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Basic question about M4/3 lens geometry

Discussion in 'Native Lenses' started by tanngrisnir3, Nov 12, 2011.

  1. tanngrisnir3

    tanngrisnir3 Mu-43 Top Veteran

    594
    Oct 18, 2011
    I'm still a little new to this, and I keep hearing differing statements from all over the place about M4/3 native lenses and their 35mm equivalents.

    It's usually stated that in 35mm format terms, a M4/3 lens will be double the focal length, but I have questions about that.

    A. Does that mean if I put on a GH2 a 50mm 1.8 Canon prime with an adapter that it will actually be a 100mm 1./8 in real terms?

    B. Does this apply to native M4/3 lenses on M4/3 cameras? IOW, if I put 12mm 1.8 on a GH2, it's not going to actually render results that are 24mm, but actually be 12mm?

    Sorry, new to this type of camera, and still feeling my way around.
     
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  2. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    First - focal length is focal length, regardless if you mount it on a compact, m43, APSC, full frame, or medium format, it's always a 12 mm lens.

    When we say "equivalent" we are saying that the field of view is approximately the same. So that 12 mm lens on m43 will "see" the same width and height as a 24 mm lens mounted on a full frame /35 mm camera.

    Now, since the sensor is smaller, and you're using a shorter lens for the same field of view, the depth of field is larger - more stuff is in focus front to back in the scene, by approximately the sensor crop factor. So, your 12/1.8 will present a scene like a 24/3.6 mounted on a full frame camera.

    If you are not familiar with what the field of view for certain focal lengths look like in your mind, then none of this really matters. Just learn what a 12 mm lens field of view looks like on your camera,
     
    • Like Like x 1
  3. shnitz

    shnitz Mu-43 Top Veteran

    989
    Aug 25, 2011
    Austin, TX
    Nothing at all happens to the focal length. What happens, is because are sensors are so small compared to 35mm, that we can use half the focal length to capture the same image. It would be similar to taking a photo with a Nikon or Canon, and then only using 1/4 of the picture by cutting the rest of it away (a.k.a. cropping the image). Use google, plus a few creative search terms related to crop factor, and it will all become clear. Here are two links to get you started:
    Crop factor - Wikipedia, the free encyclopedia
    DSLR Magnification
     
  4. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    The simple answers are A) Yes, and B) Yes. There may be other technicalities involved but the way you're understanding the concept it is correct. No need to confuse the issue further...
     
  5. tanngrisnir3

    tanngrisnir3 Mu-43 Top Veteran

    594
    Oct 18, 2011
    Thanks. So (and I believe this was addressed elsewhere, as well) do I understand that aperture, however, remains constant? As in, there is no multiplying factor when comparing M4/3 apertures to 35mm?
     
  6. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    In regards to lens speed, Yes. :)
     
  7. shnitz

    shnitz Mu-43 Top Veteran

    989
    Aug 25, 2011
    Austin, TX
    In regards to exposure, as Ned says, then yes aperture is irregardless of camera format. However, compared to 35mm film, the depth of field is rendered differently. It's effectively 2 stops more, so if you are using a 50mm lens at f/2.8 on our cameras, your "effective" depth of field is the same as a 100mm f/5.6. Feel free to play with this calculator to get an idea:
    Online Depth of Field Calculator

    This isn't bad or good, just something to be aware of. If I'm taking a picture of a group of friends, for example, or a cool car, I can take a picture at f/1.8 or f/2 and still have enough depth of field, so I don't have to use flash nearly as soon.
     
    • Like Like x 1
  8. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    ...and if you're shooting action, then fast lens speed with large DOF is absolutely wonderful!
     
  9. tanngrisnir3

    tanngrisnir3 Mu-43 Top Veteran

    594
    Oct 18, 2011
    Thanks, Ned & schnitz, those are exactly the answers I was looking for.

    When reading lens reviews, I seem to continually come across criticism of the M4/3 lenses (esp the Panny 7-14) because they double the aperture value in terms of exposure. That made zero sense to me.

    Turns out, they don't after all.

    Problem solved.
     
  10. meyerweb

    meyerweb Mu-43 Hall of Famer

    Sep 5, 2011
    Yes, as you've realized, you're not the only one confused by this. But at least you understood you were confused. There are a lot of people who are totally wrong on this topic but refuse to be corrected.
     
  11. ph.

    ph. Mu-43 Rookie

    24
    Feb 14, 2010
    norway
    Not what you had in mind when asking, but there is another important geometrical property: VOLUME.

    Since Native MFT lenses, as opposed to fullframe or APS-C, are designed to cover a smaller sensor, they do not need large radius bits of glass+ metal or plastic, so they can be made to take up less space & to weigh less even at the same speed and focal length.

    p.