It’s here, Canon RF 100-300mm f/2.8L IS USM officially announced

Because the rear elements would then be inside the mount and might even block the mirror path. Sorry, I don't have the time to start measuring if the latter would be the case.
I didn't say that a 100-500 mm wouldn't be possible, what I meant is that the actual design of the RF 100-500 mm would not have been possible in the EF mount.
I don't think anyone is suggesting that the exact same RF design could have been used for the EF mount. Obviously the backfocus distance precludes that. But in general, the telephoto designs for RF could easily have analogous designs in the EF mount. In the case of the RF 100-500, what really makes that lens possible is that MILCs don't need f/5.6 to focus – as has been pointed out many times, 500/7.1 and 400/5.6 have the essentially the same physical aperture.

As I suggested previously, and @AlanF just stated, the main benefits of a shorter flange distance are realized with wide and normal focal lengths.
 
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I think the advantages of the RF mount are primarily with short focal length lenses rather than telephotos since their inherent focal lengths are greater than the flange-sensor distance. I don't understand some of Canon's design choices. The one substantive gripe about the RF 100-500mm is that the rear element of the lens retracts so close that the TCs fit only for a 300mm or greater setting, and they didn't have this problem when the lens was even further from the sensor with the EF mount. They have overcome this problem for the RF 100-300mm, but that has upset those who use drop-in filters (which I don't). I don't think these problems are due to any limitations of the RF mount but the designers making compromises for reasons they haven't explained or simply they cocked up.
It puzzles me that Canon, Nikon and Sony choose to make (MILC) extenders that protrude deep into the barrel of the lens they are attached to.

I'd guess that the reason why the real element of the RF100-500mm is too close to allow extenders at less than the 300mm setting, is a deliberate choice - I don't think their designers would "penis-up" - they would have cost and size constraints imposed on them by the marketing dept. It may have been necessary in order to produce a high performance compact extending zoom.

Also feasible it was at least partly for marketing segmentation reasons - if a 1.4x extender allowed 140-700 it would cannibalise sales of a potential 200-600 (the latter is notably absent from Canon's range, and one of the main reasons quoted to me by Sony birders who use their 200-600).

I don't know whether Sony extenders impose similar minimum focal length restrictions, but the fact that they produce an excellent and affordable 200-600 makes it a moot point anyway.
 
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The 600 and 800 f/11 primes are another example of something just not possible on EF Mount (same reason, no AF) that is bringing great IQ at previously inaccessible focal lengths to the consumer AND at a ridiculously high AF keeper rate.
That's nothing to do with the mount, it is because AF is on the sensor - using DPAF, they can focus at f/11 and narrower. I used to focus EF lenses on the 5DIV at apertures narrower than f/8 using stacked TCs or a 3x Kenko TC with Liveview, which uses DPAF on the sensor. It's being mirrorless that is important for the improved AF.
 
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It puzzles me that Canon, Nikon and Sony choose to make (MILC) extenders that protrude deep into the barrel of the lens they are attached to.

I'd guess that the reason why the real element of the RF100-500mm is too close to allow extenders at less than the 300mm setting, is a deliberate choice - I don't think their designers would "penis-up" - they would have cost and size constraints imposed on them by the marketing dept. It may have been necessary in order to produce a high performance compact extending zoom.

Also feasible it was at least partly for marketing segmentation reasons - if a 1.4x extender allowed 140-700 it would cannibalise sales of a potential 200-600 (the latter is notably absent from Canon's range, and one of the main reasons quoted to me by Sony birders who use their 200-600).

I don't know whether Sony extenders impose similar minimum focal length restrictions, but the fact that they produce an excellent and affordable 200-600 makes it a moot point anyway.
The problem is that Canon hasn't explained why so we can only guess. I would have thought the segmentation theory unlikely. My pet theory for a "penis-up" (presented on CR years ago) is that RF TC design team and the RF lens team failed to communicate! There is an opportunity for 3rd party extenders here that do not extend into the lens, which would give the complete zoom range. If they made such extenders which just had the communicating wires going from the front to the back without attempting to report back on the change of f-number, then they need not reverse engineer any communication protocols. My first-generation 3x Kenko does this, and always worked, and I just had to note the f/number was 3x greater than reported on the EXIF. Kenko then got clever and put in a chip to report the true aperture. Canon changed their protocols, which then killed the Kenco TC.
 
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I don't think anyone is suggesting that the exact same RF design could have been used for the EF mount. Obviously the backfocus distance precludes that. But in general, the telephoto designs for RF could easily have analogous designs in the EF mount. In the case of the RF 100-500, what really makes that lens possible is that MILCs don't need f/5.6 to focus – as has been pointed out many times, 500/7.1 and 400/5.6 have the essentially the same physical aperture.

As I suggested previously, and @AlanF just stated, the main benefits of a shorter flange distance are realized with wide and normal focal lengths.
Agreed, but that was a reply to a comment referring to a specific sentence in an earlier post. And the original post was about the RF mount having limitations, which is not the case.
 
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The problem is that Canon hasn't explained why so we can only guess. I would have thought the segmentation theory unlikely. My pet theory for a "penis-up" (presented on CR years ago) is that RF TC design team and the RF lens team failed to communicate! There is an opportunity for 3rd party extenders here that do not extend into the lens, which would give the complete zoom range. If they made such extenders which just had the communicating wires going from the front to the back without attempting to report back on the change of f-number, then they need not reverse engineer any communication protocols. My first-generation 3x Kenko does this, and always worked, and I just had to note the f/number was 3x greater than reported on the EXIF. Kenko then got clever and put in a chip to report the true aperture. Canon changed their protocols, which then killed the Kenco TC.
I believe it was Canon’s intent in designing the TCs that they are only compatible with certain lenses. You can stick a non-protruding TC behind a 24-105 if you want, but Canon doesn’t want you doing that with their TCs, they want you to buy the 70-200 instead. That was true for EF, it’s as true for RF.

I don’t believe it was unintentional, but rather a marketing-driven choice.
 
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Agreed, but that was a reply to a comment referring to a specific sentence in an earlier post. And the original post was about the RF mount having limitations, which is not the case.
Lol. Of course the RF mount imposes limitations. They’re not the same as the limitations imposed by the EF mount, but they are certainly present.

And no, the post to which you initially replied simply stated that lenses such as an extending 70-200, a 100-500 and a 100-300/2.8 could have been designed for the EF mount. That’s absolutely true. They wouldn’t have been the RF designs, of course.

I do agree that the things like the the 100-500 extender partial incompatibility and elimination of the drop-in filter slot from the 100-300 are not due to the RF mount directly, but rather design choices made by Canon for those lenses. Worth noting that the EF 70-300L had the same characteristic as the RF 100-500, it worked with TCs but only from 250-300mm.
 
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I believe it was Canon’s intent in designing the TCs that they are only compatible with certain lenses. You can stick a non-protruding TC behind a 24-105 if you want, but Canon doesn’t want you doing that with their TCs, they want you to buy the 70-200 instead. That was true for EF, it’s as true for RF.

I don’t believe it was unintentional, but rather a marketing-driven choice.
If true, then what so and sos they are. I really hope that 3rd party extenders will appear. The RF 100-400 is full compatible with the TCs.
 
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The Canon store in South Melbourne have a production unit in store until the end of next week. It feels nicely balanced on the R3 and focus acquisition is very fast. Like the 70-200, the zoom throw is a bit long to go through the whole range without adjusting your grip though.
 
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I don't think anyone is suggesting that the exact same RF design could have been used for the EF mount. Obviously the backfocus distance precludes that. But in general, the telephoto designs for RF could easily have analogous designs in the EF mount. In the case of the RF 100-500, what really makes that lens possible is that MILCs don't need f/5.6 to focus – as has been pointed out many times, 500/7.1 and 400/5.6 have the essentially the same physical aperture.

As I suggested previously, and @AlanF just stated, the main benefits of a shorter flange distance are realized with wide and normal focal lengths.
A shorter flange distance is a huge advantage no leica M owner will deny!
 
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If true, then what so and sos they are. I really hope that 3rd party extenders will appear. The RF 100-400 is full compatible with the TCs.
Why else make them that way? They could have made the barrel longer in front, putting it even with the extended optics.

For EF, ‘official’ compatibility was restricted to L lenses 135mm or longer. When the 70-300L came out, it was listed as incompatible with the extenders, but that changed ‘officially’ with the 1D X firmware update that enabled f/8 AF, when the 1.4x was listed as compatible (even though it was not reported to the body, since the lens lacks the three extra pinouts).
 
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maybe it's simply because the USA is a big and rich country and they sell more lenses, tool sets or drills there, so they just need a smaller margin per piece.

It's cheaper to do business in the USA. Everything from no consumer protections to the cost of hiring workers (at all levels from the guys working at the port through Nikon USA to the camera shops) is much cheaper. No pesky benefits paid to many people, no socialized healthcare that companies have to help fund, that sort of thing.
 
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I just have to be honest and voice my overwhelming disappointment with this lens. The lack of rear filters makes this lens dead on arrival to me without any question at all. With all the greatness of versatility this brings to the table as a high quality zoom, it's totally useless to me now because it lacks rear filters - something I use every single moment of daylight as a motorsports photographer.

I, like many others that use these big primes, like to shoot with a CPL or ND filter in order to creatively use aperture and shutter speed to blur motion or alter reflections in cars. I've honestly never used my EF 300mm f/2.8L II during the day without at least some kind of filter in mine. This is a MAJOR oversight and makes this entire generation of lens useless to me. I now have zero upgrade path at all with the RF system to replace my EF 300L because I honestly can't and won't use this lens ever, nor do I want to. I have no intention of purchasing and traveling with a new set of 120mm filters, removing the hood every time I need to adjust the polarizer, or handling massive filters in the field in adverse conditions, figuring out how to store and transport them around a track or through the desert, etc. This lens is also MASSIVE and heavier compared to the old EF Mark II model which I find a large negative as well....since I have to pack and travel with this lens every month. I can understand this tradeoff for the obvious benefits and introduction of zoom functionality, but it's just another attribute that I view as a negative.

This is my personal perspective looking at this lens and considering how I use my current 300mm lens or all of my other lenses for that matter. I believe this is a major blunder and design oversight. Looks like I'll be hanging onto my EF 300 f/2.8L II for a long time and I will never rent or buy this lens because it's just totally useless to me because of this.
Just looked at your site, and you have excellent work. I especially appreciated your opening image from turn one at Sebring at dusk. I was the track photographer for the 12 hour race in 2016, and I know that image is so important. I am curious about your usage of a CPL filter with cars, especially panning. As a car passes by your position, the reflections move about, plus with the use of multiple tear off front windshield screens on most race cars, they can create additional problems. I have found opening up these areas of the car in post works pretty well. Lastly, using a CPL on a stationary car, reveals too much of the interior (roll cage, etc) which I find distracting. This new lens is primarily designed for indoor sports, and it will have great sales just for that. BTW, for the 1960 Olympics in Toyko, Nikon produced a handful of 300mm F2.0 lenses. I can't imagine shooting with that manual focus monster and pushing ISO 400 film as well.
 
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Lol. Of course the RF mount imposes limitations. They’re not the same as the limitations imposed by the EF mount, but they are certainly present.
Sure, but what are the tradeoffs Canon has to make in lens design to accommodate the limitations of the RF mount? The design choices made for RF lenses are choices, they are not imposed by the RF mount. The RF mount does not make it impossible to design a 70-200 or 100-500 compatible with TCs. Of course the RF mount has some limitations, but it gives more design freedom than the EF mount. But yeah, I agree that I should re-read my posts one more time before posting as my last reply might have implied that the RF mount does not impose any limitation, which is obviously not the case and is not what I meant...
And no, the post to which you initially replied simply stated that lenses such as an extending 70-200, a 100-500 and a 100-300/2.8 could have been designed for the EF mount. That’s absolutely true. They wouldn’t have been the RF designs, of course.
Correct, but likely with other disadvantages like bulk and weight compared to the RF designs. Which is why I used those cases as examples for design choices Canon made, probably to get lenses which are as compact and as light as possible for the performance (and with optimised manufacturing cost I guess), and which as such would not be possible in the EF mount.
I doubt that Canon placed the rear elements of those lenses as close to the mount just to prevent the use of TCs
I do agree that the things like the the 100-500 extender partial incompatibility and elimination of the drop-in filter slot from the 100-300 are not due to the RF mount directly, but rather design choices made by Canon for those lenses. Worth noting that the EF 70-300L had the same characteristic as the RF 100-500, it worked with TCs but only from 250-300mm.
Didn't know about the EF 70-300L partial incompatibility, thought that the 100-500 was the first one with such a limitation
 
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I don't know whether Sony extenders impose similar minimum focal length restrictions, but the fact that they produce an excellent and affordable 200-600 makes it a moot point anyway.
Sony teleconverters also extend into the rear of the lens. They are compatible with the 70-200/2.8GM & GMii, 100-400GM, 200-600G, 400/2.8GM, and 600/4GM.

The 200-600G works well with the 1.4x TC giving an 840/9 on the long end. The 2x TC is not a great combination with and of the zooms (as is pretty much always the case) and you're probably better off cropping & upscaling if needed.
 
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