21 May 2023

The Lenses

In 2020 and 2021, Canon caused a stir with its RF 600 mm f/11, RF 800 mm f/11, and RF 100-500 f/5.6-8 lenses, which are much lighter and cheaper than EF lenses with similar focal lengths.

Of course, they were also much slower. The primes have a fixed aperture of f/11 and the zoom is f/8 at its long end, whereas earlier EF lenses all had apertures of f/5.6 or faster. This change was made possible by the dual-pixel autofocus system in RF bodies, which can focus at slower apertures than the conventional phase-detection systems in EF bodies.

These lenses truly represented a new possibility for full-frame RF bodies. With full-frame EF DSLRs, these focal lengths had required expensive and heavy f/5.6 or faster lenses. Now, a full-frame RF body could achieve long focal lengths with much lighter and less expensive lenses.

Compared to Other Lenses

That said, I’ll make the point that crop-sensor bodies have been enjoying similar lenses for years. Let’s consider these long lenses, all available for under $1500 new:

I’m limiting myself to lenses that are similar in price to the RF lenses. We can argue about whether a $1300 lens is similar in price to a $800 lens, but excluding these slightly more expensive lenses would not change the conclusions of this discussion.

Now let’s consider their equivalent aperture at an equivalent focal length of 600 mm on FF, APS-C, and MFT sensors as appropriate. The equivalent aperture gives us a means to directly compare the light-gathering capability of lenses used with different sensor sizes. I’m choosing 600 mm as a typical equivalent focal length for wildlife photography and also to directly match the RF 600 mm f/11.

The equivalent aperture is calculated taking into account the crop factor of the sensor. For example, consider the Sigma 100-400 mm on Canon APS-C with a crop factor of 1.6×. To reach an equivalent focal length of 600 mm, we need an actual focal length of 400/1.6 mm = 375 mm. At this actual focal length, the actual aperture is f/6.3 and the equivalent aperture is 6.3 × 1.6 = 10.

The bar chart shows the results. Click for a larger version.

Equivalent Aperture at 600 mm Equivalent Focal Length.

We can see that, with the exception of the heavier Sigma and Tamron 150-600 mm lenses, all of the lenses have very similar equivalent apertures between f/14 and f/10. The RF 600 mm f/11 is towards the faster end of this range and the RF 100-400 f/5.6-8 is towards the slower end. Again, with the exception of the 150-600 mm lenses, the other lenses are lighter or similar in weight to the RF 600 mm f/11 and many are similar in weight to the RF 100-400 mm f/5.6-8.

The 150-600 mm lenses are about ½ a stop faster on APS-C (f/9) and about 1½ stops faster on full-frame (f/6.3). They are also about twice as heavy as the RF 600 mm f/11 and three times as heavy as the RF 100-400 f/5.6-8.

Of course, cost, weight, and aperture are not the only important characteristics of long lenses. Minimally, one also needs to consider sharpness and focus speed. That said, there are lenses here that are very competitive in these areas, especially the Fuji, Sony, and Sigma lenses and the more expensive Olympus and Panasonic 100-400 mm lenses.


The slow RF telephotos, the RF 600 mm f/11, RF 800 mm f/11, and RF 100-400 mm f/5.6-8, are useful lenses for full-frame RF users who want to have light, relatively cheap lenses. However, they give capabilities that are similar to those that have been available for APS-C and MFT users for many years. This is not a bad thing, in that it allows a full-frame RF user flexibility to choose either a light/cheap/slow lens or a heavy/expensive/fast long lens.

I’d also note that the Sigma 100-400 f/5-6.3 and Sigma 150-600 mm f/5-6.3 are no more expensive than the RF 100-400 f/5-6.3 and RF 600 mm f/11 and are significantly faster. This speed comes at a cost in weight, of course. They are definitely worth considering adapting to an RF body.