Canon RF 85mm f/2 STM IS macro - Review / Test Report - Analysis
Lens Reviews - Canon EOS (Full Format)

Distortion

85mm lenses tend to be rather simple beings in terms of optical design so it doesn't come as a surprise that image distortions remain very moderate at just 1.1% (pincushion) in RAW files. That's slightly higher than on true macro lenses though. Of course, image auto-correction can eliminate these traces so it's usually nothing to worry about anyway.

Vignetting

The vignetting characteristic is typical for a lens in this speed class. RAW images show a substantial degree (2 f-stops) of light falloff at f/2. The issue is very much reduced at f/2.8 and basically gone from f/4 onward.

Activated auto-correction is fairly aggressive with a 1.5 f-stop gain at f/2 - and the corresponding increase in sensor noise in the corners. The correction is much less pronounced at smaller aperture settings, of course.

MTF (resolution) at 45 megapixels

The resolution of the Canon RF 85mm f/2 STM IS macro is very impressive straight from its maximum aperture setting. The broader center is already excellent at f/2 and the borders/corners are very good. Stopping down to f/2.8 provides an extra boost. The peak quality is reached at f/4 with an excellent quality across the entire image field. Diffraction has a slight impact between f/5.6 and f/11. A more pronounced drop starts at f/16 where the resolution hovers around good to very good marks. We wouldn't really recommend stopping down beyond f/16 unless you have a lower megapixel camera.

The centering quality of the tested sample was good. The field curvature is low.

Please note that the MTF results are not directly comparable across the different systems!

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

Lateral CAs have an average width around 0.3px at the image borders. This is negligible.

Bokeh

Given the large max aperture and macro capabilities, the quality of the bokeh will be an interesting aspect for most users.

Out-of-focus highlights are nicely rendered. The discs have a very smooth inner zone and there's basically no outlining effect. The circular disc shape is maintained from f/2 to f/4 which is better than on most lenses.

The above is true for the image center. As so often the circular disc shape deteriorates to cat eyes in the image corners. This starts fairly "early" at f/2. The "circular shape" zone broadens substantially at f/2.8 and the outer discs are almost fully corrected at f/4.

As far as the general blur is concerned, there are two flavors to discuss here. The foreground blur (shown to the right below) is very smooth and buttery whereas the background blur (to the left) exposes some hard edges at high contrast transitions. This is also something that you may observe in some of the provided sample images.

Bokeh Fringing

In a perfect world scenario, you won’t see any axial CAs thus color fringing on the Z-axis. However, only a handful of fast lenses are correcting the issue effectively - and the RF 85mm f/2 STM IS macro is not among them. You should be able to spot a significant amount of purplish fringing in the foreground and a greenish tint beyond the focus point. The effect is reduced at f/2.8 and minor traces remain visible at f/4.