Lens resolution versus pixel density

Discussion in 'Digital Photography' started by Rich, Dec 16, 2006.

  1. Rich

    Rich Guest

    There is alot of acrimony over exactly how much resolution a lens will
    support and how many megapixels a camera could be. So assuming you're
    only talking about the centre of the field using
    a lens of high quality stopped down what pixel density could it
    support?
    According to Olympus, their pro lenses will support a pixel density (if
    it existed) of 22 megs on their 4/3rds sensors.
    Rich, Dec 16, 2006
    #1
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  2. Rich

    Bob Williams Guest

    Rich wrote:

    > There is alot of acrimony over exactly how much resolution a lens will
    > support and how many megapixels a camera could be. So assuming you're
    > only talking about the centre of the field using
    > a lens of high quality stopped down what pixel density could it
    > support?
    > According to Olympus, their pro lenses will support a pixel density (if
    > it existed) of 22 megs on their 4/3rds sensors.
    >


    A 4/3 sensor is 13.5mm x 18.0mm or 243 million square microns in area.
    If this area contained 22 million pixels, each pixel would have an area
    of 11.0 square microns or 3.32 microns on a side.
    Many, if not most, P/S cameras have pixel sizes smaller than that.
    So a lens that will support 22 MP on a 4/3 type sensor is no big deal.

    A 4/3 sensor could "easily" be made to contain 22 MP if that was
    desirable. The problem is that the noise level would be comparable to
    that from a P/S camera. This would negate the big advantage that DSLRs
    have over P/S cameras, i.e. low noise and high signal/noise ratio.
    Bob Williams
    Bob Williams, Dec 17, 2006
    #2
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  3. Bob Williams <> writes:

    >> According to Olympus, their pro lenses will support a pixel density (if
    >> it existed) of 22 megs on their 4/3rds sensors.


    >A 4/3 sensor is 13.5mm x 18.0mm or 243 million square microns in area.
    >If this area contained 22 million pixels, each pixel would have an area
    >of 11.0 square microns or 3.32 microns on a side.


    So far so good.

    >Many, if not most, P/S cameras have pixel sizes smaller than that.
    >So a lens that will support 22 MP on a 4/3 type sensor is no big deal.


    But not here. P/S cameras do have small pixels, but they also have
    small sensors. A typical sensor width is about 7 mm; many are smaller
    yet. In order to keep the same field of view, the lens focal length is
    scaled down as well - so a "normal" lens is about 10 mm focal length
    instead of 50 mm.

    And when you scale down the focal length by a factor of 5 without
    changing the field of view, *the aberrations scale down as well*, so you
    automatically get higher resolution to go along with the smaller sensor.
    (That applies only to aberrations, not diffraction).

    Now, a normal lens for the 4/3 system would be about 25 mm focal length,
    not 10 mm. So, at the same f/number, its aberrations can be expected to
    be about 2.5 times larger in absolute size. Keeping the
    aberration-caused blur below the pixel size is a much bigger challenge
    when the focal length and image circle is 2.5 times larger.

    Dave
    Dave Martindale, Dec 18, 2006
    #3
  4. Rich

    Bob Williams Guest

    Dave Martindale wrote:
    > Bob Williams <> writes:
    >
    >
    >>>According to Olympus, their pro lenses will support a pixel density (if
    >>>it existed) of 22 megs on their 4/3rds sensors.

    >
    >
    >>A 4/3 sensor is 13.5mm x 18.0mm or 243 million square microns in area.
    >>If this area contained 22 million pixels, each pixel would have an area
    >>of 11.0 square microns or 3.32 microns on a side.

    >
    >
    > So far so good.
    >
    >
    >>Many, if not most, P/S cameras have pixel sizes smaller than that.
    >>So a lens that will support 22 MP on a 4/3 type sensor is no big deal.

    >
    >
    > But not here. P/S cameras do have small pixels, but they also have
    > small sensors. A typical sensor width is about 7 mm; many are smaller
    > yet. In order to keep the same field of view, the lens focal length is
    > scaled down as well - so a "normal" lens is about 10 mm focal length
    > instead of 50 mm.
    >
    > And when you scale down the focal length by a factor of 5 without
    > changing the field of view, *the aberrations scale down as well*, so you
    > automatically get higher resolution to go along with the smaller sensor.
    > (That applies only to aberrations, not diffraction).
    >
    > Now, a normal lens for the 4/3 system would be about 25 mm focal length,
    > not 10 mm. So, at the same f/number, its aberrations can be expected to
    > be about 2.5 times larger in absolute size. Keeping the
    > aberration-caused blur below the pixel size is a much bigger challenge
    > when the focal length and image circle is 2.5 times larger.



    That is certainly true.
    But Oly claims that their lens CAN support 22MP on a 4/3 type sensor.
    Yet, they do not offer such a product even in the midst of a crazy MP
    war where, I suspect lots of folks interested in bragging rights, would
    bust the doors down to own a 22MP camera!!! But Oly knows that the image
    quality from such a sensor would suffer and the S/N ratio would be
    similar to a modestly priced P/S camera. Therefore, IMHO, that is why
    they restrain themselves from making such an offering.
    Bob
    Bob Williams, Dec 18, 2006
    #4
  5. Bob Williams <> writes:

    >That is certainly true.
    >But Oly claims that their lens CAN support 22MP on a 4/3 type sensor.


    My point was that a lens with resolution to match a ~3 um pixel pitch
    sensor *and* cover an 18 mm wide frame is nothing to sneeze at. It's
    much more significant than covering a sensor that's only 40% as wide
    with a lens of 40% of the focal length at the same pixel pitch.

    Another way to look at it: although the 4/3 lens and the
    small-sensor-digicam lens have the same resolution in terms of lp/mm at
    the image plane, the resolution in terms of line pairs per *picture
    height* is 2.5 times (or more) greater for the 4/3 lens.

    >Yet, they do not offer such a product even in the midst of a crazy MP
    >war where, I suspect lots of folks interested in bragging rights, would
    >bust the doors down to own a 22MP camera!!! But Oly knows that the image
    >quality from such a sensor would suffer and the S/N ratio would be
    >similar to a modestly priced P/S camera. Therefore, IMHO, that is why
    >they restrain themselves from making such an offering.


    That, and the difficulty in making a 22 MP sensor and the supporting
    electronics. It does seem like a good tradeoff.

    I find myself wishing that I could still buy a good-quality 4 MP
    point&shoot camera, instead of 6 or 7 MP.

    Dave
    Dave Martindale, Dec 18, 2006
    #5
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