The stupid, STUPID 4/3rds versus FF lens B.S.

Discussion in 'Digital Photography' started by RichA, Oct 21, 2010.

  1. RichA

    RichA Guest

    That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
    This is B.S. The amount of light falling on a given area on the
    sensor is the SAME no matter what size a sensor is. It has NOTHING to
    do with noise levels and EVERYTHING to do with exposure and aperture.
    The lens doesn't magically change its aperture when it is put on a
    FF. A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
    to need the SAME exposure on a FF at the SAME ISO to achieve the same
    illumination level from the sensor. If you don't believe this, take
    the SAME lens and shoot with both cameras at the same f-stop and
    shutter speed. The images will be the same as far as illumination
    levels are concerned, but the FF will have a wider field showing and
    will have less image noise.
     
    RichA, Oct 21, 2010
    #1
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  2. "RichA" <> wrote in message
    news:...
    > That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
    > This is B.S. The amount of light falling on a given area on the
    > sensor is the SAME no matter what size a sensor is. It has NOTHING to
    > do with noise levels and EVERYTHING to do with exposure and aperture.
    > The lens doesn't magically change its aperture when it is put on a
    > FF. A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
    > to need the SAME exposure on a FF at the SAME ISO to achieve the same
    > illumination level from the sensor. If you don't believe this, take
    > the SAME lens and shoot with both cameras at the same f-stop and
    > shutter speed. The images will be the same as far as illumination
    > levels are concerned, but the FF will have a wider field showing and
    > will have less image noise.


    The signal-to-noise ratio of the image is determined by the number of
    photons (assuming a low read noise). Taking the f/4 lens on full frame,
    then roughly APS_C has half the area, and therefore requires twice the
    number of photons per unit area, and the 4/3 has a quarter of the area, so
    about four times the photons per unit area. So to capture the same image
    with the same SNR, the smaller sensor requires the larger aperture lens.

    David
     
    David J Taylor, Oct 22, 2010
    #2
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  3. RichA

    Robert Coe Guest

    On Thu, 21 Oct 2010 15:25:04 -0700 (PDT), RichA <> wrote:
    : That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
    : This is B.S. The amount of light falling on a given area on the
    : sensor is the SAME no matter what size a sensor is. It has NOTHING to
    : do with noise levels and EVERYTHING to do with exposure and aperture.
    : The lens doesn't magically change its aperture when it is put on a
    : FF. A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
    : to need the SAME exposure on a FF at the SAME ISO to achieve the same
    : illumination level from the sensor. If you don't believe this, take
    : the SAME lens and shoot with both cameras at the same f-stop and
    : shutter speed. The images will be the same as far as illumination
    : levels are concerned, but the FF will have a wider field showing and
    : will have less image noise.

    I guess there's nothing wrong with your argument, but you forgot to stuff the
    strawman first. I haven't heard anybody make the claim you're trying to
    debunk. It's focal length, not f-stop, that people tend to quote in terms of
    its "FF equivalent". I think that's silly too, but it isn't "wrong": a lens of
    a given focal length really does produce different results, depending on the
    sensor size of the camera on which it's used. Your point, which everyone
    accepts AFAIK, seems to be that a given f-stop has the same effect everywhere.
    Is there some subtle issue that's sailing over my head here?

    Bob
     
    Robert Coe, Oct 23, 2010
    #3
  4. RichA

    Rich Guest

    On Oct 23, 5:50 pm, Paul Furman <> wrote:
    > RichA wrote:
    > > That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
    > > This is B.S.  The amount of light falling on a given area on the
    > > sensor is the SAME no matter what size a sensor is.  It has NOTHING to
    > > do with noise levels and EVERYTHING to do with exposure and aperture.
    > > The lens doesn't magically change its aperture when it is put on a
    > > FF.  A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
    > > to need the SAME exposure on a FF at the SAME ISO to achieve the same
    > > illumination level from the sensor.  If you don't believe this, take
    > > the SAME lens and shoot with both cameras at the same f-stop and
    > > shutter speed.  The images will be the same as far as illumination
    > > levels are concerned, but the FF will have a wider field showing and
    > > will have less image noise.

    >
    > M4/3 is half the width, a quarter the area of FX. A quarter the photons,


    Photons per pixel is government solely by lens focal ratio. That is
    all that dictates exposure.
     
    Rich, Oct 24, 2010
    #4
  5. "Rich" <> wrote in message
    news:...
    []
    > Photons per pixel is government solely by lens focal ratio. That is
    > all that dictates exposure.


    With a given f/number and focal length, the photons per pixel depends on
    the pixel area as well. Larger pixels capture more photons. Bear in mind
    that different pixels on different sensors will saturate at a different
    number of photons, as the well size is different.

    David
     
    David J Taylor, Oct 24, 2010
    #5
  6. RichA

    Robert Coe Guest

    On Sat, 23 Oct 2010 18:59:31 -0700 (PDT), Rich <> wrote:
    : On Oct 23, 5:50 pm, Paul Furman <> wrote:
    : > RichA wrote:
    : > > That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
    : > > This is B.S.  The amount of light falling on a given area on the
    : > > sensor is the SAME no matter what size a sensor is.  It has NOTHING to
    : > > do with noise levels and EVERYTHING to do with exposure and aperture.
    : > > The lens doesn't magically change its aperture when it is put on a
    : > > FF.  A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
    : > > to need the SAME exposure on a FF at the SAME ISO to achieve the same
    : > > illumination level from the sensor.  If you don't believe this, take
    : > > the SAME lens and shoot with both cameras at the same f-stop and
    : > > shutter speed.  The images will be the same as far as illumination
    : > > levels are concerned, but the FF will have a wider field showing and
    : > > will have less image noise.
    : >
    : > M4/3 is half the width, a quarter the area of FX. A quarter the photons,
    :
    : Photons per pixel is government solely by lens focal ratio. That is
    : all that dictates exposure.

    Government by lens focal ratio. I like that. It's a lot better than what we'll
    have under the Tea Party.

    Bob
     
    Robert Coe, Oct 24, 2010
    #6
  7. RichA

    Robert Coe Guest

    On Sat, 23 Oct 2010 14:50:35 -0700, Paul Furman <> wrote:
    : RichA wrote:
    : > That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
    : > This is B.S. The amount of light falling on a given area on the
    : > sensor is the SAME no matter what size a sensor is. It has NOTHING to
    : > do with noise levels and EVERYTHING to do with exposure and aperture.
    : > The lens doesn't magically change its aperture when it is put on a
    : > FF. A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
    : > to need the SAME exposure on a FF at the SAME ISO to achieve the same
    : > illumination level from the sensor. If you don't believe this, take
    : > the SAME lens and shoot with both cameras at the same f-stop and
    : > shutter speed. The images will be the same as far as illumination
    : > levels are concerned, but the FF will have a wider field showing and
    : > will have less image noise.
    :
    : M4/3 is half the width, a quarter the area of FX.

    A third, not a quarter. You didn't take into account the difference in aspect
    ratios (4/3 for M4/3 vs 3/2 for FX).

    Bob
     
    Robert Coe, Oct 24, 2010
    #7
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