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Lens to sensor distance?

Discussion in 'Open Discussion' started by voltcontrol, May 16, 2013.

  1. voltcontrol

    voltcontrol Mu-43 Regular

    133
    Apr 26, 2013
    I can't seen to find what the (back of the) lens to sensor distance is of M4/3?
    Who knows and/or has a good source on this?
     
  2. Rudy

    Rudy Mu-43 Veteran

    449
    Jan 24, 2013
    Oakland, CA
  3. speedandstyle

    speedandstyle Mu-43 Hall of Famer

    It is also called "flange distance" and more correctly "register". Here is a link showing almost all of the camera mount registration distances.

    Camera Mounts Sorted by Register

    Yes m4/3 is 19.25mm
     
  4. slothead

    slothead Mu-43 All-Pro

    Aug 14, 2012
    Frederick, MD
    All my adapted lenses seem to be farther from the sensor than my native lenses. I'm curious why you're asking.
     
  5. dwig

    dwig Mu-43 Top Veteran

    622
    Jun 26, 2010
    Key West FL
    There is no fixed "lens to sensor" distance. As others have stated, there is a "fixed" mounting flange to sensor distance known as the mount's "register".

    There is some practical maximum protrusion distance (distance from flange to rearmost protrusion) to avoid impacting any body component (e.g. sensor cover glass, ...) that sticks forward of the actual sensor's imaging plane. I've never seen this number published for m43.
     
  6. voltcontrol

    voltcontrol Mu-43 Regular

    133
    Apr 26, 2013
    I'm still tying tofigure all of this out but original system register distance X a certain crop factor should calculate the correct distance?

    Glad to reply, I need some data because I'm going to build a (simple) lens.
     
  7. Petrochemist

    Petrochemist Mu-43 Top Veteran

    652
    Mar 21, 2013
    N Essex, UK
    Mike
    Crop factor has nothing to do with it.
    The register of a lens is an intrinsic property of the lens, and part of the specification of the mount system.

    Over simplifying, if the lenses register is greater than the bodes designed register then an adapter can be made (there are rare exceptions if the lens is narrow enough, or where the mount is too wide).
     
  8. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    I just realized something when I looked at those tables with the register istances listed... how is it that we've been able to mount C-mount lenses on our m4/3 systems, even though the register is shorter on the C-mount? :/ Do they still infinity focus?
     
  9. DeeJayK

    DeeJayK Mu-43 Hall of Famer

    Feb 8, 2011
    Pacific Northwest, USA
    Keith
    Yeah, they do. The adapters are built in such a way that the C-mount lens actually recesses into the :43: mount.
     
  10. RobWatson

    RobWatson Mu-43 Hall of Famer

    Well, some do and some do not. There is a bit of room between the flange and the shutter/baffles so long as the lens in question does not touch anything it can go right up to those surfaces.

    I don't know if that space is defined in the MFT spec but it certainly is not in c-mount or pretty much most of any format I've been able to dig up. Kind of a "no-mans-land" where only the brave fear not to tread. I have several c-mount lenses that do not fit into c-mount cameras for exactly this reason!

    For example Fujinon makes a 25mm F0.85 c-mount lens that has a read element/group that protrudes a full 8mm past the flange - very few c-mount cameras have that much room. Also Kowa 8mm F1.4 lens has a protrusion when attempting to focus to infinity hits stuff in several c-mount cameras (I modified the cameras) and in my E-P1.

    On the other end the Navitar 50mm F0.95 lens body diameter is simply too wide to even fit all the way into an MFT adapter by ~3mm so no way to achieve infinity focus there (works fine for close-up work when a 5mm extension is added).
     
  11. voltcontrol

    voltcontrol Mu-43 Regular

    133
    Apr 26, 2013
    I understand what you are saying, but following your explanation the mu4/3 adapters should have length .register length of 'original' system - 19.25mm.
    Is that always the case?
     
  12. DeeJayK

    DeeJayK Mu-43 Hall of Famer

    Feb 8, 2011
    Pacific Northwest, USA
    Keith
    If they want to focus correctly that is the case.
     
  13. voltcontrol

    voltcontrol Mu-43 Regular

    133
    Apr 26, 2013
    :eek: :2thumbs:
     
  14. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    Yeah, that makes perfect sense. C-mount has a smaller radius so I can see how that would work. :)
     
  15. RobWatson

    RobWatson Mu-43 Hall of Famer

    Yeah, that's the Navitar 50mm F0.95 ... can't see the 5mm extension in that pic. I'm a softy for big glass. Sadly, pretty significant aberrations even when stopped down - unless you like that sort of thing. Fast tho ...