Depth of field

Discussion in 'Digital Photography' started by Armando, Nov 18, 2005.

  1. Armando

    Armando Guest

    Apologies if this is a rehash, I searched on all the related terms I could
    think of first...

    In a "real" camera (sorry about that), the f-stop setting of the lens
    affects the DOF because of the physical size of the aperture. How is
    "f-stop" handled on a digital camera? My guess has always been that it's
    just a electrical tweak to the overall brightness of the image, and not an
    actual "sphincter" in the lens. A friend has suggested that they could
    actually use an LCD shutter, with concentric rings set to transparent or
    opaque, to get an actual physical-size thing going, with real DOF.

    I confess I've not tried any actual tests to see for myself, but maybe
    there's a discussion here while I'm getting around to it...

    Armando
    Armando, Nov 18, 2005
    #1
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  2. Armando

    223rem Guest

    Armando wrote:
    > Apologies if this is a rehash, I searched on all the related terms I could
    > think of first...
    >
    > In a "real" camera (sorry about that), the f-stop setting of the lens
    > affects the DOF because of the physical size of the aperture. How is
    > "f-stop" handled on a digital camera? My guess has always been that it's
    > just a electrical tweak to the overall brightness of the image, and not an
    > actual "sphincter" in the lens.


    Digital SLRs use same lenses as film SLRs!

    Non SLR digital cameras also should use mechanical
    iris (DOF modulation would not be possible by simply
    simply modulating the amplification of the sensor signal).

    I believe that What digital cameras dont have is mechanical
    shutters--it is done electronically.
    223rem, Nov 18, 2005
    #2
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  3. Armando

    Scott W Guest

    223rem wrote:
    > Armando wrote:
    > > Apologies if this is a rehash, I searched on all the related terms I could
    > > think of first...
    > >
    > > In a "real" camera (sorry about that), the f-stop setting of the lens
    > > affects the DOF because of the physical size of the aperture. How is
    > > "f-stop" handled on a digital camera? My guess has always been that it's
    > > just a electrical tweak to the overall brightness of the image, and not an
    > > actual "sphincter" in the lens.

    >
    > Digital SLRs use same lenses as film SLRs!
    >
    > Non SLR digital cameras also should use mechanical
    > iris (DOF modulation would not be possible by simply
    > simply modulating the amplification of the sensor signal).
    >
    > I believe that What digital cameras dont have is mechanical
    > shutters--it is done electronically.


    In fact digital cameras also have shutters and need them, otherwise you
    get blooming.
    There is an electronic aspect to it but you do need a shutter, which is
    what wears out first in most DSLRs.

    Scott
    Scott W, Nov 18, 2005
    #3
  4. Armando wrote:
    > Apologies if this is a rehash, I searched on all the related terms I
    > could think of first...
    >
    > In a "real" camera (sorry about that), the f-stop setting of the lens
    > affects the DOF because of the physical size of the aperture. How is
    > "f-stop" handled on a digital camera? My guess has always been that
    > it's just a electrical tweak to the overall brightness of the image,
    > and not an actual "sphincter" in the lens. A friend has suggested
    > that they could actually use an LCD shutter, with concentric rings
    > set to transparent or opaque, to get an actual physical-size thing
    > going, with real DOF.
    > I confess I've not tried any actual tests to see for myself, but maybe
    > there's a discussion here while I'm getting around to it...
    >
    > Armando


    Same in digital as in silver based cameras. There is one trick however.
    Just as 35mm had the half frame, digital has various sized sensors. So you
    will get a little more DOF with the typical digital using a 1.6 factor
    sensor (that is the sensor is 1/1.6 the area of a film camera, a little
    larger than half frame 35mm silver-film camera.

    --
    Joseph Meehan

    Dia duit
    Joseph Meehan, Nov 18, 2005
    #4
  5. Armando

    Lorem Ipsum Guest

    "Armando" <> wrote in message
    news:RNcff.2846$...
    > Apologies if this is a rehash, I searched on all the related terms I could
    > think of first...
    >
    > In a "real" camera (sorry about that), the f-stop setting of the lens
    > affects the DOF because of the physical size of the aperture. How is
    > "f-stop" handled on a digital camera? My guess has always been that it's
    > just a electrical tweak to the overall brightness of the image, and not an
    > actual "sphincter" in the lens. A friend has suggested that they could
    > actually use an LCD shutter, with concentric rings set to transparent or
    > opaque, to get an actual physical-size thing going, with real DOF.


    Digital cameras use real physical aperture/diaphragms, just like 'real'
    cameras.
    Lorem Ipsum, Nov 18, 2005
    #5
  6. >In a "real" camera (sorry about that), the f-stop setting of the lens
    >affects the DOF because of the physical size of the aperture. How is
    >"f-stop" handled on a digital camera? My guess has always been that it's
    >just a electrical tweak to the overall brightness of the image, and not an
    >actual "sphincter" in the lens. A friend has suggested that they could
    >actually use an LCD shutter, with concentric rings set to transparent or
    >opaque, to get an actual physical-size thing going, with real DOF.


    It depends which kind of camera you have. Certainly dSLR cameras use
    a real aperture. I believe that any camera that lets you set the
    aperture has a real aperture and it's not simply a computer trick, but
    I suppose someone might have manufactured a camera with a
    pseudo-aperture.

    What kind of camera do you have?

    The shutter is a different matter. Many digicams don't have a real
    shutter that opens and closes.

    -Joel

    ----------------------------------------------------------------------------
    Free 35mm lens & digital camera reviews: http://www.exc.com/photography
    ----------------------------------------------------------------------------
    Dr. Joel M. Hoffman, Nov 18, 2005
    #6
  7. Armando

    Shawn Hirn Guest

    In article <RNcff.2846$>,
    "Armando" <> wrote:

    > Apologies if this is a rehash, I searched on all the related terms I could
    > think of first...
    >
    > In a "real" camera (sorry about that), the f-stop setting of the lens
    > affects the DOF because of the physical size of the aperture. How is
    > "f-stop" handled on a digital camera? My guess has always been that it's
    > just a electrical tweak to the overall brightness of the image, and not an
    > actual "sphincter" in the lens. A friend has suggested that they could
    > actually use an LCD shutter, with concentric rings set to transparent or
    > opaque, to get an actual physical-size thing going, with real DOF.


    Its the same concept regardless of the type of recording medium, except
    that the depth of field range is different than 35mm film cameras
    because of the different size ccd area. The principles of optics (which
    depth of field relies upon) do not change just because one replaces film
    with a CCD.
    Shawn Hirn, Nov 18, 2005
    #7
  8. Shawn Hirn <> writes:

    > In article <RNcff.2846$>,
    > "Armando" <> wrote:
    >
    >> Apologies if this is a rehash, I searched on all the related terms I could
    >> think of first...
    >>
    >> In a "real" camera (sorry about that), the f-stop setting of the lens
    >> affects the DOF because of the physical size of the aperture. How is
    >> "f-stop" handled on a digital camera? My guess has always been that it's
    >> just a electrical tweak to the overall brightness of the image, and not an
    >> actual "sphincter" in the lens. A friend has suggested that they could
    >> actually use an LCD shutter, with concentric rings set to transparent or
    >> opaque, to get an actual physical-size thing going, with real DOF.

    >
    > Its the same concept regardless of the type of recording medium, except
    > that the depth of field range is different than 35mm film cameras
    > because of the different size ccd area. The principles of optics (which
    > depth of field relies upon) do not change just because one replaces film
    > with a CCD.


    Are you not contradicting yourself there?

    Depth of field at a given distance is determined by three parameters:
    focal length, aperture, and circle of confusion. The first two are
    determined by the optics. The circle of confusion is a somewhat
    subjective property, and is a function of the required sharpness in
    the final image and the size of the recording medium. The image is
    perfectly focused only at one exact distance. The depth of field is
    the range in which the focal blur is too small to be perceptible.

    A neat DoF calculator is available at http://dofmaster.com/dofjs.html.

    --
    Måns Rullgård
    =?iso-8859-1?q?M=E5ns_Rullg=E5rd?=, Nov 18, 2005
    #8
  9. Måns Rullgård <> writes:

    > Shawn Hirn <> writes:
    >
    >> In article <RNcff.2846$>,
    >> "Armando" <> wrote:
    >>
    >>> Apologies if this is a rehash, I searched on all the related terms I could
    >>> think of first...
    >>>
    >>> In a "real" camera (sorry about that), the f-stop setting of the lens
    >>> affects the DOF because of the physical size of the aperture. How is
    >>> "f-stop" handled on a digital camera? My guess has always been that it's
    >>> just a electrical tweak to the overall brightness of the image, and not an
    >>> actual "sphincter" in the lens. A friend has suggested that they could
    >>> actually use an LCD shutter, with concentric rings set to transparent or
    >>> opaque, to get an actual physical-size thing going, with real DOF.

    >>
    >> Its the same concept regardless of the type of recording medium, except
    >> that the depth of field range is different than 35mm film cameras
    >> because of the different size ccd area. The principles of optics (which
    >> depth of field relies upon) do not change just because one replaces film
    >> with a CCD.

    >
    > Are you not contradicting yourself there?


    Sorry, you're not.

    --
    Måns Rullgård
    =?iso-8859-1?q?M=E5ns_Rullg=E5rd?=, Nov 18, 2005
    #9
  10. Måns Rullgård wrote:
    > Shawn Hirn <> writes:
    >
    >> In article <RNcff.2846$>,
    >> "Armando" <> wrote:
    >>
    >>> Apologies if this is a rehash, I searched on all the related terms
    >>> I could think of first...
    >>>
    >>> In a "real" camera (sorry about that), the f-stop setting of the
    >>> lens affects the DOF because of the physical size of the aperture.
    >>> How is "f-stop" handled on a digital camera? My guess has always
    >>> been that it's just a electrical tweak to the overall brightness of
    >>> the image, and not an actual "sphincter" in the lens. A friend has
    >>> suggested that they could actually use an LCD shutter, with
    >>> concentric rings set to transparent or opaque, to get an actual
    >>> physical-size thing going, with real DOF.

    >>
    >> Its the same concept regardless of the type of recording medium,
    >> except that the depth of field range is different than 35mm film
    >> cameras because of the different size ccd area. The principles of
    >> optics (which depth of field relies upon) do not change just because
    >> one replaces film with a CCD.

    >
    > Are you not contradicting yourself there?
    >
    > Depth of field at a given distance is determined by three parameters:
    > focal length, aperture, and circle of confusion.


    I don't think he is contradicting himself. Generally we compare the DOF
    of two photographs of the same subject. Most digital cameras have a smaller
    recording area than a 35mm so to capture the same subject at the same
    distance the focal length must be changed. In a typical situation you would
    be comparing images from a 35mm with a 50mm lens and a digital with a 32 mm
    lens.

    > The first two are
    > determined by the optics. The circle of confusion is a somewhat
    > subjective property, and is a function of the required sharpness in
    > the final image and the size of the recording medium. The image is
    > perfectly focused only at one exact distance. The depth of field is
    > the range in which the focal blur is too small to be perceptible.
    >
    > A neat DoF calculator is available at http://dofmaster.com/dofjs.html.


    --
    Joseph Meehan

    Dia duit
    Joseph Meehan, Nov 18, 2005
    #10
  11. "Joseph Meehan" <> writes:

    > Måns Rullgård wrote:
    >> Shawn Hirn <> writes:
    >>
    >>> In article <RNcff.2846$>,
    >>> "Armando" <> wrote:
    >>>
    >>>> Apologies if this is a rehash, I searched on all the related terms
    >>>> I could think of first...
    >>>>
    >>>> In a "real" camera (sorry about that), the f-stop setting of the
    >>>> lens affects the DOF because of the physical size of the aperture.
    >>>> How is "f-stop" handled on a digital camera? My guess has always
    >>>> been that it's just a electrical tweak to the overall brightness of
    >>>> the image, and not an actual "sphincter" in the lens. A friend has
    >>>> suggested that they could actually use an LCD shutter, with
    >>>> concentric rings set to transparent or opaque, to get an actual
    >>>> physical-size thing going, with real DOF.
    >>>
    >>> Its the same concept regardless of the type of recording medium,
    >>> except that the depth of field range is different than 35mm film
    >>> cameras because of the different size ccd area. The principles of
    >>> optics (which depth of field relies upon) do not change just because
    >>> one replaces film with a CCD.

    >>
    >> Are you not contradicting yourself there?
    >>
    >> Depth of field at a given distance is determined by three parameters:
    >> focal length, aperture, and circle of confusion.

    >
    > I don't think he is contradicting himself.


    I already said I was wrong. His mention of film vs. ccd had me
    confused. Both film and sensors come in a variety of sizes, so
    mentioning the technologies serves no direct purpose. I realize that
    film is most commonly 35mm, and digital sensors are generally smaller,
    which is probably why he mentioned the two in the way he did.

    --
    Måns Rullgård
    =?iso-8859-1?q?M=E5ns_Rullg=E5rd?=, Nov 18, 2005
    #11
  12. Armando

    Bill Funk Guest

    On Fri, 18 Nov 2005 20:36:18 GMT, "Joseph Meehan"
    <> wrote:

    >Måns Rullgård wrote:
    >> Shawn Hirn <> writes:
    >>
    >>> In article <RNcff.2846$>,
    >>> "Armando" <> wrote:
    >>>
    >>>> Apologies if this is a rehash, I searched on all the related terms
    >>>> I could think of first...
    >>>>
    >>>> In a "real" camera (sorry about that), the f-stop setting of the
    >>>> lens affects the DOF because of the physical size of the aperture.
    >>>> How is "f-stop" handled on a digital camera? My guess has always
    >>>> been that it's just a electrical tweak to the overall brightness of
    >>>> the image, and not an actual "sphincter" in the lens. A friend has
    >>>> suggested that they could actually use an LCD shutter, with
    >>>> concentric rings set to transparent or opaque, to get an actual
    >>>> physical-size thing going, with real DOF.
    >>>
    >>> Its the same concept regardless of the type of recording medium,
    >>> except that the depth of field range is different than 35mm film
    >>> cameras because of the different size ccd area. The principles of
    >>> optics (which depth of field relies upon) do not change just because
    >>> one replaces film with a CCD.

    >>
    >> Are you not contradicting yourself there?
    >>
    >> Depth of field at a given distance is determined by three parameters:
    >> focal length, aperture, and circle of confusion.

    >
    > I don't think he is contradicting himself. Generally we compare the DOF
    >of two photographs of the same subject. Most digital cameras have a smaller
    >recording area than a 35mm so to capture the same subject at the same
    >distance the focal length must be changed. In a typical situation you would
    >be comparing images from a 35mm with a 50mm lens and a digital with a 32 mm
    >lens.


    And that's with an APS-C sensor size, such as with a DRebel or 20D, or
    close to the Nikon D70.
    With a smaller P&S camera, the focal length would be much smaller, in
    the 10-25mm range, depending on the size of the sensor.

    While the focal length is indeed determined by the optics, the optics
    are chosen to match the sensor.

    --
    Bill Funk
    Replace "g" with "a"
    funktionality.blogspot.com
    Bill Funk, Nov 18, 2005
    #12
  13. "Måns Rullgård" <> wrote in message
    news:...
    [ . . . ]
    >
    > Depth of field at a given distance is determined by three parameters:


    Four or five, actually, depending on how you look at it.


    > focal length, aperture, and circle of confusion.


    Also final magnification and viewing distance (which might or might not be
    regarded as the same thing). These are the things that most depth of field
    calculations tend to ignore. If you add to that the fact that not everyone
    has exactly the same visual acuity, you get still another variable.


    > The first two are
    > determined by the optics. The circle of confusion is a somewhat
    > subjective property, and is a function of the required sharpness in
    > the final image and the size of the recording medium. The image is
    > perfectly focused only at one exact distance.


    And not even that, if "perfectly focused" is taken to mean that a point on
    the subject is represented as a true point at the film plane. That never
    happens, with any lens ever manufactured on this planet. Because of lens
    aberrations, the "plane of best focus" may well be slightly thicker than a
    true plane.


    > The depth of field is
    > the range in which the focal blur is too small to be perceptible.


    Yes, and that changes with final magnification and/or viewing distance.


    >
    > A neat DoF calculator is available at http://dofmaster.com/dofjs.html.


    The problem with most such calculators is that they don't take those other
    two factors into consideration. The circle of confusion is chosen on the
    *assumption* not only of a certain visual acuity, but also a certain final
    magnification and viewing distance. But a 2x3" print viewed at a given
    distance will have noticeably more depth of field than an 11x14" print of
    the same shot at the same distance (assuming a sharp source and neglible
    loss in the enlargement), and the 11x14 viewed at 10 feet will have more
    depth of field than it did at 10 inches.

    Depth of field tables, calculators and engraved lens scales are taken by
    some folks as a kind of precise cosmic truth, but in fact they are such
    rough guides as to be of doubtful usefulness. Still, many people seem to
    enjoy them, and they do little if any harm, so what the heck. ;-)

    Neil
    Neil Harrington, Nov 18, 2005
    #13
  14. Armando

    Armando Guest

    OP here.

    My camera is a Sony DSC-S50. A 2.1 MP beast from a few years back, but it
    still impresses me now and then. It's my first and so far only digital (not
    counting the not-really-serious 640x480 binocu-cam I got as a gift
    recently).

    I never even thought about SLRs when I asked the question! Of course the
    aperture is in the lens, of course there's a mechanical shutter. Duh on me.
    So let me rephrase (or narrow the scope of) my question. In *MY* camera,
    how do they do the "f-stop"? I select it from the GUI, and not by spinning
    a ring on the lens. This is why it feels fake. I did actually try a test
    once, I now recall, but I don't remember seeing much difference with various
    settings.

    Thanks again,

    Armando
    Armando, Nov 19, 2005
    #14
  15. Armando

    Bill Funk Guest

    On Sat, 19 Nov 2005 04:19:42 GMT, "Armando" <> wrote:

    >OP here.
    >
    >My camera is a Sony DSC-S50. A 2.1 MP beast from a few years back, but it
    >still impresses me now and then. It's my first and so far only digital (not
    >counting the not-really-serious 640x480 binocu-cam I got as a gift
    >recently).
    >
    >I never even thought about SLRs when I asked the question! Of course the
    >aperture is in the lens, of course there's a mechanical shutter. Duh on me.
    >So let me rephrase (or narrow the scope of) my question. In *MY* camera,
    >how do they do the "f-stop"? I select it from the GUI, and not by spinning
    >a ring on the lens. This is why it feels fake. I did actually try a test
    >once, I now recall, but I don't remember seeing much difference with various
    >settings.
    >
    >Thanks again,
    >
    >Armando
    >

    I'm not aware of a way to effectively fake an aperture; it requires an
    iris of some sort.
    There are 3 basic methods to control the light in a camera:
    film/sensor speed (the ISO setting), shutter speed, and aperture (the
    f/ stop).
    The ISO setting is basic; the shutter can be faked, but I think all
    but the very cheapest digital cameras use a shutter; the aperture
    can't be faked, there's no way to mimic a variable aperture. The
    variance in the depth of field just can't be faked (at least not
    without a lot of work on the part of a person in an app such as
    Photoshop).
    That you don't use a lens ring to change the aperture in
    aperture-preferred mode doesn't mean anything; the aperture will be
    controlled electronically no matter how you select it. (As will be the
    ISO speed and the shutter speed.)
    Hope this helps.

    --
    Bill Funk
    Replace "g" with "a"
    funktionality.blogspot.com
    Bill Funk, Nov 19, 2005
    #15
  16. Armando

    John Bean Guest

    On Sat, 19 Nov 2005 04:19:42 GMT, "Armando"
    <> wrote:

    >My camera is a Sony DSC-S50. A 2.1 MP beast from a few years back, but it
    >still impresses me now and then. It's my first and so far only digital (not
    >counting the not-really-serious 640x480 binocu-cam I got as a gift
    >recently).
    >
    >I never even thought about SLRs when I asked the question! Of course the
    >aperture is in the lens, of course there's a mechanical shutter. Duh on me.
    >So let me rephrase (or narrow the scope of) my question. In *MY* camera,
    >how do they do the "f-stop"? I select it from the GUI, and not by spinning
    >a ring on the lens. This is why it feels fake. I did actually try a test
    >once, I now recall, but I don't remember seeing much difference with various
    >settings.


    The shutter and diaphagm are normally combined in a camera
    like yours. It's fully open for viewing but when you take a
    picture it first closes fully, then after preparing the
    sensor it *partially* opens to the required f-stop and
    remains there for the required exposure time before closing.
    After the image is saved the camera reconfigures the sensor
    for live video and opens the shutter again for viewing.

    So the answer is yes, the camera does have "mechanical" (ie
    moving-parts) shutter and diaphragm, even though they may be
    combined and operated electrically.

    --
    John Bean
    John Bean, Nov 19, 2005
    #16
  17. "Neil Harrington" <> writes:

    > "Måns Rullgård" <> wrote in message
    > news:...
    > [ . . . ]
    >>
    >> Depth of field at a given distance is determined by three parameters:

    >
    > Four or five, actually, depending on how you look at it.
    >
    >> focal length, aperture, and circle of confusion.

    >
    > Also final magnification and viewing distance (which might or might not be
    > regarded as the same thing). These are the things that most depth of field
    > calculations tend to ignore. If you add to that the fact that not everyone
    > has exactly the same visual acuity, you get still another variable.


    Those factors are included in the choice of circle of confusion.

    >> The first two are determined by the optics. The circle of
    >> confusion is a somewhat subjective property, and is a function of
    >> the required sharpness in the final image and the size of the
    >> recording medium. The image is perfectly focused only at one exact
    >> distance.

    >
    > And not even that, if "perfectly focused" is taken to mean that a
    > point on the subject is represented as a true point at the film
    > plane. That never happens, with any lens ever manufactured on this
    > planet. Because of lens aberrations, the "plane of best focus" may
    > well be slightly thicker than a true plane.


    Correct, and it might not even be a plane, but somewhat curved.


    [...]

    Quite so.

    --
    Måns Rullgård
    =?iso-8859-1?q?M=E5ns_Rullg=E5rd?=, Nov 19, 2005
    #17
  18. "Måns Rullgård" <> wrote in message
    news:...
    > "Neil Harrington" <> writes:
    >
    >> "Måns Rullgård" <> wrote in message
    >> news:...
    >> [ . . . ]
    >>>
    >>> Depth of field at a given distance is determined by three parameters:

    >>
    >> Four or five, actually, depending on how you look at it.
    >>
    >>> focal length, aperture, and circle of confusion.

    >>
    >> Also final magnification and viewing distance (which might or might not
    >> be
    >> regarded as the same thing). These are the things that most depth of
    >> field
    >> calculations tend to ignore. If you add to that the fact that not
    >> everyone
    >> has exactly the same visual acuity, you get still another variable.

    >
    > Those factors are included in the choice of circle of confusion.


    Well, "circle of confusion" is generally taken to mean "at the film plane."
    Obviously there's no way any depth of field scale or table can know ahead of
    time what the degree of final enlargement will be, or the viewing distance.
    Some assumptions have to be made, and those assumptions are likely to be
    very wrong. For example, an 11x14 print may be viewed while holding it in
    the hands, or while framed and hanging on a wall several feet away. The same
    depth of field calculation cannot apply to both.

    DoF scales on Japanese lenses for 35s generally use about .033 mm for the
    limiting circle of confusion, as I recall. German lenses for 35s on the
    other hand use a more generous CoC for the calculations, so German lenses
    will show a greater DoF than Japanese lenses at the same f-stop and
    distance, if the DoF scale is to be believed. Obviously there isn't really
    any difference between them; German lenses do not have some magical ability
    to extend depth of field. ;-)

    I have DoF tables that purport to show depth of field down to a fraction of
    an inch, which always struck me as somewhat hilarious. Minolta used to
    supply such tables with all their lenses. I have one of them in front of me
    now. It shows, for example, that the 85mm lens at f/16, focused at 8 feet,
    has a depth of field of 6' 10 7/16" to 9' 7 1/16". So in that circumstance
    the image would be sharp at nine feet, seven and one-sixteenth inches, but
    unsharp at nine feet, seven and one-eighth inches, if we are to believe the
    table. This sort of "precision" is about as useful as trying to measure
    Jell-O with a micrometer, but some people evidently take these tables
    seriously.


    >
    >>> The first two are determined by the optics. The circle of
    >>> confusion is a somewhat subjective property, and is a function of
    >>> the required sharpness in the final image and the size of the
    >>> recording medium. The image is perfectly focused only at one exact
    >>> distance.

    >>
    >> And not even that, if "perfectly focused" is taken to mean that a
    >> point on the subject is represented as a true point at the film
    >> plane. That never happens, with any lens ever manufactured on this
    >> planet. Because of lens aberrations, the "plane of best focus" may
    >> well be slightly thicker than a true plane.

    >
    > Correct, and it might not even be a plane, but somewhat curved.


    Yes, quite so.

    Neil
    Neil Harrington, Nov 19, 2005
    #18
  19. "Armando" <> wrote in message
    news:yJxff.2880$...
    > OP here.
    >
    > My camera is a Sony DSC-S50. A 2.1 MP beast from a few years back, but it
    > still impresses me now and then. It's my first and so far only digital
    > (not counting the not-really-serious 640x480 binocu-cam I got as a gift
    > recently).
    >
    > I never even thought about SLRs when I asked the question! Of course the
    > aperture is in the lens, of course there's a mechanical shutter. Duh on
    > me. So let me rephrase (or narrow the scope of) my question. In *MY*
    > camera, how do they do the "f-stop"? I select it from the GUI, and not by
    > spinning a ring on the lens. This is why it feels fake. I did actually
    > try a test once, I now recall, but I don't remember seeing much difference
    > with various settings.
    >
    > Thanks again,
    >
    > Armando


    I'm not at all familiar with Sonys, but on every digital camera I own there
    really are different *physical* f-stops. If the Exif information for the
    photo shows a certain f-number, I think you can be pretty confident that's
    what it was, within reasonable tolerances.

    That said, there almost certainly is not the same *range* of f-stops that
    you're used to with 35s, unless of course we're talking about a digital SLR.
    A few of my digital point-and-shoots only have two different apertures at
    any given focal length (as with most zooms, the aperture changes somewhat
    with changes in the focal length). And on such cameras, these two apertures
    are only two about stops apart, sometimes even less. If you have a typical
    compact camera it probably doesn't go down to a smaller aperture than f/8,
    and maybe not that small. Since even a large aperture has a lot more depth
    of field on such short-focal-length lenses than it would on a typical lens
    for a 35, and you don't any have really small apertures like f/16 or so, it
    is often hard to see much difference in depth of field with small digicams.

    Neil
    Neil Harrington, Nov 19, 2005
    #19
  20. "Neil Harrington" <> writes:

    >I have DoF tables that purport to show depth of field down to a fraction of
    >an inch, which always struck me as somewhat hilarious. Minolta used to
    >supply such tables with all their lenses. I have one of them in front of me
    >now. It shows, for example, that the 85mm lens at f/16, focused at 8 feet,
    >has a depth of field of 6' 10 7/16" to 9' 7 1/16".


    That's probably the result of someone in Japan translating DOF tables
    with distances in decimal metres into the incomprehensible (to them)
    system of feet, inches, and fractions of an inch.

    Dave
    Dave Martindale, Nov 19, 2005
    #20
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