Micro 4/3rds

Discussion in 'Digital Photography' started by G.T., May 28, 2010.

  1. G.T. macrumors 6502a

    Joined:
    Jul 12, 2008
    #1
    I just need this cleared up.

    So many people say it different I'm not sure who's right. With micro 4/3rds they say double focal length so my f1.7 20mm is (40mm equivalent to 35mm) but some people will say its f3.4 40mm. Should you double aperture value? does that mean my great 20mm lens at f1.7 is only really letting the same light and bokeh as a 40mm lens at f3.4 (I mention bokeh as someone was surprised I shot at f1.7 and the background looked more like f3-4 to them)?
     
  2. jackerin macrumors 6502a

    Joined:
    Jun 29, 2008
    Location:
    Finland
    #2
    Light is same, but the OOF area is decreased as compared to the same aperture on a full-frame camera.

    Nitpick: a sentence with a paranthesis should also work if you take the paranthesis out.
    Correct usage would be "so my f1.7 20mm is 40mm (equivalent to 35mm)".
     
  3. G.T. thread starter macrumors 6502a

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    Jul 12, 2008
    #3
    OK thanks thats good to know. So I am getting the benefit from f1.7 for low light.
     
  4. madmaxmedia macrumors 68030

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    Dec 17, 2003
    Location:
    Los Angeles, CA
    #4
    Just to add, you are roughly correct about bokeh too.

    The other way of saying it, is that your DOF will still be roughly of that of a 20mm lens.
     
  5. G.T. thread starter macrumors 6502a

    Joined:
    Jul 12, 2008
    #5
    ok, well the other reason for asking is so I know I'm actually getting what I though I'd paid for, I knew about doubling focal length as sensor size is small etc but when a few people started to say different things about aperture values I needed to check, as I want a new lens (I only have 20mm prime and while mostly good I do want a zoom lens). So was like if f-stop was to be doubled and I got a 14-45 f3.5-5.6 then the minimum would be like f7 which would really not help in low light, so was looking at more expensive lenses.

    But anyway glad this is not the case, I did wonder as letting the same light in should not change just cause the sensor size is different.
     
  6. Westside guy macrumors 601

    Westside guy

    Joined:
    Oct 15, 2003
    Location:
    The soggy side of the Pacific NW
    #6
    The "focal length" differences are strictly a function of sensor size. The 4/3 and m4/3 sensors are half the size of a 35mm frame, so what's really happening is the m4/3 sensor is just intercepting the middle part of that image. If the sensor of that camera were made magically larger, and you were able to use that same lens (and assuming that lens wouldn't physically vignette) - the image would then look as if you'd "zoomed out" somewhat because that larger sensor would then be able to capture more of the image the lens focussed at the focal plane.

    Most of the time people use the term "crop factor" to refer to this effect. 4/3 cameras have a 2x crop factor; Canon's smaller sensor cameras have a 1.6x crop factor; Nikon's smaller sensor cameras have a 1.5x crop factor; and of course full frame cameras have no crop factor (1x).
     
  7. toxic macrumors 68000

    Joined:
    Nov 9, 2008
    #7
    bokeh is a lens quality, like barrel distortion or resolution. a lens can have smooth, rough, swirly, or some other type of bokeh. it never has more or less.

    the f-ratio has a consistent definition. f/2 is f/2 regardless of the camera format. it's defined that way so you never have to worry about what focal length or aperture or camera you're using to determine the right exposure.

    depth of field for the same framing increases as sensor size decreases. when going from 35mm to APS-C, you lose approximately 1 1/3 stops of DoF, i.e. 32mm f/2.5 on APS-C yields the same image as 50mm f/4. 4/3 format is a 1.3 crop of APS-C, so you lose another ~2/3 stop, so for the example above, you'd need a 25mm f/2. the important thing to remember is that this is just coincidence. f/2.2 on 4/3 is not the same as f/4.5 on 35mm, it simply means that DoF happens to be equivalent at those f-stops when standing in the same location and framing the same way.
     
  8. G.T. thread starter macrumors 6502a

    Joined:
    Jul 12, 2008
    #8
    Thanks that makes so much more sense, so my lens shot at f1.7 will appear the same as f3.4 but only in how much the background is blurred. F1.7 will let in the same light on my camera as a lens with that f-stop on a 35mm format camera.
     

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