Magnification

Discussion in 'Digital Photography' started by mark.worthington, Mar 17, 2005.

  1. Hi,

    I was looking at this magpie on the lawn at 12X digital zoom on a
    38-114mm lens so that means that the effective focal length should have
    been around 450mm or 9x magnification. However when I looked through a
    pair of 10x50 binoculars, the bird looked much bigger with lots of
    detail and you could see the slight blue colour that magpies have on
    their wings. Would an optical zoom of 450mm given a comparable image to
    the binoculars?

    Thanks

    Mark
    mark.worthington, Mar 17, 2005
    #1
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  2. mark.worthington wrote:
    > Hi,
    >
    > I was looking at this magpie on the lawn at 12X digital zoom on a
    > 38-114mm lens so that means that the effective focal length should
    > have been around 450mm or 9x magnification. However when I looked
    > through a pair of 10x50 binoculars, the bird looked much bigger with
    > lots of detail and you could see the slight blue colour that magpies
    > have on their wings. Would an optical zoom of 450mm given a
    > comparable image to the binoculars?
    >
    > Thanks
    >
    > Mark


    First that 12X on the camera and the 10X on the binoculars is measuring
    something totally different.

    The 12X means the difference between the wide angle part of the lens and
    the telephoto end is 12 times.

    The binoculars mean that looking through them makes things look 10 times
    closer than not using them.

    There is not way of comparing the two.

    I might add that digital zoom is worthless. Only look at the optical
    zoom.

    --
    Joseph Meehan

    26 + 6 = 1 It's Irish Math
    Joseph Meehan, Mar 17, 2005
    #2
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  3. mark.worthington wrote:

    > Hi,
    >
    > I was looking at this magpie on the lawn at 12X digital zoom on a
    > 38-114mm lens so that means that the effective focal length should have
    > been around 450mm or 9x magnification. However when I looked through a
    > pair of 10x50 binoculars, the bird looked much bigger with lots of
    > detail and you could see the slight blue colour that magpies have on
    > their wings. Would an optical zoom of 450mm given a comparable image to
    > the binoculars?
    >
    > Thanks
    >
    > Mark
    >

    It is hard to make the comparison. With a photographic print, you are
    viewing what is called a 'real' image. When you view something in
    binoculars or a telescope, you are viewing a 'virtual' image. It
    appears to be a certain size. That size is measured in angle, however,
    not linear distance.

    The angle a print covers depends, of course, on how closely you view it.
    Of course, with a print you cannot focus on it if it is less than
    about 10 inches away. However, you can make the print many different
    sizes, and viewing different sized prints at 10 inches means the visual
    angle they cover varies also.
    Don Stauffer in Minneapolis, Mar 18, 2005
    #3
  4. mark.worthington

    Tumbleweed Guest

    "Don Stauffer in Minneapolis" <> wrote in message
    news:...
    > mark.worthington wrote:
    >
    >> Hi,
    >>
    >> I was looking at this magpie on the lawn at 12X digital zoom on a
    >> 38-114mm lens so that means that the effective focal length should have
    >> been around 450mm or 9x magnification. However when I looked through a
    >> pair of 10x50 binoculars, the bird looked much bigger with lots of
    >> detail and you could see the slight blue colour that magpies have on
    >> their wings. Would an optical zoom of 450mm given a comparable image to
    >> the binoculars?
    >>
    >> Thanks
    >>
    >> Mark
    >>

    In a word ... No!

    I use 12x50 'nocs and a 600mm long tom.
    The long tom theoretivally gives 12x "standard" but the image is much
    smaller than that delivered by the 'nocs.
    After cropping heavily I eventually end up with a comparable image - but
    that's hardly the same :eek:(
    Tumbleweed, Mar 18, 2005
    #4
  5. Tumbleweed <> wrote:

    : I use 12x50 'nocs and a 600mm long tom.
    : The long tom theoretivally gives 12x "standard" but the image is much
    : smaller than that delivered by the 'nocs.
    : After cropping heavily I eventually end up with a comparable image - but
    : that's hardly the same :eek:(

    The problem may be that the two devices are using different definitions
    for the same term. In Binoculars the multiplier is the apparent size of
    the object and will frequently also have a differerent field of view. The
    apparent image will appear wider to the eye since the eye can move and
    thus the virtual image at the eyepiece tends to be wider than a photo
    field of view. But with a photo, the multiplier is a ratio between the
    "normal" lens and the current lens (in mm). This was assumed to be about
    50mm in 35mm film cameras (tho this was slightly variable from camera to
    camera). But with Digital cameras the equivalent of this "normal" lens
    varies much more as each brand and model uses a different size of image
    collecting chip and thus the "normal" for your camera will be different
    from other cameras with a different sized chip, and very different from
    35mm film cameras. Thus the 600mm lens on a digital camera may be the
    equivalent of a 900mm lens on a film camera. This equivalency factor varys
    from brand to brand and model to model.

    Also the OP mentioned a difference in the "sheen" of the bird in question
    between the two devices. This may be somewhat due to differences in lens
    coatings. Some lenses are coated to reduce reflections within the unit
    which gets rid of those lines of bright circles that are frequently
    observed when a bright source is near an edge (or just off frame) of the
    image. This coating can also reduce some of the diffraction effects of
    bird feathers (which is what produces that color change of the feathers).
    This difference in the coatings can happen in many different items as the
    coatings are not standard to only one use. So you could have Binocs that
    don't see the sheen, and a camera that does, or vise verse.

    So in some ways, compairing the virtual image through binocs with what
    "should be" the same in a camera, it is like comparing apples and oranges.
    Similar in size, but just enough differences that the whole comparison
    goes awry. :)

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
    Randy Berbaum, Mar 19, 2005
    #5
  6. mark.worthington

    Tumbleweed Guest

    "Randy Berbaum" <> wrote in message
    news:d1gafu$l5p$...
    > The problem may be that the two devices are using different definitions
    > for the same term. In Binoculars the multiplier is the apparent size of
    > the object and will frequently also have a differerent field of view. The
    > apparent image will appear wider to the eye since the eye can move and
    > thus the virtual image at the eyepiece tends to be wider than a photo
    > field of view. But with a photo, the multiplier is a ratio between the
    > "normal" lens and the current lens (in mm). This was assumed to be about
    > 50mm in 35mm film cameras (tho this was slightly variable from camera to
    > camera). But with Digital cameras the equivalent of this "normal" lens
    > varies much more as each brand and model uses a different size of image
    > collecting chip and thus the "normal" for your camera will be different
    > from other cameras with a different sized chip, and very different from
    > 35mm film cameras. Thus the 600mm lens on a digital camera may be the
    > equivalent of a 900mm lens on a film camera. This equivalency factor varys
    > from brand to brand and model to model.
    >
    > Also the OP mentioned a difference in the "sheen" of the bird in question
    > between the two devices. This may be somewhat due to differences in lens
    > coatings. Some lenses are coated to reduce reflections within the unit
    > which gets rid of those lines of bright circles that are frequently
    > observed when a bright source is near an edge (or just off frame) of the
    > image. This coating can also reduce some of the diffraction effects of
    > bird feathers (which is what produces that color change of the feathers).
    > This difference in the coatings can happen in many different items as the
    > coatings are not standard to only one use. So you could have Binocs that
    > don't see the sheen, and a camera that does, or vise verse.
    >
    > So in some ways, compairing the virtual image through binocs with what
    > "should be" the same in a camera, it is like comparing apples and oranges.
    > Similar in size, but just enough differences that the whole comparison
    > goes awry. :)
    >
    > Randy


    That's an excellent reply Randy :eek:)
    Tumbleweed, Mar 19, 2005
    #6
  7. mark.worthington

    Tumbleweed Guest

    "Randy Berbaum" <> wrote in message
    news:d1gafu$l5p$...
    > Tumbleweed <> wrote:
    >

    <snip>
    > Also the OP mentioned a difference in the "sheen" of the bird in question
    > between the two devices.


    Just been mulling this over while I walked the dogs...

    The camera image is focused onto a ground glass (or plastic) screen at the
    same distance as the film plane.
    The binocular image is focused on the retina of the eye.
    I would expect the binocular image to be brighter and sharper to the eye.
    The image resolved on the film should be equally bright and sharp since it
    isn't degraded by the focusing screen.

    In the dim and distant past I remember having a number of interchangeable
    screens with my OM4. One of these was unground. It was designed for long
    lenses with small apertures to brighten the image.
    Brilliant for viewing but tricky for focusing if you needed D.O.F
    Tumbleweed, Mar 19, 2005
    #7
  8. Tumbleweed wrote:

    > "Don Stauffer in Minneapolis" <> wrote in message
    > news:...
    >
    >>mark.worthington wrote:
    >>
    >>
    >>>Hi,
    >>>
    >>>I was looking at this magpie on the lawn at 12X digital zoom on a
    >>>38-114mm lens so that means that the effective focal length should have
    >>>been around 450mm or 9x magnification. However when I looked through a
    >>>pair of 10x50 binoculars, the bird looked much bigger with lots of
    >>>detail and you could see the slight blue colour that magpies have on
    >>>their wings. Would an optical zoom of 450mm given a comparable image to
    >>>the binoculars?
    >>>
    >>>Thanks
    >>>
    >>>Mark
    >>>

    >
    > In a word ... No!
    >
    > I use 12x50 'nocs and a 600mm long tom.
    > The long tom theoretivally gives 12x "standard" but the image is much
    > smaller than that delivered by the 'nocs.
    > After cropping heavily I eventually end up with a comparable image - but
    > that's hardly the same :eek:(
    >
    >

    Okay, how many inches IS the image in your binoculars?
    Don Stauffer in Minneapolis, Mar 19, 2005
    #8
  9. mark.worthington

    Tumbleweed Guest

    "Don Stauffer in Minneapolis" <> wrote in message
    news:...
    >> I use 12x50 'nocs and a 600mm long tom.
    >> The long tom theoretivally gives 12x "standard" but the image is much
    >> smaller than that delivered by the 'nocs.
    >> After cropping heavily I eventually end up with a comparable image - but
    >> that's hardly the same :eek:(

    > Okay, how many inches IS the image in your binoculars?


    Oh no! You're not going to start that thread again are you?
    How many inches is your print?
    Is it twelve feet away on the wall?
    Is it two centimetres away in front of one eye?
    Which is the bigger image - a ten inch print four feet away or a 1/4 inch
    print in front of your nose?
    Tumbleweed, Mar 19, 2005
    #9
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