comparing depth of field

Discussion in 'Digital Photography' started by bucky3, Jun 6, 2008.

  1. bucky3

    bucky3 Guest

    Is there an objective spec that can be used to compare depth of field
    for different cameras/lenses? Would hyperfocal distance be able to
    serve this purpose?

    I'm not an expert on photography. I would like to get a non-SLR camera
    that can produce good bokeh (shallow depth of field), but I would like
    to be able to compare specs.
     
    bucky3, Jun 6, 2008
    #1
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  2. On Jun 6, 4:57 am, bucky3 <> wrote:
    > Is there an objective spec that can be used to compare depth of field
    > for different cameras/lenses? Would hyperfocal distance be able to
    > serve this purpose?
    >
    > I'm not an expert on photography. I would like to get a non-SLR camera
    > that can produce good bokeh (shallow depth of field), but I would like
    > to be able to compare specs.


    Even the hyperfocal computation is not totally objective. All require
    a value for acceptable blur circle/coc. That value is still somewhat
    subjective.

    In order to control depth of field you need some degree of exposure
    control, like aperture priority and a very fast lens if you want a
    narrow depth of field. As long as you are shooting wide open, the
    format size and f/# of the lens pretty well control depth of field, so
    it shouldn't vary much from camera to camera with the same format
    size, focal length and f/#.
     
    Don Stauffer in Minnesota, Jun 6, 2008
    #2
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  3. bucky3

    ben brugman Guest

    "bucky3" <> schreef in bericht
    news:...
    > Is there an objective spec that can be used to compare depth of field
    > for different cameras/lenses? Would hyperfocal distance be able to
    > serve this purpose?
    >
    > I'm not an expert on photography. I would like to get a non-SLR camera
    > that can produce good bokeh (shallow depth of field), but I would like
    > to be able to compare specs.


    To compare depth of field, you need to determine how to compare.
    On way of doing is, is using a DOF calculator. And use a circle of
    not determined by the format, but fixed as compared to the diagonal.
    For example 1/1500 of the diagonal. This makes comparing of different
    formats with different aperature settings possible.

    But a ROUGH way is:
    If the size of a sensor is X times the size of another sensor the aperature
    number should be divided with the same number X.

    Examples:
    1 Sensor 1/6 in size of 35 mm format, aperature should be 1/6 of the number
    in 35 mm format. 35 mm f 4.0 would be in 1/6 sensor size f 0.666666

    Or the other way around 1/6 sensor size with 2.8 as largest aperature. Would
    be for 35 mm format 6 times 2.8 is f 16.8

    (The calculation is bases on the same angle of view, de same subject
    distance
    and the same coc where coc is a set fraction of the diagonal)

    ben

    (The rough method is not totaly accurate, but works for all subject
    distances and
    for all angles of view and is precise enough in all but the most critical
    situations).
     
    ben brugman, Jun 6, 2008
    #3
  4. bucky3

    bucky3 Guest

    On Jun 6, 7:08 am, Don Stauffer in Minnesota <>
    wrote:
    > Even the hyperfocal computation is not totally objective. All require
    > a value for acceptable blur circle/coc. That value is still somewhat
    > subjective.


    OK, but after you pick a value for acceptable COC, then the hyperfocal
    calculation would be an objective/consistent comparison?
     
    bucky3, Jun 6, 2008
    #4
  5. bucky3

    bucky3 Guest

    On Jun 6, 8:46 am, "ben brugman" <> wrote:
    > But a ROUGH way is:
    > If the size of a sensor is X times the size of another sensor the aperature
    > number should be divided with the same number X.
    > Or the other way around 1/6 sensor size with 2.8 as largest aperature. Would
    > be for 35 mm format 6 times 2.8 is f 16.8


    Thanks, that helps. I think it's helpful for me to think: "At f2.8, my
    puny point and shoot camera is only achieving the equivalent of f16.8
    with a full frame sensor."

    BTW, what is the value to use for sensor size? Is is the diagonal
    length? Area?
     
    bucky3, Jun 6, 2008
    #5
  6. bucky3

    Peter Irwin Guest

    bucky3 <> wrote:
    > On Jun 6, 7:08 am, Don Stauffer in Minnesota <>
    > wrote:
    >> Even the hyperfocal computation is not totally objective. All require
    >> a value for acceptable blur circle/coc. That value is still somewhat
    >> subjective.

    >
    > OK, but after you pick a value for acceptable COC, then the hyperfocal
    > calculation would be an objective/consistent comparison?


    If your CoC were chosen as a fraction of format diagonal,
    then it would be. One standard is diagonal/1720, which equals
    2 minutes of arc when viewed at the same distance as the diagonal
    of the format x enlargement.

    Peter.
    --
     
    Peter Irwin, Jun 6, 2008
    #6
  7. bucky3

    ben brugman Guest

    "bucky3" <> schreef in bericht
    news:...
    > On Jun 6, 8:46 am, "ben brugman" <> wrote:
    >> But a ROUGH way is:
    >> If the size of a sensor is X times the size of another sensor the
    >> aperature
    >> number should be divided with the same number X.
    >> Or the other way around 1/6 sensor size with 2.8 as largest aperature.
    >> Would
    >> be for 35 mm format 6 times 2.8 is f 16.8

    >
    > Thanks, that helps. I think it's helpful for me to think: "At f2.8, my
    > puny point and shoot camera is only achieving the equivalent of f16.8
    > with a full frame sensor."
    >
    > BTW, what is the value to use for sensor size? Is is the diagonal
    > length? Area?


    Because the sensorshapes are different the most practical way is to
    compare on diagonal. Most digital sensors are 3:4 where DSLR and
    35 mm camera's have 2:3. So you could compare the hight or the width
    of the sensor but diagonal is somewhere in the middle of both extremes.
    If the sensors have the same shape (both 2:3) it doesn't matter which size
    you take because then it works out the same.

    I like the 2:3 format better than the 3:4 format so for me I would preferre
    to
    compare the long side and clip away everything from the 3:4 format to make
    it the same.

    A way to estimate the chipsize is look at the focal length of the lens on
    the barrel
    at the wide end. (Often something between 4 and 10 mm). The 35 mm
    equivalent is often known. (Often 35, 36 or 38 mm). Divide those two
    numbers and you know how smal the chipsize is compared to 35 mm format.

    ben, who has a TZ3 which does support 2:3 format and actually has extra
    pixels
    in the width compared to the 3:4 format. Chipsize of the TZ3 is 1/6 of 35 mm
     
    ben brugman, Jun 6, 2008
    #7
  8. bucky3

    ben brugman Guest

    "Peter Irwin" <> schreef in bericht
    news:g2bt2s$o9h$...
    > bucky3 <> wrote:
    >> On Jun 6, 7:08 am, Don Stauffer in Minnesota <>
    >> wrote:
    >>> Even the hyperfocal computation is not totally objective. All require
    >>> a value for acceptable blur circle/coc. That value is still somewhat
    >>> subjective.

    >>
    >> OK, but after you pick a value for acceptable COC, then the hyperfocal
    >> calculation would be an objective/consistent comparison?

    >
    > If your CoC were chosen as a fraction of format diagonal,
    > then it would be. One standard is diagonal/1720, which equals
    > 2 minutes of arc when viewed at the same distance as the diagonal
    > of the format x enlargement.
    >


    hyperfocal calculation would be an objective/consisten comparison,
    but it's not very usefull, because it's difficult to interpret hyperfocal
    length. Comparing two hyperfocal length's does not realy illustrate the
    difference in DOF although it's consistent and objective.

    Go with the fraction of the format as written. (1/1720 of the diagonal
    is a high standard for DOF, most standards are less.) And compare DOFS
    with a DOF calculator. (And offcourse experiment with your camera's).

    Ben


    > Peter.
    > --
    >
    >
     
    ben brugman, Jun 6, 2008
    #8
  9. bucky3

    Archibald Guest

    On Fri, 6 Jun 2008 17:46:19 +0200, "ben brugman" <>
    wrote:

    >
    >"bucky3" <> schreef in bericht
    >news:...
    >> Is there an objective spec that can be used to compare depth of field
    >> for different cameras/lenses? Would hyperfocal distance be able to
    >> serve this purpose?
    >>
    >> I'm not an expert on photography. I would like to get a non-SLR camera
    >> that can produce good bokeh (shallow depth of field), but I would like
    >> to be able to compare specs.

    >
    >To compare depth of field, you need to determine how to compare.
    >On way of doing is, is using a DOF calculator. And use a circle of
    >not determined by the format, but fixed as compared to the diagonal.
    >For example 1/1500 of the diagonal. This makes comparing of different
    >formats with different aperature settings possible.
    >
    >But a ROUGH way is:
    >If the size of a sensor is X times the size of another sensor the aperature
    >number should be divided with the same number X.
    >
    >Examples:
    >1 Sensor 1/6 in size of 35 mm format, aperature should be 1/6 of the number
    >in 35 mm format. 35 mm f 4.0 would be in 1/6 sensor size f 0.666666
    >
    >Or the other way around 1/6 sensor size with 2.8 as largest aperature. Would
    >be for 35 mm format 6 times 2.8 is f 16.8
    >
    >(The calculation is bases on the same angle of view, de same subject
    >distance
    >and the same coc where coc is a set fraction of the diagonal)
    >
    >ben
    >
    >(The rough method is not totaly accurate, but works for all subject
    >distances and
    >for all angles of view and is precise enough in all but the most critical
    >situations).


    I agree with this approach... works surprisingly well for normal
    shooting situations.

    Note that focal length plays NO ROLE contrary to what many think,
    provided the framing of the image is the same.

    I also agree that rough methods are eminently useful for DOF
    calculations. That's all most of need to know. Furthermore, hardly
    anybody can actually compute accurate DOFs because the formulas depend
    on the exit pupil magnification, which usually is unknown.

    Archibald
     
    Archibald, Jun 6, 2008
    #9
  10. bucky3

    Peter Irwin Guest

    ben brugman <> wrote:
    >
    > hyperfocal calculation would be an objective/consisten comparison,
    > but it's not very usefull, because it's difficult to interpret hyperfocal
    > length. Comparing two hyperfocal length's does not realy illustrate the
    > difference in DOF although it's consistent and objective.


    Making a depth of field table based on hyperfocal distance is a piece
    of cake. Divide hyperfocal distance by the sequence 1, 2, 3, 4, ...

    So if the hyperfocal distance at f/2 of a certain lens is 100 feet,
    then make the table 100, 50, 33, 25, 20, 16.7, 14.3, 12.5, 11.1, 10, ...
    If you set the focus at 12.5 feet then everything from 11.1 feet
    to 14.3 feet will be in acceptable focus. You can make another table
    for f/2.8 by multiplying the hyperfocal distance by 0.707. For f/4
    you can just use the f/2 table but look two steps on each side so
    that at f/4 the depth of field at 12.5 feet will be from 10 to 16.7
    feet.

    > Go with the fraction of the format as written. (1/1720 of the diagonal
    > is a high standard for DOF, most standards are less.) And compare DOFS
    > with a DOF calculator. (And offcourse experiment with your camera's).
    >

    The trouble with a DoF calculator is that it hides the math so that
    people assume that the calculations are much more arcane than they
    actually are. Making your own DoF table will do much to take away
    the mystery.

    Peter.
    --
     
    Peter Irwin, Jun 7, 2008
    #10
  11. bucky3

    Bob Williams Guest

    bucky3 wrote:
    > Is there an objective spec that can be used to compare depth of field
    > for different cameras/lenses? Would hyperfocal distance be able to
    > serve this purpose?
    >
    > I'm not an expert on photography. I would like to get a non-SLR camera
    > that can produce good bokeh (shallow depth of field), but I would like
    > to be able to compare specs.



    Most small sensor P/S cameras give pretty deep DOF.
    I doubt that there would be significant differences between brands or
    models at the same aperture........BUT.......
    You can get a pretty convincing out of focus effect with Photoshop or
    third party digital "filters". The nice thing about, say Photoshop's
    Gaussian Blur Filter, is that you can very easily control the AMOUNT of
    "bokeh" that you apply to the image.
    Bob Williams
     
    Bob Williams, Jun 7, 2008
    #11
  12. bucky3

    ben brugman Guest


    > I agree with this approach... works surprisingly well for normal
    > shooting situations.
    >
    > Note that focal length plays NO ROLE contrary to what many think,
    > provided the framing of the image is the same.
    >


    Not that focal length plays a LARGE ROLE if the subject distance is
    near or beyond the hyperfocal distance. With modern small sensors
    the hyperfocal distance is close so the focal length plays a role in
    most day to day pictures.

    ben
     
    ben brugman, Jun 7, 2008
    #12
  13. On Jun 7, 6:09 am, "ben brugman" <> wrote:
    > > I agree with this approach... works surprisingly well for normal
    > > shooting situations.

    >
    > > Note that focal length plays NO ROLE contrary to what many think,
    > > provided the framing of the image is the same.

    >
    > Not that focal length plays a LARGE ROLE if the subject distance is
    > near or beyond the hyperfocal distance. With modern small sensors
    > the hyperfocal distance is close so the focal length plays a role in
    > most day to day pictures.
    >
    > ben


    Unless you are doing macro work.
     
    Don Stauffer in Minnesota, Jun 7, 2008
    #13
  14. bucky3

    Archibald Guest

    On Sat, 7 Jun 2008 13:09:59 +0200, "ben brugman" <>
    wrote:

    >
    >> I agree with this approach... works surprisingly well for normal
    >> shooting situations.
    >>
    >> Note that focal length plays NO ROLE contrary to what many think,
    >> provided the framing of the image is the same.
    >>

    >
    >Not that focal length plays a LARGE ROLE if the subject distance is
    >near or beyond the hyperfocal distance. With modern small sensors
    >the hyperfocal distance is close so the focal length plays a role in
    >most day to day pictures.
    >
    >ben


    Yes, this is true... but not much of an issue for most since the DOF
    is so great. Basically everything is in focus.

    Well, not everything. So if the near focus limit is critical for your
    picture, this needs to be taken into consideration. But I don't see
    many degrees of freedom here.... what if you are shooting a mountain
    scene but the log in the foreground is not sharp (out of the DOF
    zone). What would you do about it? Go to wide angle focal length?
    Don't you think that would change the composition?

    I think your only option is to stop down, if you want to keep your
    composition.

    Archibald
     
    Archibald, Jun 7, 2008
    #14
  15. bucky3

    ben brugman Guest

    "Don Stauffer in Minnesota" <> schreef in bericht
    news:...
    > On Jun 7, 6:09 am, "ben brugman" <> wrote:
    >> > I agree with this approach... works surprisingly well for normal
    >> > shooting situations.

    >>
    >> > Note that focal length plays NO ROLE contrary to what many think,
    >> > provided the framing of the image is the same.

    >>


    Not should be read as NOTE (sorry).
    >> Not that focal length plays a LARGE ROLE if the subject distance is
    >> near or beyond the hyperfocal distance. With modern small sensors
    >> the hyperfocal distance is close so the focal length plays a role in
    >> most day to day pictures.
    >>
    >> ben

    >



    > Unless you are doing macro work.

    This exception was allready there in the sentence: Note the part 'near or
    beyond', macro work normally is not near or beyond the hyperfocal distance
    but closer.

    ben
     
    ben brugman, Jun 8, 2008
    #15
  16. bucky3

    ben brugman Guest

    "Archibald" <> schreef in bericht
    news:...
    > On Sat, 7 Jun 2008 13:09:59 +0200, "ben brugman" <>
    > wrote:
    >
    >>
    >>> I agree with this approach... works surprisingly well for normal
    >>> shooting situations.
    >>>
    >>> Note that focal length plays NO ROLE contrary to what many think,
    >>> provided the framing of the image is the same.
    >>>

    >>
    >>Not that focal length plays a LARGE ROLE if the subject distance is
    >>near or beyond the hyperfocal distance. With modern small sensors
    >>the hyperfocal distance is close so the focal length plays a role in
    >>most day to day pictures.
    >>
    >>ben

    >
    > Yes, this is true... but not much of an issue for most since the DOF
    > is so great. Basically everything is in focus. \

    Well I think that is the issue everything being in focus.

    >
    > Well, not everything. So if the near focus limit is critical for your
    > picture, this needs to be taken into consideration. But I don't see
    > many degrees of freedom here.... what if you are shooting a mountain
    > scene but the log in the foreground is not sharp (out of the DOF
    > zone). What would you do about it? Go to wide angle focal length?
    > Don't you think that would change the composition?
    >
    > I think your only option is to stop down, if you want to keep your
    > composition.

    Go to a smaller format is an option as well.

    But I do agree with you that given a small sensor there is not a large
    degree of freedom for the DOF.

    ben
     
    ben brugman, Jun 8, 2008
    #16
  17. bucky3

    Paul Furman Guest

    Re: |GG| comparing depth of field

    bucky3 wrote:
    > Is there an objective spec that can be used to compare depth of field
    > for different cameras/lenses? Would hyperfocal distance be able to
    > serve this purpose?
    >
    > I'm not an expert on photography. I would like to get a non-SLR camera
    > that can produce good bokeh (shallow depth of field), but I would like
    > to be able to compare specs.


    The DOF calculators are a good idea. I wouldn't really try to boil it
    down to one number, it's really 3 numbers:
    -focal length (35mm equivalent is easier)
    -f/stop
    -sensor size

    If you want to have a soft background, use a longer focal length at the
    widest aperture, so a longer zoom will help with this.
    http://www.cambridgeincolour.com/tutorials/depth-of-field.htm


    --
    Paul Furman
    www.edgehill.net
    www.baynatives.com

    all google groups messages filtered due to spam
     
    Paul Furman, Jun 8, 2008
    #17
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