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Flange Distance m4/3
  
 
e6filmuser
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p.1 #1 · p.1 #1 · Flange Distance m4/3


When micro 4/3 was announced, so far as I remember, the register or flange distance was understood to be 20mm. Looking at various databases, the value of 19.25mm is now widely quoted and I have seen one example of 20mm.

What is the true value, or is this another variable "standard"? The issue arose elsewhere in the context of adapters for legacy lenses and their ability to focus at infinity. My adapters seem to be based on it being 20mm.

Harold




Jan 15, 2017 at 09:43 AM
mcbroomf
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p.1 #2 · p.1 #2 · Flange Distance m4/3


I've used these 2 sites in the past which report m4/3 as 19.25mm. I can't imagine how it could be variable, otherwise lenses could not be interchangeable without risking good infinity focus.

http://www.graphics.cornell.edu/~westin/misc/mounts-by-register.html
http://en.wikipedia.org/wiki/Flange_focal_distance

I looked on the official m43 website but could not find a specification page.

Mike



Jan 15, 2017 at 10:57 AM
mcbroomf
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p.1 #3 · p.1 #3 · Flange Distance m4/3


PS, adapter makers do seem to either have sloppy tolerances, or an intentional offset. Usually though they make them a tad thin to ensure infinity (at least we've seen this in the Sony and Canon adapters for 3rd party lenses) ...


Jan 15, 2017 at 11:01 AM
mcbroomf
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p.1 #4 · p.1 #4 · Flange Distance m4/3


This may be why the spec isn't on line. I don't imagine that Canon, Nikon etc publish theirs specs either so perhaps the published tables are all from physical measurements.

"Four-Thirds is not an open standard; Olympus controls access to the design specifications and no unauthorised third-party companies are able to use the Four-Thirds logo or create supported peripherals for the system."
http://camerapedia.wikia.com/wiki/Micro_Four_Thirds



Jan 15, 2017 at 11:09 AM
e6filmuser
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p.1 #5 · p.1 #5 · Flange Distance m4/3


mcbroomf wrote:
This may be why the spec isn't on line. I don't imagine that Canon, Nikon etc publish theirs specs either so perhaps the published tables are all from physical measurements.

"Four-Thirds is not an open standard; Olympus controls access to the design specifications and no unauthorised third-party companies are able to use the Four-Thirds logo or create supported peripherals for the system."
http://camerapedia.wikia.com/wiki/Micro_Four_Thirds


Mike,

Thanks. I like the idea of the spec being confidential. Anyone with a bit of nous has only to take a lens of known registration distance, e.g. an Olympus OM, at 46.0 mm. Setting the lens at infinity and maximum aperture, and then getting it (detached) to form an image on an m4/3 sensor, and seeing how that relates to the flange position, will permit measurement and deduction by subtraction. So, if the OM is 26mm from the flange the registration is 20mm.

I have done this for lenses of (to me) unknown flange distance.

Harold



Jan 15, 2017 at 01:40 PM
notherenow
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p.1 #6 · p.1 #6 · Flange Distance m4/3


Pretty sure 19.25 is right.

Sony E mount is 18mm and there are adapters to fit M4/3 lenses on E mount that are very thin.



Jan 16, 2017 at 04:22 AM
 

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AmbientMike
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p.1 #7 · p.1 #7 · Flange Distance m4/3


Found 4 websites that said 19.25, including Wikipedia. So that's probably it.

The last adapter I got seems to be made for 20mm Either that or its screwed up and they made it long Where did you see that?

0.75 mm would be a big deal, imo, especially given the shorter fl of m4/3 lenses.



Jan 17, 2017 at 01:15 AM
genji
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p.1 #8 · p.1 #8 · Flange Distance m4/3


e6filmuser wrote:
Mike,

Thanks. I like the idea of the spec being confidential. Anyone with a bit of nous has only to take a lens of known registration distance, e.g. an Olympus OM, at 46.0 mm. Setting the lens at infinity and maximum aperture, and then getting it (detached) to form an image on an m4/3 sensor, and seeing how that relates to the flange position, will permit measurement and deduction by subtraction. So, if the OM is 26mm from the flange the registration is 20mm.

I have done this for lenses of (to me) unknown flange distance.

Harold


I'm at a loss to understand what benefits are provided by keeping the flange focal distance confidential. If "anyone with a bit of nous" can figure it out, why would a manufacturer not publish the actual value?



Jan 17, 2017 at 09:46 AM
e6filmuser
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p.1 #9 · p.1 #9 · Flange Distance m4/3




I'm at a loss to understand what benefits are provided by keeping the flange focal distance confidential. If "anyone with a bit of nous" can figure it out, why would a manufacturer not publish the actual value?


Quite so. So where is it?

Harold



Jan 17, 2017 at 10:39 AM
genji
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p.1 #10 · p.1 #10 · Flange Distance m4/3


More to the point, why did you write that you "like the idea of the spec being confidential"?

e6filmuser wrote:
Quite so. So where is it?

Harold



Jan 17, 2017 at 11:17 AM
e6filmuser
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p.1 #11 · p.1 #11 · Flange Distance m4/3


genji wrote:
More to the point, why did you write that you "like the idea of the spec being confidential"?


That was ironic/sarcastic!

Harold



Jan 17, 2017 at 11:29 AM







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