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

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))

Which in layman’s terms, is a calculation that takes into account the flange distance of a mount. the size of the mount itself against the size of the image sensor.

In Fujifilm’s mind, this formula tells us and them how difficult it is to design top performing lenses for a particular mount. The winner? The EF-M mount from Canon. The latest RF mount from Canon didn’t do as well according to the formula.

Company Mount Value Angle Format Flange Distance Diameter Sensor Diagonal
Canon EF-M 58.6 APS-C 18 47 26.8
Leica L (TL) 54.5 APS-C 20 48.8 28.2
Sony E (NEX, E-mount) 52.9 APS-C 18 46.1 28.2
Fujifilm X 48.1 APS-C 17.7 44 28.2
m43’s (Olympus, Panasonic,etc) MFT 46.0 Micro 43’s 19.3 38 21.6
Nikon Z 40.2 Full Frame 16 55 43.3
Canon RF 30.0 Full Frame 20 54 43.3
Fujifilm G 21.6 44×33 26.7 65 54.8
Hasselblad XCD 17.6 44×33 20 61 54.8
L-mount Alliance L 15.7 Full Frame 20 48.8 43.3
Sony E (FE) 8.9 Full Frame 18 46.1 43.3

As you can see in the table above, the EF-M mount takes the top prize, while the RF mount comes in second for flexibility behind Nikon’s Z mount and well ahead of Sony’s E(FE) mount.

Canon News shows us what the EF-M mount would look like using this formula for the EF-M mount with a full frame image sensor.

Company Mount Value Angle Format Flange Distance Diameter Sensor Diagonal
Canon EF-M 58.6 APS-C 18 47 26.8
Canon EF-M 11.7 Full Frame 18 47 43.3

I think this likely shows us that the EF-M mount was never intended to be full frame and makes the introduction of the RF mount much needed for the full frame mirrorless application.

You can check out the full article about the value angle over at Profifoto (Google Translated Link).

Nothing here means you can’t make amazing lenses for any of these mounts, Fujifilm merely uses this formula to discuss how “easy” it is to get stellar optical performance from new lens designs. Canon’s RF mount is going to lead to some unique and one-of-a-kind designs, which may be more difficult on the E (FE) mount for Sony.

addola

Sold my soul for a flippy screen
Nov 16, 2015
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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.
 

dcm

Good or bad - it's not the gear.
Apr 18, 2013
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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 diagonal
samsung nx mini
115.7​
1"
7.0​
38.0​
15.9​
Nikon 1
70.7​
1"
17.0​
40.0​
15.9​
Leica L
60.7​
aps-c
20.0​
51.6​
28.2​
Canon EF-M
58.6​
APS-C
18.0​
47.0​
26.8​
Leica L (TL)
54.5​
APS-C
20.0​
48.8​
28.2​
Sony E (NEX, E-mount)
52.9​
APS-C
18.0​
46.1​
28.2​
Fujifilm X
48.1​
APS-C
17.7​
44.0​
28.2​
m43’s (Olympus, Panasonic,etc) MFT
46.0​
Micro 43’s
19.3​
38.0​
21.6​
Nikon Z
40.2​
35
16.0​
55.0​
43.3​
canon EF-S
34.4​
aps-c
44.0​
54.0​
26.8​
Canon RF
30.0​
35
20.0​
54.0​
43.3​
Leica L
23.4​
35
20.0​
51.6​
43.3​
Fujifilm G
21.6​
44×33
26.7​
65.0​
54.8​
pentax k
19.7​
aps-c
45.5​
44.0​
28.2​
nikon dx
19.3​
aps-c
46.5​
44.0​
28.2​
Hasselblad XCD
17.6​
44×33
20.0​
61.0​
54.8​
L-mount Alliance L
15.7​
35
20.0​
48.8​
43.3​
Canon EF
13.9​
35
44.0​
54.0​
43.3​
Sony E (FE)
8.9​
35
18.0​
46.1​
43.3​
Rolleiflex SL35
8.2​
35
44.6​
49.7​
43.3​
Leica R
6.9​
35
47.0​
49.0​
43.3​
Canon FD/FL
6.4​
35
42.0​
48.0​
43.3​
Leica M
1.4​
35
27.8​
44.0​
43.3​
pentax k
0.9​
35
45.5​
44.0​
43.3​
Nikon F/…
0.9​
35
46.5​
44.0​
43.3​
Rolleiflex SL66
-8.8​
6x6
102.8​
69.0​
84.9​
mamiya 645
-11.7​
6x4.5
63.3​
62.0​
75.0​
Hasselblad
-12.1​
6x6
74.9​
69.0​
84.9​
pentax 6x7
-13.6​
6x7
85.0​
72.0​
92.2​
mamiya rb67
-16.4​
6x7
112.0​
60.0​
92.2​
mamiya rz67
-17.4​
6x7
105.0​
60.0​
92.2​
 
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Maximilian

The dark side - I've been there
Nov 7, 2013
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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 :unsure:
 

dcm

Good or bad - it's not the gear.
Apr 18, 2013
742
79
@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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SwissFrank

EOS RP
Dec 9, 2018
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This is about 3 kinds of BS, sorry! :-D

1) (mistake, I misread the initial post)

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.

3) and to answer my own question: on a mirrorless the REAL question isn't what the flange distance is, but how close the lens can get. There may be additional limitations in the AE or AF systems (for instance the old Leica M5 had an AE sensor on a semaphore that would impact a couple of the wide-angle lenses). But if not, you can crawl all the way in there. The Contax G2 16mm Hologon is an example, as well as their 28mm and 21mm. Canon and Nikon both made 21mm lenses for the SLRs, if I recall correctly, that required the mirror to be locked up before use (and thus came with an auxiliary viewfinder). (I think 21mm's attraction is that it's 90 degrees and thus able to take in an entire room from the corner, useful for architecture.)
 
Last edited:

mb66energy

EOS 6D MK II
Dec 18, 2011
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www.MichaelBockhorst.de
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.
 
Jun 16, 2019
3
1
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.

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.

3) and to answer my own question: on a mirrorless the REAL question isn't what the flange distance is, but how close the lens can get. There may be additional limitations in the AE or AF systems (for instance the old Leica M5 had an AE sensor on a semaphore that would impact a couple of the wide-angle lenses). But if not, you can crawl all the way in there. The Contax G2 16mm Hologon is an example, as well as their 28mm and 21mm. Canon and Nikon both made 21mm lenses for the SLRs, if I recall correctly, that required the mirror to be locked up before use (and thus came with an auxiliary viewfinder). (I think 21mm's attraction is that it's 90 degrees and thus able to take in an entire room from the corner, useful for architecture.)
In the formula it's 2arctan(xxxx/2yyy) so the 2 cannot bei canceled out. Nonetheless I agree to question the validity of the formula.
 
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BillB

EOS 6D MK II
May 11, 2017
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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.

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.

3) and to answer my own question: on a mirrorless the REAL question isn't what the flange distance is, but how close the lens can get. There may be additional limitations in the AE or AF systems (for instance the old Leica M5 had an AE sensor on a semaphore that would impact a couple of the wide-angle lenses). But if not, you can crawl all the way in there. The Contax G2 16mm Hologon is an example, as well as their 28mm and 21mm. Canon and Nikon both made 21mm lenses for the SLRs, if I recall correctly, that required the mirror to be locked up before use (and thus came with an auxiliary viewfinder). (I think 21mm's attraction is that it's 90 degrees and thus able to take in an entire room from the corner, useful for architecture.)
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.
 

Kit.

EOS 6D MK II
Apr 25, 2011
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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

EOS 7D MK II
Mar 25, 2012
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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.
 

BillB

EOS 6D MK II
May 11, 2017
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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.
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

EOS RP
Jan 21, 2015
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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.