Patent: Canon RF-S 15-70mm f/4 and RF-S 15-85mm f/2.8-4

Jul 21, 2010
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But it doesn't really change my question regarding the wide-end lens-correction needed in post, and how to interpret F- and T-stops in the wide end for such designs...
There is no optical relationship between the aperture and the type of optical corrections needed/forced for the wide end of MILC zoom lenses. There is, in some cases, a difference in apparent focal length whereby Canon is patenting the focal range of the lens incorporating digital corrections rather then the 'true' focal length which has mechanical vignetting at the wide end in addition to ample distortion. That's actually why the image height at the wide end is not sufficient to cover a FF sensor, and led to CRguy and others erroneously suggesting RF (full frame) lens patents were intended for APS-C sensors.

F-stop and T-stop have never been directly correlated, although obviously T-stop will be slower than f-stop. Convention is that cine lenses are specified for T-stop and still lenses are specified for f-stop. The measured T-stops of mirrorless lenses are in a similar range to those for DSLR lenses, and as before the consumer grade lenses tend to have a slower T-stop relative to f-stop than the L-series lenses.
 
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AJ

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I’ll point out (again) that the patent for the RF 100-500 was f/4-6.3 while the lens is f/4.5-7.1, and the patent for the RF 100-400 was f/5-7.1 while the lens is f/5.6-8. Seems likely the 15-85, if ever made, will be f/3.5-6.3.
... which makes me wonder if some lenses are optically capable of letting in more light, but the diaphragm has been limited by the manufacturer to only allow fstops that yield outstanding performance, to please the pipel-peepers.
Because I doubt an f/3 lens would get rounded up to f/3.5 rather than rounded down to f/2.8
 
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Dragon

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I wonder if the "faster" wide-end (f2.8 vs f3.5 in old lens) is related to the optically lens-correction required at the wide end of the new RF-S lens-design?
I mean is it really faster as also being a faster T-stop (taking more light in)?
Any optical specialists having an understanding of this?
Or simply thanks to a shorter flange distance. Short back focus distances makes wide and fast easier. I think the reduced geometric correction in many newer lenses has more to to with keeping the size and weight down than anything else. Adding correction elements adds bulk and lowers acuity. Digital correction adds no bulk and often offers superior acuity. The RF 16mm f/2.8 is a pretty good example. Try and find a 16mm lens that fast anywhere near the same size and weight that offers equal or better IQ. My bet is that the RF-s 15-85 will be substantially smaller and lighter than the EF-s version, which is pretty chunky.
 
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Stig Nygaard

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Or simply thanks to a shorter flange distance. Short back focus distances makes wide and fast easier. I think the reduced geometric correction in many newer lenses has more to to with keeping the size and weight down than anything else. Adding correction elements adds bulk and lowers acuity. Digital correction adds no bulk and often offers superior acuity. The RF 16mm f/2.8 is a pretty good example. Try and find a 16mm lens that fast anywhere near the same size and weight that offers equal or better IQ. My bet is that the RF-s 15-85 will be substantially smaller and lighter than the EF-s version, which is pretty chunky.

Yes, of course the lens-designs are about "keeping the size and weight down than anything else". My question was more about possible sideeffects of that...

My point is that light ain't collected from the full sensor in the wide end with those lens designs. For example lets imagine that 80% of the sensor is used for the final photo at the widest position of the lens, but at longer focal lengths light is collected from the full sensor surface.

Or lets say you are shooting manual at 35mm at f/4 and 1/250s with such a zoom-lens. You then zoom to it widest 15mm, change aperture to f/2.8 and shutter to 1/500s. Would that give similar exposure, or does it actually not collect as much light this way?
Similar (but optically not for same reason) to a macro-lens typically let 1-2 "stops" less light in at it shortest focus-distances, than it does at normal focus distances using same aperture.

(PS. I don't know if neuroanatomist understood my point and if he gave me the answer - I honestly only understood half of what he wrote)
 
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Yes, of course the lens-designs are about "keeping the size and weight down than anything else". My question was more about possible sideeffects of that...

My point is that light ain't collected from the full sensor in the wide end with those lens designs. For example lets imagine that 80% of the sensor is used for the final photo at the widest position of the lens, but at longer focal lengths light is collected from the full sensor surface.
The mechanical vignetting is not that bad. More like 1-3% of the frame is black before correction.

Or let’s say you are shooting manual at 35mm at f/4 and 1/250s with such a zoom-lens. You then zoom to it widest 15mm, change aperture to f/2.8 and shutter to 1/500s. Would that give similar exposure, or does it actually not collect as much light this way?
I’m sure it would, and most likely that would not require ‘fudging’ the exposure. That’s not always the case, but the reason isn’t distortion it’s light at extreme oblique angles being lost. That occurs with f/1.4 and f/1.2 lenses, and the camera actually uses a higher ISO than it reports in the EXIF. I’m not sure if that occurs with RF lenses, but I know it does with EF lenses on DSLRs.

Similar (but optically not for same reason) to a macro-lens typically let 1-2 "stops" less light in at it shortest focus-distances, than it does at normal focus distances using same aperture.
Yes, the ‘effective aperture’ at macro magnification is different.

(PS. I don't know if neuroanatomist understood my point and if he gave me the answer - I honestly only understood half of what he wrote)
Apologies! If you were suggesting the patent starts at f/2.8 but if it’s an f/3.5 lens it’s because Canon will electronically close the aperture a bit, then no.

What I’m saying is the focal lengths in the patent take optical correction of distortion into account. The patented 15-85 will likely be ~14mm at the wide end. The RF 14-35 is actually a little wider than 13mm uncorrected. But none of that will affect aperture, and it’s not enough to affect f/number (e.g., a 15/2.8 needs an aperture of 42mm, if it’s really 14mm then it would be f/3, which Canon would still call f/2.8.

But as I said, I’d bet good money an RF-S 15-85 will start at f/3.5.
 
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Dragon

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But as I said, I’d bet good money an RF-S 15-85 will start at f/3.5.
Likely true but if it does start at f/2.8, it will be f/3.5 by 17mm. One of the side effects of under-illumination is that the area that is illuminated will have more concentrated light (exactlly the opposite of the macro lens case), and the exposure needs to be set for the area that will be used in the final image, so you can see where f/2.8 at the widest setting might happen. My bet is that the lens will be considerably smaller and lighter than the EF-s 15-85 which is the third heaviest of all EF-s lenses (after the 17-55 and 18-200).
 
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Ozarker

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"Content Creator" seems to be a term for someone who uploads contend to a social media platform.
Yes. "Content Creators" on YouTube have really helped me with car repairs, photography and all kinds of other things. There are some great channels out there that serve up information in a very down to earth way and sometimes humorous manner. Then there's that obscure guy who tells you what size resistor to use when bypassing various sensors on an ancient old farm truck.

BTW: Micheal, creator of "Hook, Line, and Chill" uses a drone, GoPro, and Canon camera w/ L lenses.Lots of YouTubers do. Each buys what they want.
 
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BTW: Micheal, creator of "Hook, Line, and Chill" uses a drone, GoPro, and Canon camera w/ L lenses.Lots of YouTubers do. Each buys what they want.
There seems to be some myth that everyone on YouTube uses Sony.
A lot of normal everyday people tend to use Canon.
Sony gave away a lot of gear to influencers.
Camera sections are starting to disappear in department stores and electronics stores which were where normal everyday people bought cameras.
Canon had the strongest brand and the cheapest cameras.
They plan on maintaining their market share.
The R50 is one heck of a Camera but I am curious about how they plan to get those in the hands of people.
 
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I'd guess that the majority of "content creators" are novices trying their hand at vlogging (oops, I mean *creating*), and unlikely to want to spend much until they've gained experience. So yes, Canon will give them the cheapest option, and they'll be unlikely, as novices, to recognise the better quality that a more expensive lens would provide. Also of course, Canon want to be price-competitive with Sony.
The R50 is a big improvement over the M50 but the R50 kit lens starts at 18 mm while the M50 kit lens starts at 15 mm.
The M50 is ready for vlogging out of the box.
Plus there is an additional 11-20 mm UWA lens available as well.
 
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photofrankdzi

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There will obviously be more RF-S lenses coming coming this year as well as next year. Today we see a patent for a couple of RF-S optical formulas. One of these optical formulas will likely be close to a future product by the looks of the designs. Canon RF-S 15-70mm f/4 Canon RF-S 15-70mm f/2.8-4

See full article..

There will obviously be more RF-S lenses coming coming this year as well as next year. Today we see a patent for a couple of RF-S optical formulas. One of these optical formulas will likely be close to a future product by the looks of the designs. Canon RF-S 15-70mm f/4 Canon RF-S 15-70mm f/2.8-4

See full article...
If the Lenses
Canon RF-S 15-70mm f/4 or Canon RF-S 15-70mm f/2.8-4
would be "L" - category - it would be "The DREAM - Couple" with my fantastic EOS R7. (They would give the Range 24-112 compared to full-frame). At the moment I use my EOS R7 with EF-S 17-55 f:2,8 but this is more heavy and big because of the needed adaptor. Or with RF 14-35 f4 "L" which is too short at the 35 End but feels like a Dream-Combination" in the hands.
 
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Sep 20, 2020
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If the Lenses

would be "L" - category - it would be "The DREAM - Couple" with my fantastic EOS R7. (They would give the Range 24-112 compared to full-frame). At the moment I use my EOS R7 with EF-S 17-55 f:2,8 but this is more heavy and big because of the needed adaptor. Or with RF 14-35 f4 "L" which is too short at the 35 End but feels like a Dream-Combination" in the hands.
The EF-S 17-55 f/2.8 IS was not an L lens.
I won't get my hopes up so high but it would be nice.
 
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