It looks like Canon is finally responding to the need for budget-priced long telephotos - see below and here . The 100-500 mm has been officially announced and is expected to be released next month with the R5 (45 Mpx) and R6 (20 Mpx) mirrorless bodies. It should become the work-horse birding lens for the RF mirrorless mount. The two f/11 long telephotos are news and a bit of a surprise. Both are DO designs and patents published two years ago show they will be very light-weight and compact. The only down-side I see is that these are fair weather lenses. Don't worry about the IQ, it will be fine for all but the most demanding situations. The RF focal length multipliers are surely not for any of these lenses but for other telephotos yet to be announced, perhaps L-series f/4 or f/5.6 for the RF mount.

Canon RF 100-500mm f/4.5-7.1L IS USM
Canon RF 600mm f/11 DO IS STM
Canon RF 800mm f/11 DO IS STM
Canon RF 1.4x
Canon RF 2.0x

As an afterthought, I have attached recent measurements of the Spatial Frequency Response of the Canon 5Ds + 600 mm f/4 III at f/11. These measurements should be very close to the Canon R5 + RF 600 mm f/11. For reference, the Nyquist frequency which is the highest spatial frequency that can be resolved by the sensor, is 120.8 cycles/mm. Any higher frequencies present in the optical image will appear in the digital image as low frequency aliases. In this case the AA-filter has ensured any aliases will have negligible energy.

Correct me if I'm wrong but I think these lenses will only be useable on the Canon mirrorless cameras as I don't think there is an adapter to enable an RF mount lens to be used on a camera with an EF mount (that is, all the digital SLRs in the Canon range). There is certainly a mount adapter that goes the other way (EF lens on RF mount camera). I think the geometry makes the RF lens to EF camera adapter impossible?

Yes Glenn, you are absolutely correct. In addition to the points you raised, most DSLR bodies will not AF with a f/11 lens mounted. These lenses are RF lenses for mirrorless R-series bodies.

I have to admit to being a bit puzzled as to what train of thought lead Canon to these long, small aperture DO designs. My initial take on it would be something like: consumer-market research indicated a desire for very long focal length lenses; Canon decided to pursue DO designs for these to achieve the compactness wanted by the same market; it was then found necessary to restrict the maximum aperture to f/11 to achieve price points that would sell to that market.
Previous reports on the R series AF system indicate the resultant lenses should autofocus without problems at f/11, although whether the AF system will be at its sweet spot at that aperture may be a question. Also, as Ian has noted, they are lenses which will be at their best in bright, sunny conditions, which some users may find restrictive, particularly for bird/wildlife photography where high shutter speeds are necessary. A further issue may be the potential difficulty in avoiding background detail at f/11 depth of field. Personally I don't think I'm convinced at this point - it would have been more interesting to see designs with f/5.6 or f/8 maximum apertures.

The new f/11 lenses are a surprise. We need to see the total package R5 + RF f/11 DO in action to fully understand the role of this kind of kit. I will be very surprised if it turns out to be a 'dud'. Everything I see suggests this is a move to provide affordable long lenses for wildlife photographers to get them into the Canon ecosystem. Future long focal length f/5.6 and f/8 DO lenses will likely be L-series with a price tag like the 400 mm f/4 DO II.

Each to their own, of course, but I would never shell out what is likely to be at least a couple of grand on an f/11 lens. Ian politely describes this as a fair weather lens. However, its a full two stops slower than an f/5.6 lens, which is already on the slow side. Its a long time since I used anywhere near f/11 on any lens. (Ok, some cynics might say 'Yes, I noticed... ). I would even think twice about the 100-500 which goes to f/7.1, although I can see that at the right price this might appeal to the full frame market after a long zoom. For APSC, the 100-400 is good for most purposes, and is 2/3 stop better. The f/11 will be largely impractical for bird photography, in my view, unless you are prepared to put up with ISO3200 and above routinely. Not sure I can see who the obvious market group is for this sort of lens.

I fail to understand the logic behind going to smaller and smaller maximum apertures which then negate the benefits of sensor improvements, which Canon and Nikon now seem to be pursuing. Perhaps Canon hopes that the average consumer will look only at the big number (800) and ignore the small number (11) - isn't that the philosophy behind the average tiny sensor superzoom?

Simon