aperture and fixed zoom lens non DSLR

Discussion in 'Digital Cameras' started by Desert Dweller, Jul 18, 2007.

  1. I keep reading about apertures of F/22 for story-telling photos, showing
    foreground grass in focus as well as background mountains in focus. My
    shiny new non-DSLR digital camera I bought (Panasonic Lumix FZ8) only
    can close the aperture down to F/8. Does this mean I can't get those
    story-telling, landscape shots with my camera? Do I need a better
    camera? When I try to take those shots, the camera's auto-focus finds
    something to focus on and everything else is out of focus. If I choose
    manual focus, then whatever I do not focus on is still out of focus. How
    do I get everything in focus? And can F/8 do it? Is that the problem?

    In contrast, to get those macro shots of the subject popping out of the
    image so that everything else is totally out of focus, I've been seeing
    those images with apertures of F/1.4. My camera won't go that big, as
    its biggest setting is F/2.8. When I take the macro shots, the
    background is out of focus slightly, but not as much as the images I see
    in magazines, books, and on the web that claim to be at F/1.4. Do I
    need a better camera? Or is there more technique in getting those shots
    that I haven't learned?
    Desert Dweller, Jul 18, 2007
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  2. Desert Dweller

    Alex Monro Guest

    Compact non-interchangeable lens cameras such as the FZ8 have tiny
    sensors (IIRC yours is about 7mm diagonal), which gives vast depth of
    field - at f/8 and the wide end of the zoom you should be able to get
    everything from about half a metre away to infinity in focus if you
    focus at about 1 metre, the hypofocal distance.

    For a more detailed explaination of depth of field & hypofocal distance
    focussing, have a look here:


    If you want to use the online calculators, remember that the FZ8 has a
    1/2.5" sensor, which is slightly smaller than the 1/1.8" that some of
    the calculators go down to. Also, the focal length used is the actual
    focal length (6-72mm), not the 35mm equivalent (36-432mm).

    The pictures that you've been looking at were probably taken on 35mm,
    medium format (6x6cm etc.) or large format (up to 10x8") cameras, so
    they need much smaller apertures to get the depth of field.
    This is the opposite to the problem you described above, getting a
    narrow depth of field is difficult with a small sensor. However, to
    some extent you can sometimes improve things by zooming to a longer
    focal length and stepping back, since DoF is related to focal length.
    Alex Monro, Jul 18, 2007
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  3. [A complimentary Cc of this posting was sent to
    Alex Monro
    BS. Depth of focus is related ONLY to magnification and f-number.

    Hope this helps,
    Ilya Zakharevich, Jul 22, 2007
  4. [A complimentary Cc of this posting was NOT [per weedlist] sent to
    Good question. You forgot about wavelength; this is easy to do; I do
    not think I saw places where this is done 100% correct. So let's look
    through the math (I hope it is correct ;-).

    Magnification determines "depth magnification". f-number determines
    the angle of the cone of incoming light. E.g., if your 2 subjects are
    separated by 10cm depth-wise, their images near the focal plane will
    be separated by 10cm/M^2 depth-wise (here magnification is 1/M).
    Assuming the focal plane is in the middle, this would give 5cm/M^2
    off-focus distance.

    With f/8, this translates to 5cm/M^2/8 diameter of circle of confusion.

    Now return to depth of focus: we want the circle of confusion due to
    off-focus to be related to the circle of confusion of in-focus
    objects. The latter one is due to diffraction (depends only on
    f-number, and wavelength), and "lens quality". Since there is no
    other "reasonable" assumption - assume that the lens quality is the
    same (measured in the ratio of diameters of the actual circle of
    confusion to the circle of confusion of same-f-number
    diffraction-bound lens).

    So you get that magnification and f-number determine the depth of
    focus via the wavelength.

    Hope this helps,
    Ilya Zakharevich, Jul 22, 2007
  5. [A complimentary Cc of this posting was NOT [per weedlist] sent to
    In context of r.p.d, the wavelength is a fixed parameter. So without
    Nope. Diffraction is not "essentially geometrical".
    This argument of yours is complemente misplaced. Doubling the focal
    length and the object distance is NOT "enlarging everything by two";
    it is a much finer effect: e.g., note M *squared* in the initial
    argument, and that the size of the image does not change.
    Of course you can decide on discussing anything you like. However, I
    was discussing depth of focus.

    Hope this helps,
    Ilya Zakharevich, Jul 22, 2007
  6. Desert Dweller

    Alex Monro Guest

    Sorry, I missed the bit about macro, so obviously the close up rules

    Alex Monro, Jul 23, 2007
  7. [A complimentary Cc of this posting was sent to

    Why would somebody "wonder" about this?
    I do not think that your sentence makes any sense.

    Anyway, since "Depth of focus is related ONLY to magnification and
    f-number", you get the same DoF for 16mm film and 8x10in film - as far
    as you use the same magnification and f-number.

    I suspect that the reason why you are so confused is that TYPICAL
    MAGNIFICATIONS used with different sizes of film/sensors are very
    different; this is why typical f-numbers must be very different - if
    you want to achieve similar DoF. [The other, somewhat related, reason
    is the question of quality of lenses - for smaller formats it is
    easier to make lenses which are diffraction-bound at significant
    f-numbers; it looks like some recent 1/2.5in cameras have lenses which
    are diffraction-bound at f/4.]

    Hope this helps,
    Ilya Zakharevich, Jul 25, 2007
  8. BS. Depth of field is related to focal length and f:stop. Nobody asked
    about Depth-of-focus which is a different item.

    Small sensor cameras have a lot of Depth of field because they have
    short lenses. Common is 5-7mm at the short end. Even APS size sensor
    dSLR appear to have more DoF because users keep wanting to translate the
    crop factor into a magnification factor. They take a 1.5/1.6 factor and
    assume they are working with a longer lens. Then they comment, oh
    digital has more DoF than film.
    Not Disclosed, Aug 2, 2007
  9. [A complimentary Cc of this posting was sent to
    Not Disclosed
    Since depth of focus is related ONLY to magnification and f-number,
    the focal length comes into equation ONLY if a change in focal length
    changes the magnification.

    If you shoot the same subject with 50mm and 100mm lens with the same
    f-number, AND choose the distance so that the subject fills the frame
    both times, the depth of focus will be the same.
    This is very misleading. It is possible to make *exactly* the same
    shots with different form-factors of sensors (see my posts on the
    scaling laws, if you do not know the details). Just changing the
    format of the sensor would not change the depth of field - if you
    accompany it with appropriate changes in other parameters.

    "Small sensor cameras have a lot of Depth of field" makes sense ONLY
    in the following context:

    Given a 12mm sensor, to make an equivalent of a shot made at f/4
    with 25mm sensor, one needs to use f/2. The lens may not provide
    f/2 (or the aberrations at f/2 of a smaller lens may be more
    pronounced that at f/4 of a larger lens), so an equivalent shot
    could be not possible WITH THE GIVEN lens/sensor COMBINATION.

    Hope this helps,
    Ilya Zakharevich, Aug 2, 2007
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