Circle of Confusion

Discussion in 'Digital Photography' started by Donald Gray, Jul 3, 2004.

  1. Donald Gray

    Donald Gray Guest

    I saw this being discussed in an earlier thread...

    FWIW, here are my thoughts on it..

    When I studied photography in an other life time, (50 years ago, so my
    memory ain't so good these days), I under stood that the CoC was not a
    fixed size but varied according to the viewing distance and actuity of
    the viewers eyes.

    I seem to remember ...

    .... The CoC is the point when dot or object can no longer be
    detected/defined by the eye because of the distance of the eye to the
    object/dot. It becomes a 'circle of a confused' image in the eye. When
    applied to a lens and film (or digital), I guess it is the smallest
    dot that the combination of quality of glass (actuity) and the
    resolution (grain or pixel) that the image of the dot/object falls
    upon.

    .... The smallest dot that can be detected by the eye with 'average,
    normal' eye sight, the CoC on white paper, under average lighting
    conditions could be expressed as 1/500 of an inch when viewed from 36
    inches.

    So, a dot 3 inches in diameter on a white sheet is huge when viewed
    from 3 feet but when viewed from several hundred yards (metres) away,
    the do cannot be resolved by the unaided human eye.

    my tuppence worth...

    The other definition of the "Circle of Confusion" is what politician
    run all day....
    --
    Donald Gray
    Putting ODCOMBE on the Global Village Map!
    www.odcombe.demon.co.uk
    You do not have to email me, but if you wish to...
    Please remove the SafetyPin from my email address first
    Thanks
     
    Donald Gray, Jul 3, 2004
    #1
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  2. Donald Gray <> wrote in
    news::

    > I saw this being discussed in an earlier thread...
    >
    > FWIW, here are my thoughts on it..
    >
    > When I studied photography in an other life time, (50 years ago, so my
    > memory ain't so good these days), I under stood that the CoC was not a
    > fixed size but varied according to the viewing distance and actuity of
    > the viewers eyes.
    >
    > I seem to remember ...
    >
    > ... The CoC is the point when dot or object can no longer be
    > detected/defined by the eye because of the distance of the eye to the
    > object/dot. It becomes a 'circle of a confused' image in the eye. When
    > applied to a lens and film (or digital), I guess it is the smallest
    > dot that the combination of quality of glass (actuity) and the
    > resolution (grain or pixel) that the image of the dot/object falls
    > upon.
    >
    > ... The smallest dot that can be detected by the eye with 'average,
    > normal' eye sight, the CoC on white paper, under average lighting
    > conditions could be expressed as 1/500 of an inch when viewed from 36
    > inches.
    >
    > So, a dot 3 inches in diameter on a white sheet is huge when viewed
    > from 3 feet but when viewed from several hundred yards (metres) away,
    > the do cannot be resolved by the unaided human eye.
    >
    > my tuppence worth...


    Okay, to clarify a little:

    A "Circle of Confusion" is basically an artifact of focusing light
    through a lens. When a lens focuses onto a surface, such as film or a
    digital sensor, it is converging the light exiting the lens from a cone
    down to a point. The point is supposedly the area of perfect focus, but
    there really is no such thing. Part of the reason is, different portions of
    a lens have different affects, and different wavelengths of light (colors)
    get altered more than others. Just like a prism, only circular instead of
    the bands we're used to.

    If the focus point is, for instance, behind the surface
    (film/sensor), then the surface is intersecting the cone before it reaches
    the point, in essence chopping off the tip. The resulting image on the
    surface is a circle of confusion, in this example a very broad one. If the
    surface is as close to that focal point as physically possible, the CoC is
    therefore very small. It is possible for it to be smaller than the
    resolution of the image medium (film grain or digital pixels), in which
    case the resolution limits are set by the medium. If the smallest CoC is
    larger than the resolution of the media, the limit of resolution is set by
    the lens itself.

    There are lots of factors, such as aspherical lenses, whether the
    image passes directly through the lens axis (the highest acuity area,
    sometimes called the 'sweet spot'), chromatic aberration (the prism
    effect), diffraction limits of the aperture, and so on. So CoC is a
    constantly changing thing. To say nothing whatsoever of the fact that it
    relies on a very fine point at a precise distance - anything else is
    rendered differently. So with a short depth-of-field, your background
    exhibits much larger CoCs than your focused subject, giving that nice soft
    mushy background effect.

    CoC does relate, in a small way, to eyesight, because our eyes have
    their own lenses. But generally, it is used to refer to cameras and such.
    Resolving power of the human eye is dependent on a lot of things other than
    the performance of our natural lenses (and cornea, and aqueous humor). For
    instance, a remarkably small circle can be resolved if it's bright enough -
    that's how we can see stars at night, which cannot effectively be measured
    'across' in arc-seconds (the unit of measurement usually used, pretty much
    the same thing as 'field of view', just very small increments). Contrast
    plays an enormous role in our resolving ability, which is why lenses are
    measured in "line pairs per millimeter" - the contrast of black and white
    lines gives the best representation of resolution.


    > The other definition of the "Circle of Confusion" is what politician
    > run all day...


    True! And don't forget the Department of Motor Vehicles...


    - Al.

    --
    To reply, insert dash in address to separate G and I in the domain
     
    Al Denelsbeck, Jul 3, 2004
    #2
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  3. Donald Gray

    Guest

    Archived from Donald Gray <> on Sat, 03
    Jul 2004 12:11:41 +0100:

    >I saw this being discussed in an earlier thread...

    [good stuff]

    Are you all Gray or only 18%? ;-) <Sorry. Couldn't resist> Cheers.
     
    , Jul 3, 2004
    #3
  4. Donald Gray

    Donald Gray Guest

    On Sat, 03 Jul 2004 17:49:28 GMT, wrote:

    >Archived from Donald Gray <> on Sat, 03
    >Jul 2004 12:11:41 +0100:
    >
    >>I saw this being discussed in an earlier thread...

    >[good stuff]
    >
    >Are you all Gray or only 18%? ;-) <Sorry. Couldn't resist> Cheers.
    >


    100% Mid Gray!!!!! (#808080 - RGB: 128,128,128)

    Did you see my 100% Gray Scale at:
    www.websilk.co.uk/digital ?
    --
    Donald Gray
    Putting ODCOMBE on the Global Village Map!
    www.odcombe.demon.co.uk
    You do not have to email me, but if you wish to...
    Please remove the SafetyPin from my email address first
    Thanks
     
    Donald Gray, Jul 3, 2004
    #4
  5. Donald Gray

    Phil Wheeler Guest

    New name for this newsgroup? <g>

    Phil
     
    Phil Wheeler, Jul 4, 2004
    #5
  6. Donald Gray

    Frank ess Guest

    Phil Wheeler wrote:
    > New name for this newsgroup? <g>
    >
    > Phil


    If there can be such a thing as
    "Obtuse Circle Of Confusion"
    yes.
     
    Frank ess, Jul 4, 2004
    #6
  7. Donald Gray

    Guest

    Archived from Donald Gray <> on Sat, 03
    Jul 2004 20:29:32 +0100:

    >On Sat, 03 Jul 2004 17:49:28 GMT, wrote:
    >
    >>Archived from Donald Gray <> on Sat, 03
    >>Jul 2004 12:11:41 +0100:
    >>
    >>>I saw this being discussed in an earlier thread...

    >>[good stuff]
    >>
    >>Are you all Gray or only 18%? ;-) <Sorry. Couldn't resist> Cheers.
    >>

    >
    >100% Mid Gray!!!!! (#808080 - RGB: 128,128,128)
    >
    >Did you see my 100% Gray Scale at:
    >www.websilk.co.uk/digital ?


    I did now. Fun site. Thanks for the Gray Scale. I need to buy a new
    monitor. :)

    Vic
     
    , Jul 4, 2004
    #7
  8. Donald Gray

    Donald Gray Guest

    On Sat, 03 Jul 2004 23:47:52 GMT, wrote:

    >Archived from Donald Gray <> on Sat, 03
    >Jul 2004 20:29:32 +0100:
    >
    >>On Sat, 03 Jul 2004 17:49:28 GMT, wrote:
    >>
    >>>Archived from Donald Gray <> on Sat, 03
    >>>Jul 2004 12:11:41 +0100:
    >>>
    >>>>I saw this being discussed in an earlier thread...
    >>>[good stuff]
    >>>
    >>>Are you all Gray or only 18%? ;-) <Sorry. Couldn't resist> Cheers.
    >>>

    >>
    >>100% Mid Gray!!!!! (#808080 - RGB: 128,128,128)
    >>
    >>Did you see my 100% Gray Scale at:
    >>www.websilk.co.uk/digital ?

    >
    >I did now. Fun site. Thanks for the Gray Scale. I need to buy a new
    >monitor. :)
    >
    >Vic


    Glad you liked it Vic, I hope you find the Step wedge useful. Thanks
    for the comment.

    Regards
    --
    Donald Gray
    Putting ODCOMBE on the Global Village Map!
    www.odcombe.demon.co.uk
    You do not have to email me, but if you wish to...
    Please remove the SafetyPin from my email address first
    Thanks
     
    Donald Gray, Jul 4, 2004
    #8
  9. "Frank ess" <> wrote in message
    news:drHFc.22465$...
    > Phil Wheeler wrote:
    > > New name for this newsgroup? <g>
    > >
    > > Phil

    >
    > If there can be such a thing as
    > "Obtuse Circle Of Confusion"
    > yes.

    ....

    No, no, no. The "Circle of Confusion" is a high tech device (much like
    Maxwell
    Smart's Cone of Silence) employed by various members of this newsgroup
    (like George Preddy), some more than others (like George Preddy), to prevent
    unwanted ideas from being perceived and entering into their consciousness.

    It sells quite well into the "Blind Faith" and "Unexamined Dogma" markets.

    Use at your own risk.

    (Side effects may include: a tendency for others to avoid you, headaches,
    hair loss, insomnia, paranoia, bad breath, sexual side effects, carpal
    tunnel
    syndrome, myopia, hypertension, and weight gain. Do not use in conjunction
    with alcohol, cannabis, or mood altering drugs, since combined use could
    lead to unpredictable new thoughts. Always consult your Authority Figure
    before using Circle of Confusion. Discontinue immediately on the formation
    of rational thoughts.)


    --
    Dan (Woj...) dmaster at lucent dot com
    ----------------------------------
    "What can you see / On the horizon?
    Why do the white gulls call?
    Across the sea / A pale moon rises.
    The ships have come / To carry you home.
    And all will turn to silver glass.
    A light on the water / All souls pass."
     
    Dan Wojciechowski, Jul 7, 2004
    #9
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