UV sensitivity of lens....explanation, please

Discussion in 'Digital Photography' started by Dale Bricker, Jan 6, 2005.

  1. Dale Bricker

    Dale Bricker Guest

    I have read that the lens of a certain older Olympus digital
    camera, the C-2020z, is "UV-sensitive", relatively speaking.
    I understand that this is intended to mean relative to other
    cameras with double-coated lenses, but I don't understand
    what the following numbers mean in the specifications for
    this particular cameram, as compared to other cameras:
    "6.5 - 19.5mm, F2.0 - 2.8.8 elements in 6 groups (equivalent
    to 35 -105 mm lens on 35mm camera)".

    For example, how does that compare to the following: "Helios
    58/2 has 6/4, Canon 28-80 has 10/10, and 75-300 has 13/9".

    For me, the more UV permeability of the lens, the better,
    as I want to attempt UV photography.

    Thanks for an explanation, or suggestion where to go online
    to find a good explanation.

    Dale Bricker
     
    Dale Bricker, Jan 6, 2005
    #1
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  2. Dale Bricker

    Jim Guest

    An element is an individual piece of glass. Sometimes elements are cemented
    together to form a group. In this case, the lens has 8 individual pieces of
    glass which are combined into 6 groups (i.e. some groups have only one
    element). The zoom lens itself has a focal length which can be set to any
    length between 6.7 mm and 19.5 mm. It has the same angles of view as a
    35-105 zoom has on a 35mm camera.
    Well, the Helios 58mm f2 lens has 6 elements in 4 groups, etc.
    None of these descriptions tell you much about the UV permeability.
    Jim
     
    Jim, Jan 6, 2005
    #2
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  3. Dale Bricker

    Bob Salomon Guest

    There are special filters made which appear to be opaque that transmit
    either only UV of a specified band width or only IR of a specified
    bandwidth.

    the UV versions would normally be used with long or short wave UV light
    sources.

    Is this what you want to do or are you looking to shoot items that and
    change color using a combination of normal and UV light?
     
    Bob Salomon, Jan 6, 2005
    #3
  4. Dale Bricker

    Dale Bricker Guest

    transmit >either only UV of a specified band width

    Yes, I bought a B+W 093 UV pass filter, but I wanted to know
    how to compare the UV sensitivity of my Oly C-2020's lens with
    the double-coated lenses of other cameras.

    Dale Bricker
     
    Dale Bricker, Jan 7, 2005
    #4
  5. Dale Bricker

    Peter Irwin Guest

    You might want to look at Robert Monaghan's page:
    <http://medfmt.8k.com/mf/uv.html>

    I think lens coating has very little to do with whether
    or not a lens passes UV. When Pentax announced their
    "Super Multi-Coated" lenses they pointed out that their
    new lenses incorporated UV filtering, but this doesn't
    seem to be inherent to multicoated lenses: some multicoated
    Nikkors appear to work quite well in the near-UV.

    UV photography with a digital camera has the special problem
    that most UV-pass filters (B+W 403, Tiffen 18A) also pass
    near-infrared and that the sensors on digital cameras tend
    to be more sensitive to the near-IR than the near-UV. You
    can tell if you are getting more UV effect or IR effect by
    taking a picture of white clouds against a blue sky: on
    a UV photograph the sky will be blank or with very little
    contrast between sky and clouds, the clouds may even
    be slightly darker than the very light sky. If you are getting
    mostly IR then the clouds will be light and the sky will
    be dark with much contrast between sky and clouds.

    That tells you a very little about the optical formula of
    the lens and is not useful for telling how well the lens
    will pass UV.

    Glass is an effective filter of the far-ultraviolet (anything
    shorter than arround 330nm. There are special and expensive
    lenses made of quartz and fluorite which will pass wavelengths
    much shorter than this. Regular B&W film (provided it does
    not incorporate a UV barrier layer) shows good sensitivity
    to UV as short as 230nm and some sensitivity to UV as short
    as 190nm: shorter wavelengths are stopped by the gelatine
    in the emulsion.

    Many modern lenses have built in UV filtering which cuts
    more of the near-UV than the inherent filtering of the
    glass. Both SMC Takumar/Pentax lenses, and Leitz/Leica
    lenses made after 1965 are claimed by their manufacturers
    to have fairly effective UV filtering built-in.

    Even if a lens passes near-UV there can be problems from
    some types of optical glass and some types of lens cement
    which can fluoresce under UV. The lens may also not
    be well corrected for UV, but this is often not a problem
    if the lens is stopped down a bit. One good thing about
    UV photography is that diffraction is much less of a
    problem: diffraction at f/22 with near-UV light is no
    worse than yellow/green light produces at f/16.

    EL-Nikkor enlarging lenses are claimed to be very well
    corrected for the 350-400 nm UV region as well as for
    visible light. So if you were looking for a lens for near-UV
    using an El-Nikkor on a bellows with a SLR could be
    a good idea. The 105mm or longer lenses should provide
    infinity focus with a bellows for a 35mm camera.
    You could just try a number of different lenses and
    see what works.

    Peter.
     
    Peter Irwin, Jan 7, 2005
    #5
  6. Dale Bricker

    stauffer Guest

    The lens is not the only problem. Silicon CCD chips are not nearly as
    sensitive to UV as film is, so you'd be better off using film. On the
    other hand, these chips ARE better at recording near-IR, though some
    cameras have filters to reduce the overall IR response.

    There are UV sensitive imaging chips made of materials other than
    silicon, but these are quite expensive for consumer use. They are used
    by military and astronomy folks.
     
    stauffer, Jan 7, 2005
    #6
  7. Dale Bricker

    Marvin Guest

    The capacity of a lens to pass UV light depends on the materials in the lens, which may be a glass or a plastic, or both in
    different lens elements. Camera makers usually block UV light, because it can create unwanted color effects.

    When Polaroid first made color film (actually, Kodak made it for them initially), it was tested on a prototype camera with
    glass lenses that didn't transmit UV light. When they put the film for the first time in a production Polaroid camera for
    color film, the colors were off because the plastic lens in the camera passed some UV. I don't remember whether they
    reformulated the film to work with the camera, or modified the lens to block UV.
     
    Marvin, Jan 7, 2005
    #7
  8. Dale Bricker

    KBob Guest

    If you are interested in UV photography you're best off with a DSLR so
    that specialized lenses can be used. Certain enlarging lenses are
    excellent for near-UV work, and can often be easily adapted to bellows
    units. I have found the Nikon D100 to be moderately sensitive to near
    UV, enough at least to shoot flowers and such under noonday sun, using
    a Rolyn U-360 pass filter. With a two-piece 58mm filter holder, these
    filters can be easily adapted to most cameras. For best results these
    filters usually need to be stacked with a hot mirror IR cut filter,
    since most UV pass filters also have a small response bump in the IR
    range that tends to spoil the effect. Have you checked out Bjorn
    Rorslett's page?
    http://www.naturfotograf.com/uvstart.html
    -kBob
     
    KBob, Jan 8, 2005
    #8
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