love going really wide and even wider and have been waiting for your dream lens on the RF mount, then don’t waste time finishing reading this article before you preorder. Simply. Do. It. Now.

I remember a time when Canon’s ultra-wide lenses were their weakness as a matter of fact it was downright embarrassing, it was so bad we were adapting Nikon ultra wides onto our EF cameras. Now it seems Canon creates amazing super ultra wide lenses with bravado..Because only we can. I am critical of Canon a lot when they deserve it, but Canon certainly can create some of the best lenses in the world that others wouldn’t even attempt.

First, let’s compare the size of the comparable two lenses for the RF and EF mount from Canon

Canon RF 10-20mm F4L IS STM Canon EF 11-24mm F4L IS USM
Maximum Outer
Diameter x Length
3.3 in. x 4.4 in
83.7mm x112mm
4.3 in. x 5.2 in.
108.0 x 132.0mm
Weight 20.1 oz. / 1.3 lbs.
41.6 oz / 2.6 lbs

By taking advantage of the RF mount, Canon has managed to cut the weight in half and made the lens considerably smaller than the EF 11-24mm

image 12 - Canon RF 10-20mm F4L IS STM Comparison

Translated roughly: The Light Green elements are aspherical elements, the dark green elements are UD elements, and the olive-colored element is UD Aspherical. The red Square encapsulates the IS element.

As far as coatings, the Red dashes on the elements are SWC (Sub Wavelength Coating) coatings. The Dark blue/black dash is ASC or Air Sphere Coatings. Canon has placed multiple sub-wavelength coatings which are essentially nanoparticles to prevent flare and ghosting and also Air Sphere Coating, which looks like little nano balls deposited on the element surface.

The Canon EF 11-24mm was released before ASC and simply had the SWC coatings in similar element positions as the RF 10-20mm. So if you are happy with the flare response on the 11-22mm then you should be as equally happy if not more on the RF 10-20mm.

One thing I noticed missing from Canon’s information is a Fluorine Coating on the front element and rear elements. That coating isn’t responsible for optical quality but does help with dust, water droplets, etc getting on the exposed elements and makes the lens easier to clean.

The MTF’s

When Canon releases a lens like this the first thing I try to find and compare are the MTF (Modulation Transfer Function) charts. Canon’s MTFs are computed charts but give us an excellent first-hand judgment of the lens performance. However, charts can’t take into account the use of DLO and other functions that assist in improving lens performance. Canon’s latest charts also only include wide-open performance, and most lenses improve on their performance stopped down.

Canon has an excellent guide on how to read their MTF’s here.

image 15 - Canon RF 10-20mm F4L IS STM Comparison

Essentially, the lens is as good or better than the EF 11-24mm.

On the wide end, contrast is as good as the EF’s 11mm. Resolution is roughly on par between the two lenses, with again, the RF 10-20mm being a wider lens. On the long end, the bokeh should be improved over the EF 11-24mm, the contrast the same, and the resolution does not appear to show a noticeable difference.

Of course, this depends on QC, and a multitude of factors, but also given this lens is much smaller, lighter, and cheaper, and wider – being as good or better is certainly a win.

Preorder from B&H Photo for $2299.

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