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Re: Which filter for supressing yellow sodium light glow

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  • Ulhas Deshpande
    Thanks Nils I checked the filter set. My observations on the points made are below Ulhas ... yellowish ... emit a wide ... you can ... more ... I guess we have
    Message 1 of 13 , Oct 31 10:45 PM
      Thanks Nils
      I checked the filter set. My observations on the points made are
      below
      Ulhas
      --- In atm_free@yahoogroups.com, "Nils Olof Carlin"
      <nilsolof.carlin@...> wrote:
      >
      > The "classic" low-pressure sodium lights will look a dull orange-
      yellowish
      > light, and make you "color-blind" - the high-pressure type will
      emit a wide
      > spectrum (excepting precisely the sodium lines of the former) - if
      you can
      > distinguish colors in the light, it is this type - it will look
      more
      > "peach-colored".

      I guess we have the low pressure type lighting

      >
      > You don't mention if the filters are passband or stopband types -
      do they
      > transmit light only within a narrow band, or do they stop light
      only within
      > a narrow band of wavelengths? The graphs should tell.

      These filters are all passband types. The graphs show high
      transmission in the given band
      >
      > If the former, a filter for the sodium wavelengths will transmit
      essentially
      > only the light pollution from low pressure sodium lights, while
      cutting out
      > just about all starlight - hardly what you want.
      >
      > If you can find a "blue" filter that stops light from the sodium
      lines and
      > any redder light, it *may* be useful, since averted vision is
      distinctly
      > blue-green-sensitive.

      Thanks . I have two blue filters. One is 03FIV002 which has approx
      12 nm pass band centerd at 400 nm. The other is 03FIV004 with a
      transmission band of 12 nm centered at 450 nm.When I look thru these
      filters at a sunlit scene hardly anything is seen. Will that not dim
      the telescopic object too much?

      >
      > Nils Olof
      >
    • Nils Olof Carlin
      hello Ulhas, ... yellowish ... emit a wide ... you can ... more ... I guess we have the low pressure type lighting -So much the better - it is a bit more
      Message 2 of 13 , Nov 5, 2006
        hello Ulhas,



        > The "classic" low-pressure sodium lights will look a dull orange-
        yellowish
        > light, and make you "color-blind" - the high-pressure type will
        emit a wide
        > spectrum (excepting precisely the sodium lines of the former) - if
        you can
        > distinguish colors in the light, it is this type - it will look
        more
        > "peach-colored".

        I guess we have the low pressure type lighting

        -So much the better - it is a bit more economic to light, and also
        easier to avoid.


        These filters are all passband types. The graphs show high
        transmission in the given band

        Thanks . I have two blue filters. One is 03FIV002 which has approx
        12 nm pass band centerd at 400 nm. The other is 03FIV004 with a
        transmission band of 12 nm centered at 450 nm.When I look thru these
        filters at a sunlit scene hardly anything is seen. Will that not dim
        the telescopic object too much?

        Yes - I was not thinking of band-pass filters but "low-pass" cutting
        long-wavelength light and letting shorter-wavelength light pass - light
        of lower wavelength than 589 nm, the sodium D line.

        Narrow-band filters transmitting the OIII lines at 501 and 503 nm,
        sometimes including the H-beta
        line at 486 nm, are commonly used for nebulae, but I don't think the
        ones you write about are useful at all for astronomy. They were
        probably made for other purposes.

        Try look up
        http://en.wikipedia.org/wiki/Sodium_vapor_lamp

        maybe ordinary blue photo filters might help, at least you can see if
        you hold it up and look at a sodium lamp through it.

        regards, Nils Olof
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