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Barrel Markings?

Discussion in 'Adapted Lenses' started by Cruzan80, Aug 24, 2012.

  1. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    Question for the group:

    I understand that the effective focal length when using these lenses from 35mm to m4/3 is approx. 2x. When using the focus range numbers printed on the barrel, are these also doubled, or not since the lens is still focusing at the same distance away, and the sensor is just "cropped"? How about the DoF sizings (16, 8, 4, R, 4, 8, 16) that let me know how much leeway to either side I have? I understand the aperture doesn't change (measurement is based on size of lens vs opening created), but I have heard different answers on if the DoF changes for a given lens at the same aperture opening, depending on the sensor size (35mm vs m4/3).

    Of course, all of these questions assume the lens barrel markings are accurate at their given distances when put on a 35mm body. Sorry if they have been asked before, couldn't see anything directly stating the above.
  2. nseika

    nseika Mu-43 Veteran

    Nov 22, 2010
    Jakarta, Indonesia
    All the lens properties are for the lenses :) 
    The lens is projecting the same image to the same distance regardless of sensor size

    So the distance scale and DoF should be the same
    But if you're using cheap adapter, give some tolerance because it can be a tiny bit too long or too short than needed.
  3. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    Yes, the DoF scale also changes by a factor of two or one stop. So, for example, you would use the f/8 scale markings when the aperture is set to f/11.

    DoF is not a property of the lens, but a subjective property of the human visual system. DoF is defined by the permissible circle of confusion which in turn is defined by format size.
    • Like Like x 1
  4. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    So if the DoF scale has 4, 8, 11, 16, go one smaller than the aperture calls for? But the distance focusing would be the same.

    I thought the focus part was correct as the "cropping" vs "effective" focal distance (that I have finally wrapped my mind around what parts affect me, vs what parts affect the lens).

    Wasn't sure exactly how DoF was calculated in general, so wasn't sure of the mechanics of changing "effective" focal length.
  5. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    Right, the DoF markings are off by one stop and you use the marking one stop open from the set aperture. Which means you have no DoF scale markings for the maximum aperture.

    The distance scale is not affected.

    The focal length does not change.

    The aperture does not change in relation to exposure.

    The angle of view changes because of the format--this is really what "crop factor" is all about as angle of view is a product of both focal length AND format size. And format is the variable that changes in this case.
  6. Ig7

    Ig7 Mu-43 Veteran Subscribing Member

    Aug 24, 2011
    What about focusing distance for OIS on an OMD? Would you set it to 25 or a 50 if you are using a 50 adaptive lens?
  7. meyerweb

    meyerweb Mu-43 Hall of Famer Subscribing Member

    Sep 5, 2011
    Focal length is focal length. A 25mm lens is still a 25mm lens, and a 50mm lens is still a 50mm lens, regardless of whether it was designed for m43, FF, or even medium format. The camera doesn't know what format the lens was designed for. So set IBIS (not OIS, which exists only in native lenses), to the actual focal length of the lens. A 50mm legacy lens will act pretty much the same (in terms of magnification and camera shake) as one of the 45mm native lenses.
  8. Ig7

    Ig7 Mu-43 Veteran Subscribing Member

    Aug 24, 2011
    Thank you
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