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Imaging resource had a chance to sit down with Canon engineers to discuss the development of the brand new Canon EOS system.
We cherry-picked a couple of our favourite questions and answers from the interview.
Does AF coverage change with EF-mount lenses?
Since EF-mount lenses used via the adapter are so much further from the sensor surface, it seems likely that they wouldn’t be able to support as large an AF area as native RF-mount ones. I asked, and it turns out this is true. It will vary some based on the specific lens design, but some EF-mount lenses won’t have quite as wide AF coverage as the native ones. Native RF-mount coverage is 100% vertically and 88% horizontally, but some EF-mount lenses will only have 80% horizontal coverage (again, depending on the specific lens design).
Why so many electrical contacts? (In regards to the RF mount)
The engineers didn’t go into a lot of depth about what sorts of functions needed the increased bandwidth, but one example they gave was that every R-series lens carries a complete set of distortion-, aberration- and diffraction-correction information in an internal memory. All that data gets dumped to the body every time you attach an R-series lens to a body, so it’s important to have it happen quickly.
Another use is for the real-time focus-distance information display in the viewfinder. I didn’t play with this very much, but it seemed to be extremely responsive to changes in subject distance.
Finally, it turns out that the aperture setting in EOS R lenses can be updated more rapidly (and in steps of just 1/8 EV, vs. the 1/3 EV of EF-series optics). More steps and faster updates benefit from a higher-bandwidth camera/lens connection.
4K video specs, why not better?
When I asked the engineers why the limitations in 4K, their reply was a bit cryptic, mentioning the “CMOS sensor system”. A little might have been lost in translation, but I think what it boils down to is that Canon may not yet have the technology to enable full-frame/no-crop 4K readout from their chips.
As noted earlier, this is, in fact, the same sensor as in the 5D Mark IV, so it’s two-year-old technology at this point. Looking at Canon’s other products, the slightly older 1D X Mark II only has a 1.3x crop factor, but it’s also only a 20 megapixel sensor. Even the top-of-the-line Cinema EOS C700 camera’s sensor isn’t a full-frame 35mm, but rather a little larger than the “Super 35” format. So, looking across their line, it looks like 4K readout across a full 35mm frame is an issue for them.
As noted, though, the good news is that the EOS R isn’t merely as capable as the 5D IV in doing 4K video, but it has a much-improved codec to trim file sizes at the same relative quality as well. Read the full interview
You can preorder the new Canon EOS R camera and lenses through Adorama, our exclusive affiliate partner.