Focal length on digital

Discussion in 'Digital Photography' started by Rob, Oct 30, 2005.

  1. Rob

    Rob Guest

    I am just about to move from film to digital SLR (D100) and want to know if
    my lenses (24mm, 85mm, 80-200mm) will work at their same focal length as on
    my F90x. I use a digital compact and the focal lengths seem to be very
    different. A friend of mine said it was something to do the the sensor. I
    would appreciate if someone has a simple explanation for a very
    non-technical photographer!

    Rob
    Rob, Oct 30, 2005
    #1
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  2. "Rob" <> wrote in message
    news:dk35ed$3uv$...
    >I am just about to move from film to digital SLR (D100) and want to know if
    >my lenses (24mm, 85mm, 80-200mm) will work at their same focal length as on
    >my F90x. I use a digital compact and the focal lengths seem to be very
    >different. A friend of mine said it was something to do the the sensor. I
    >would appreciate if someone has a simple explanation for a very
    >non-technical photographer!
    >
    > Rob


    The lenses will be the same focal length. They just won't have the same
    field of view as you remember.

    Your lenses project a circular image at a set distance from the rear of the
    lens. You can see this by holding the lens between a light and a piece of
    paper. It projects this image onto your piece of film or digital sensor. The
    circle is designed to cover an area 36x24mm- i.e., a frame of 35mm film. The
    sensor in a digital camera is smaller than this. The effect is that the
    lens, when used on a digital body, gives a field of view approximate to that
    of one 1.5x the focal length on a 35mm body. The focal length, however, is
    unchanged- the depth of field remains the same at a given aperture, for
    example.

    As it is, then, a shorter focal length lens is needed if you want something
    that equates to a 24mm- effectively, a 16mm lens. A 16mm wideangle for a
    35mm camera would be rather heavier than your 24mm lens. Mercifully, a 16mm
    lens designed specifically for smaller format (digital) would not need to be
    as big as one designed for 35mm- probably no different in size or weight to
    a 24mm lens for 35mm. The practical problem is there is no fixed 16mm
    digital lens for Nikon. The closest you'd get is one of the zooms
    encompassing this range.

    Martin
    Martin Francis, Oct 30, 2005
    #2
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  3. Rob

    Monty Bonner Guest

    So if you want to sell lenses I might be interested, but I would keep them
    and just make the conversion.

    Girlfriend has N80 and I have D70s, we want a lens we can share like a
    70-200 or the 80-400, however on my camera, I will end up with 300 or 600 on
    my end, which is ok, but overkill, unless I am a couple of miles from my
    subject (joke). The 200 lenses is the superior because of the silent wave
    motor, but the rest is comparable.

    I still don't know how we will work this out, because one lens will suffice
    for both cameras, and one day I will hand off my D70s to her and get a
    better one, so hopefully the lenses will still carry over, so we don't have
    to purchase more.

    Later.

    Monty

    "Rob" <> wrote in message
    news:dk35ed$3uv$...
    >I am just about to move from film to digital SLR (D100) and want to know if
    >my lenses (24mm, 85mm, 80-200mm) will work at their same focal length as on
    >my F90x. I use a digital compact and the focal lengths seem to be very
    >different. A friend of mine said it was something to do the the sensor. I
    >would appreciate if someone has a simple explanation for a very
    >non-technical photographer!
    >
    > Rob
    >
    >
    Monty Bonner, Oct 30, 2005
    #3
  4. "Rob" <> writes:

    > I am just about to move from film to digital SLR (D100) and want to
    > know if my lenses (24mm, 85mm, 80-200mm) will work at their same
    > focal length as on my F90x. I use a digital compact and the focal
    > lengths seem to be very different. A friend of mine said it was
    > something to do the the sensor. I would appreciate if someone has a
    > simple explanation for a very non-technical photographer!


    Welcome to the mine-field! People get themselves and others confused
    all the time on this issue.

    The actual focal length of a lense is a matter of basic physics. It's
    fixed, it doesn't change.

    If you cut the center section out of a 35mm negative and enlarge just
    that part, you'll get a narrower angle of view than if you'd enlarged
    the entire negative. I'll *look* like you shot it with a longer focal
    length lens (although you may, depending on the degree of cropping,
    notice increased grain if you do this with film in the real world).

    Digital SLRs, except a couple of top-end models by Canon and a
    mid-level model by Kodak, have digital sensors smaller than a frame of
    35mm film. Consumer digicams have *much* smaller sensors than a frame
    of 35mm film.

    LOTS of people have spent enough time working with 35mm SLRs that they
    have a deeply-rooted idea of what angle of view they'll get with a
    lens of a given focal length *on a 35mm camera*.

    By the usual processes of cultural evolution (i.e. random thrashing
    around until something ugly that works much of the time is dominant),
    it's become standard for consumer P&S digicams to give the
    35mm-equivalent focal length for lenses. Since the different cameras
    have different sensor sizes, this is useful for comparing two of those
    cameras on an even basis, as well as for giving people familiar with
    35mm lenses an idea of what the field of view will be.

    People talk about the "focal-length multiplier" for digital SLRs --
    the Nikon models have a 1.5x multiplier, so your 50mm lens gives the
    same angle of view you'd get on a 35mm film camera with a 75mm lens.
    Some people will object strongly to the term "focal-length
    multiplier", and they're technically right, so to shut them up I often
    call it a "crop factor" instead.

    Why does it matter? Doesn't all *that* much. But when calculating
    depth of field, or bellows extension, you need to use the *real*
    physical focal length of the lens, not any of the other numbers that
    get thrown around. And many of us get hives when we see people
    misunderstanding things, even when the misunderstanding makes no
    difference to what most photographers do day-to-day. Call us anal if
    you like :).
    --
    David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    Dragaera/Steven Brust: <http://dragaera.info/>
    David Dyer-Bennet, Oct 30, 2005
    #4
  5. Rob wrote:
    > I am just about to move from film to digital SLR (D100) and want to know if
    > my lenses (24mm, 85mm, 80-200mm) will work at their same focal length as on
    > my F90x. I use a digital compact and the focal lengths seem to be very
    > different. A friend of mine said it was something to do the the sensor. I
    > would appreciate if someone has a simple explanation for a very
    > non-technical photographer!
    >
    > Rob


    Wouldn't you rather wait for the Nikon D200?

    - Siddhartha
    Siddhartha Jain, Oct 31, 2005
    #5
  6. Rob

    ASAAR Guest

    On 30 Oct 2005 15:19:54 -0600, David Dyer-Bennet wrote:

    > People talk about the "focal-length multiplier" for digital SLRs --
    > the Nikon models have a 1.5x multiplier, so your 50mm lens gives the
    > same angle of view you'd get on a 35mm film camera with a 75mm lens.
    > Some people will object strongly to the term "focal-length
    > multiplier", and they're technically right, so to shut them up I often
    > call it a "crop factor" instead.


    It only works sometimes. There have been a few here that almost
    belligerently insisted that terms such as "crop factor" were
    mistaken and shouldn't be used. (I disagreed)


    > And many of us get hives when we see people misunderstanding things,
    > even when the misunderstanding makes no difference to what most
    > photographers do day-to-day. Call us anal if you like :).


    Some of us can be anal. Others are real thing. :)
    ASAAR, Oct 31, 2005
    #6
  7. Rob

    Rob Guest

    Just read about this. I think I will wait. I'm sure in true Nikon style
    it'll be a bit a problem to get hold of to start with.

    Rob

    "Siddhartha Jain" <> wrote in message
    news:...
    >
    > Rob wrote:
    >> I am just about to move from film to digital SLR (D100) and want to know
    >> if
    >> my lenses (24mm, 85mm, 80-200mm) will work at their same focal length as
    >> on
    >> my F90x. I use a digital compact and the focal lengths seem to be very
    >> different. A friend of mine said it was something to do the the sensor.
    >> I
    >> would appreciate if someone has a simple explanation for a very
    >> non-technical photographer!
    >>
    >> Rob

    >
    > Wouldn't you rather wait for the Nikon D200?
    >
    > - Siddhartha
    >
    Rob, Oct 31, 2005
    #7
  8. Rob

    Rob Guest

    Thanks. I understand at last! Guess it's just a case of getting use to it.

    Rob



    "David Dyer-Bennet" <> wrote in message
    news:-b.net...
    > "Rob" <> writes:
    >
    >> I am just about to move from film to digital SLR (D100) and want to
    >> know if my lenses (24mm, 85mm, 80-200mm) will work at their same
    >> focal length as on my F90x. I use a digital compact and the focal
    >> lengths seem to be very different. A friend of mine said it was
    >> something to do the the sensor. I would appreciate if someone has a
    >> simple explanation for a very non-technical photographer!

    >
    > Welcome to the mine-field! People get themselves and others confused
    > all the time on this issue.
    >
    > The actual focal length of a lense is a matter of basic physics. It's
    > fixed, it doesn't change.
    >
    > If you cut the center section out of a 35mm negative and enlarge just
    > that part, you'll get a narrower angle of view than if you'd enlarged
    > the entire negative. I'll *look* like you shot it with a longer focal
    > length lens (although you may, depending on the degree of cropping,
    > notice increased grain if you do this with film in the real world).
    >
    > Digital SLRs, except a couple of top-end models by Canon and a
    > mid-level model by Kodak, have digital sensors smaller than a frame of
    > 35mm film. Consumer digicams have *much* smaller sensors than a frame
    > of 35mm film.
    >
    > LOTS of people have spent enough time working with 35mm SLRs that they
    > have a deeply-rooted idea of what angle of view they'll get with a
    > lens of a given focal length *on a 35mm camera*.
    >
    > By the usual processes of cultural evolution (i.e. random thrashing
    > around until something ugly that works much of the time is dominant),
    > it's become standard for consumer P&S digicams to give the
    > 35mm-equivalent focal length for lenses. Since the different cameras
    > have different sensor sizes, this is useful for comparing two of those
    > cameras on an even basis, as well as for giving people familiar with
    > 35mm lenses an idea of what the field of view will be.
    >
    > People talk about the "focal-length multiplier" for digital SLRs --
    > the Nikon models have a 1.5x multiplier, so your 50mm lens gives the
    > same angle of view you'd get on a 35mm film camera with a 75mm lens.
    > Some people will object strongly to the term "focal-length
    > multiplier", and they're technically right, so to shut them up I often
    > call it a "crop factor" instead.
    >
    > Why does it matter? Doesn't all *that* much. But when calculating
    > depth of field, or bellows extension, you need to use the *real*
    > physical focal length of the lens, not any of the other numbers that
    > get thrown around. And many of us get hives when we see people
    > misunderstanding things, even when the misunderstanding makes no
    > difference to what most photographers do day-to-day. Call us anal if
    > you like :).
    > --
    > David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    > RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    > Pics: <http://dd-b.lighthunters.net/>
    > <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    > Dragaera/Steven Brust: <http://dragaera.info/>
    Rob, Oct 31, 2005
    #8
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