# Fujifilm thinks the Canon EF-M mount is the best in the business for ease of lens design



## Canon Rumors Guy (Jun 15, 2019)

> Here’s an interesting one that came out of the recent X system summit by Fujifilm.
> They came up with something that is called the “value angle” when talking about the various lens mounts out there for photography.
> What is the value angle?
> The formula for value angle = 2 × arctan ((mount diameter – sensor diagonal) / (2 × flange distance))
> ...



Continue reading...


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## Dragon (Jun 15, 2019)

This may at least partially explain why the M lenses are so sharp for their size and weight.


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## addola (Jun 15, 2019)

Maybe more difficult with Sony E mount, but easier on Nikon Z mount. Nikon really needed a radically different mount because their F mount was very small.


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## ColinJR (Jun 16, 2019)

What I see here is that a full-frame canon using the EF-M mount would _still_ outperform Sony...


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## dcm (Jun 16, 2019)

Here's a few more for comparison. I'm not sure how valuable the metric is across formats since it is clearly easier to design a lens for 1" sensors and harder for medium format sensors. Kind of expected IMHO - a correlation analysis shows value angle, flange distance, and mount diameter are highly correlated to the sensor diagonal. I do like the negative value angles - not sure how to interpret that.. 


mountvalue angleformatflange distancemount diametersensor diagonalsamsung nx mini115.7​1"7.0​38.0​15.9​Nikon 170.7​1"17.0​40.0​15.9​Leica L60.7​aps-c20.0​51.6​28.2​Canon EF-M58.6​APS-C18.0​47.0​26.8​Leica L (TL)54.5​APS-C20.0​48.8​28.2​Sony E (NEX, E-mount)52.9​APS-C18.0​46.1​28.2​Fujifilm X48.1​APS-C17.7​44.0​28.2​m43’s (Olympus, Panasonic,etc) MFT46.0​Micro 43’s19.3​38.0​21.6​Nikon Z40.2​3516.0​55.0​43.3​canon EF-S34.4​aps-c44.0​54.0​26.8​Canon RF30.0​3520.0​54.0​43.3​Leica L23.4​3520.0​51.6​43.3​Fujifilm G21.6​44×3326.7​65.0​54.8​pentax k19.7​aps-c45.5​44.0​28.2​nikon dx19.3​aps-c46.5​44.0​28.2​Hasselblad XCD17.6​44×3320.0​61.0​54.8​L-mount Alliance L15.7​3520.0​48.8​43.3​Canon EF 13.9​3544.0​54.0​43.3​Sony E (FE)8.9​3518.0​46.1​43.3​Rolleiflex SL358.2​3544.6​49.7​43.3​Leica R6.9​3547.0​49.0​43.3​Canon FD/FL6.4​3542.0​48.0​43.3​Leica M1.4​3527.8​44.0​43.3​pentax k0.9​3545.5​44.0​43.3​Nikon F/…0.9​3546.5​44.0​43.3​Rolleiflex SL66-8.8​6x6102.8​69.0​84.9​mamiya 645-11.7​6x4.563.3​62.0​75.0​Hasselblad-12.1​6x674.9​69.0​84.9​pentax 6x7-13.6​6x785.0​72.0​92.2​mamiya rb67-16.4​6x7112.0​60.0​92.2​mamiya rz67-17.4​6x7105.0​60.0​92.2​


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## Maximilian (Jun 16, 2019)

Thanks for the longer list, dcm.

Somehow this shows to me that the sensor size is a too much important factor in this formula 
==> the smaller, the easier a high VA achieved 
I don‘t know in this „science“ is really working


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## Dragon (Jun 16, 2019)

@dcm. Note that EFs may be better than the calculation indicates because the design allows for the rear lens element to be inside the flange opening so the flange distance is effectively shorter.


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## dcm (Jun 16, 2019)

Dragon said:


> @dcm. Note that EFs may be better than the calculation indicates because the design allows for the rear lens element to be inside the flange opening so the flange distance is effectively shorter.



I realize that, but it wasn’t part of the formula.


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## mb66energy (Jun 16, 2019)

The results of this metric seem very strange: Impossible to make some technically acceptable photos with Hasselblad or Pentax RB cameras. Maybe it's the result of humans dream of one number (e.g. 42) or GUTs in phyics (grand unified theories) which describe the whole world in one sentence.

I think it's correct for quality on a fixed sensor size but never for overall image quality because a larger sensor needs less lines per mm to shine in IQ if the result is printed in the same size.


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## Tmjc.wolf (Jun 16, 2019)

SwissFrank said:


> This is about 3 kinds of BS, sorry! :-D
> 
> 1) there is a multiplier of 2 on both halves of the fraction. That could cancel out, but they didn't do so, indicating they're trying to make this look more arcane than it really is.
> 
> ...


In the formula it's 2_arctan(xxxx/2_yyy) so the 2 cannot bei canceled out. Nonetheless I agree to question the validity of the formula.


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## BillB (Jun 16, 2019)

ColinJR said:


> What I see here is that a full-frame canon using the EF-M mount would _still_ outperform Sony...


Easier lens design isn't the same thing as outperform


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## BillB (Jun 16, 2019)

SwissFrank said:


> This is about 3 kinds of BS, sorry! :-D
> 
> 1) there is a multiplier of 2 on both halves of the fraction. That could cancel out, but they didn't do so, indicating they're trying to make this look more arcane than it really is.
> 
> ...


Taken together, the diameter of the lens mount opening and the flange distance may be a constraint that increases the difficulty of designing a lens to cover a given image circle, even if the lens can protrude into the camera past th flange. 

Leaving room for IBIS and perhaps other considerations may have had something to do with the 20mm flange length decision . 4-6mm doesn't seem like a lot of room to work with to design a locking, solid and easily usable adapter with electrical contacts.


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## Kit. (Jun 16, 2019)

The formula is a measure of how fast (how bright) an image-space telecentric lens can be made for the mount without vignetting. That's all.

The formula gives a negative value if an image-space telecentric lens without vignetting is impossible for the given mount.


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## Bob Howland (Jun 16, 2019)

dcm said:


> Here's a few more for comparison. I'm not sure how valuable the metric is across formats since it is clearly easier to design a lens for 1" sensors and harder for medium format sensors. Kind of expected IMHO - a correlation analysis shows value angle, flange distance, and mount diameter are highly correlated to the sensor diagonal. I do like the negative value angles - not sure how to interpret that..


First, you have three lines for Leica L, with different mount diameters. I am assuming that the 48.8mm came from Fuji while the 51.6mm came from Wikipedia.

Second, three or four decades ago, I played with both Mamiya 645 and RB67 cameras. As I recall the RB67 mount was larger than the 645 mount.

Third, the negative angle values simply mean that the sensor diagonal is larger than the mount diameter.


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## M. D. Vaden of Oregon (Jun 16, 2019)

BillB said:


> Easier lens design isn't the same thing as outperform



In the end, your conclusion can sweep the whole matter away in the blink of an eye. Many photographers don't care what's easier to design or not. But what can it do in the end.


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## ColinJR (Jun 16, 2019)

BillB said:


> Easier lens design isn't the same thing as outperform



I’m being facetious... I do find it kind of funny that the EF-M mount is larger than Sony’s full frame e-mount—but yes, that’s not to say their lenses are less good, or easier/harder to design.


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## BillB (Jun 16, 2019)

ColinJR said:


> I’m being facetious... I do find it kind of funny that the EF-M mount is larger than Sony’s full frame e-mount—but yes, that’s not to say their lenses are less good, or easier/harder to design.





ColinJR said:


> I’m being facetious... I do find it kind of funny that the EF-M mount is larger than Sony’s full frame e-mount—but yes, that’s not to say their lenses are less good, or easier/harder to design.


The story as I understand it is that the Sony e-mount was designed for aps-c cameras as that after the fact, Sony decided to use it for their fullframe mirrorless.


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## Adelino (Jun 16, 2019)

SwissFrank said:


> This is about 3 kinds of BS, sorry! :-D
> 2) really what it amounts to is, shorter the flange distance the better. Why in hades did Canon choose 20mm, not 16mm or even 14mm, for the EF? 14-15mm would have allowed an EF-M-to-RF adapter, giving the RF another half-dozen small lenses to use, at the price of reduced sensor area, but still great for backpackability.


Canon stated they chose the 20mm to create a very robust mount, especially for larger lenses the mount needs to be very strong. That was their explanation.


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## Dragon (Jun 16, 2019)

mb66energy said:


> The results of this metric seem very strange: Impossible to make some technically acceptable photos with Hasselblad or Pentax RB cameras. Maybe it's the result of humans dream of one number (e.g. 42) or GUTs in phyics (grand unified theories) which describe the whole world in one sentence.
> 
> I think it's correct for quality on a fixed sensor size but never for overall image quality because a larger sensor needs less lines per mm to shine in IQ if the result is printed in the same size.


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## Dragon (Jun 16, 2019)

@mb66energy. Nobody said anything about "impossible", just that short and wide makes for easier lens design. There have been some fine lenses made for video cameras with dichroic prisms (very long back throw), but they typically use relay optics and require at least one more lens group. The flip side of short and wide is that it encourages the design of lenses with extreme light exit angles and that light isn't easy to receive on the sensor. This can result in a different kind of vignetting (caused by the sensor). At the end of the day there is no free lunch.


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## photonius (Jun 16, 2019)

mb66energy said:


> The results of this metric seem very strange: Impossible to make some technically acceptable photos with Hasselblad or Pentax RB cameras. Maybe it's the result of humans dream of one number (e.g. 42) or GUTs in phyics (grand unified theories) which describe the whole world in one sentence.
> 
> I think it's correct for quality on a fixed sensor size but never for overall image quality because a larger sensor needs less lines per mm to shine in IQ if the result is printed in the same size.




I think the point is about "ease of design". Because the mount diameter of the large formats is smaller than the sensor, and the long flange, it would be more troublesome to design fast lenses. The F-stops of Hasselblad lenses are similar to consumer EF-S lenses... ;-)


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## CJudge (Jun 17, 2019)

Interesting that the Fuji engineers would even bother putting this together, as how "easy" a system is to design a high-performing lens for is reliant on so many factors beyond just physics, enough to make the whole point moot, really.

Namely, the experience and specialisation of your engineering team. If the team is used to designing lenses for a specific mount diameter or flange distance or sensor size, it will likely be "easier" for them to continue to do so than it might be for a team coming from working on a different set of specs.


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## Bob Howland (Jun 17, 2019)

FWIW, I just measured the diameter of the last element on my first generation 24-70 f/2.8 L, 135 f/2 L and first generation 24 f/1.4 L lenses: 37-38mm for all three lenses. Given the position of the lens' electrical contacts to the body, I don't see how that element can be much if any larger on any EF or RF lens. Which means that none of those lenses can be telecentric on a FF sensor.

I would appreciate if you folks would make comparable measurements for M and RF mount lenses and post them here.

Thanks


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## millan (Jun 17, 2019)

I wonder why the formula doesn't calculate with the value of sensor shift. It could have an influence on value of value angle. Or am I wrong?


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## blackcoffee17 (Jun 17, 2019)

This is nice and everything but does really matter if Canon releases 1 lens every two years and one entry level plastic camera per year.


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## BillB (Jun 17, 2019)

blackcoffee17 said:


> This is nice and everything but does really matter if Canon releases 1 lens every two years and one entry level plastic camera per year.


Well, whether it matters may depend on whether you are interested in the number of new camera and lens models available or the number of cameras and lenses sold. Canon seems to be in the business of selling cameras and lenses. Lenses that are easier to design may be less expensive to manufacture and therefore easier to sell.


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## YuengLinger (Jun 17, 2019)

Friendly praise from a competitor. Now, is there a merger in the works?


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## magarity (Jun 17, 2019)

M. D. Vaden of Oregon said:


> In the end, your conclusion can sweep the whole matter away in the blink of an eye. Many photographers don't care what's easier to design or not. But what can it do in the end.


Do they not care when easier design = less costly? That isn't always the case but probably is in most.


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## melgross (Jun 17, 2019)

dcm said:


> I realize that, but it wasn’t part of the formula.



I’ve been saying that too. The actual flange distance and diameter is only part of the question. While I might be wrong in this, it looks as though the RF mount of Canon also allows the lens to protrude into the mount.

What this means is that when you remove a lens, and the rear has to rotate with the body, a mount that has a rectangular opening inside won’t allow that internal rotation. That means that if a rectangular element does protrude, the camera/body will need to rapidly withdraw that element before the lens is rotated. How that can be done without the user doing something, or without turning the camera off, forcing the lens to withdraw the element, I don’t know.


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## melgross (Jun 17, 2019)

What’s interesting in Fuji’s listing is that their own L mount doesn’t fare very well. If they really consider this factor to be important enough to have had a talk regarding it, along with the subsequent chart, then why did they become part of this alliance in the first place?

Personally, I don’t believe it’s terribly important. It only becomes important when considering lens price and size. And that’s only true when the differences are very significant.


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## miggyt (Jun 18, 2019)

the tried and test canon EF mount has a 54mm diameter and is much larger than nikon's F mount and sony's E mount. correct me if I'm wrong, but canon's current EF mount is already more than capable even with the long flange distance. maybe canon should just continue using the current EF mount and convert all their DLSRs into mirrorless by replacing OVF with EVF and replacing the flapping mirror with maybe a built-in ND filter that I'm sure a lot of people will love? doesn't canon's dual pixel tech already work so well? sounds like a win-win situation for me. people need not replace their EF lens collection, and get to continue using the well-loved canon DSLR ergonomics. or am I missing something?


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## Adelino (Jun 18, 2019)

miggyt said:


> the tried and test canon EF mount has a 54mm diameter and is much larger than nikon's F mount and sony's E mount. correct me if I'm wrong, but canon's current EF mount is already more than capable even with the long flange distance. maybe canon should just continue using the current EF mount and convert all their DLSRs into mirrorless by replacing OVF with EVF and replacing the flapping mirror with maybe a built-in ND filter that I'm sure a lot of people will love? doesn't canon's dual pixel tech already work so well? sounds like a win-win situation for me. people need not replace their EF lens collection, and get to continue using the well-loved canon DSLR ergonomics. or am I missing something?


I think your comment is about ten months late...


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## PerKr (Jun 18, 2019)

melgross said:


> What’s interesting in Fuji’s listing is that their own L mount doesn’t fare very well. If they really consider this factor to be important enough to have had a talk regarding it, along with the subsequent chart, then why did they become part of this alliance in the first place?
> 
> Personally, I don’t believe it’s terribly important. It only becomes important when considering lens price and size. And that’s only true when the differences are very significant.



that's Panasonic though. Along with Sigma and Leica.


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## Dragon (Jun 18, 2019)

millan said:


> I wonder why the formula doesn't calculate with the value of sensor shift. It could have an influence on value of value angle. Or am I wrong?


Sensor shift just means the lens illumination area has to be bigger than the sensor by the peak to peaks amount of the sensor movement, so yes, it does have an effect (that is, unless the manufacturer accepts additional vignetting due to sensor shift, and I think most do).


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## miggyt (Jun 19, 2019)

Adelino said:


> I think your comment is about ten months late...


sadly yes


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## Pancho (Jun 20, 2019)

This Value Angle is simply that:


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