neutal density filters for infrared

Discussion in 'Digital Photography' started by jpc, Jan 17, 2004.

  1. jpc

    jpc Guest

    Anyone have any info on neutal density filters for the infra red. I
    remember seeing a site a few years ago where someone meausured the
    transmittance of various brands and discovered there was some
    differences between them in the near infrared.

    thanks

    jpc
    jpc, Jan 17, 2004
    #1
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  2. jpc

    KenP Guest

    On Sat, 17 Jan 2004 12:45:39 -0600, jpc <> wrote:

    >Anyone have any info on neutal density filters for the infra red. I
    >remember seeing a site a few years ago where someone meausured the
    >transmittance of various brands and discovered there was some
    >differences between them in the near infrared.
    >
    >thanks
    >
    >jpc


    I've certainly never seen any application for ND filters for IR, quite
    the reverse, since you never seem to have enough sensitivity as it is,
    especially with newer cameras and their aggresive NIR filters.

    As to using an ND filter in place of IR filters, all I know is that
    sections of exposed film have been used for this. It is also likely
    that ordinary ND filters will have varying response to IR, since they
    are only intended to function in the visible spectrum.
    KenP, Jan 17, 2004
    #2
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  3. jpc wrote:

    > Anyone have any info on neutal density filters for the infra red. I
    > remember seeing a site a few years ago where someone meausured the
    > transmittance of various brands and discovered there was some
    > differences between them in the near infrared.


    I use a Hoya green filter lemme check ... I'll be right back ...
    a runofthemill Hoya deep green G (X1) filter with the IR-pass filter to
    more effectively control and attenuate IR. It turns out some ND filters
    are practically transparent even a little bit outside the visual
    spectrum. Can't blame them, that's not their job.

    Learned that little trick from Godfrey DiGiorgi, who hasn't posted here
    in a while. He had a demo image page showing the practical IR
    performance of several ND and color filters, which I confirmed.

    Corry

    --
    It Came From C. L. Smith's Unclaimed Mysteries.
    http://www.unclaimedmysteries.net
    Unclaimed Mysteries, Jan 18, 2004
    #3
  4. jpc

    jpc Guest

    On Sun, 18 Jan 2004 04:16:12 GMT, Unclaimed Mysteries
    <> wrote:

    >jpc wrote:
    >
    >> Anyone have any info on neutal density filters for the infra red. I
    >> remember seeing a site a few years ago where someone meausured the
    >> transmittance of various brands and discovered there was some
    >> differences between them in the near infrared.

    >
    >I use a Hoya green filter lemme check ... I'll be right back ...
    >a runofthemill Hoya deep green G (X1) filter with the IR-pass filter to
    >more effectively control and attenuate IR. It turns out some ND filters
    >are practically transparent even a little bit outside the visual
    >spectrum. Can't blame them, that's not their job.


    Thanks for the tip on the green filter. Hadn't thought about it but
    obviously if it is passing green it must be blocking red and a good
    part of the NIR.



    >
    >Learned that little trick from Godfrey DiGiorgi, who hasn't posted here
    >in a while. He had a demo image page showing the practical IR
    >performance of several ND and color filters, which I confirmed.
    >


    Did a Google search on DiGiorgi and found his site. The technical info
    on IR filters seems to be gone.

    Would you happen to remember which brands of ND filters block NIR?
    If the manufacture uses a broadband interference coating on the filter
    to block the visible I can see how the transmitance would increase for
    out of band radiation but if they used a absorbing coating-- a coating
    of nicrome for instance-- that should also block the NIR. My guess is
    that the cheaper ND filters have metallic coating but it would be nice
    to know for certain before I placed an order.

    jpc
    jpc, Jan 18, 2004
    #4
  5. jpc

    gr Guest

    <jpc> wrote
    >
    > Would you happen to remember which brands of ND filters block NIR?
    > If the manufacture uses a broadband interference coating on the filter
    > to block the visible I can see how the transmitance would increase for
    > out of band radiation but if they used a absorbing coating-- a coating
    > of nicrome for instance-- that should also block the NIR. My guess is
    > that the cheaper ND filters have metallic coating but it would be nice
    > to know for certain before I placed an order.


    What are you so concerned about? Digital camera IR sensitivity is about 7-11
    stops below that of visible light. Even if your ND filter was only partially
    effective against IR, you'd probably notice no IR until you were blocking 10
    stops or more of visible light.
    gr, Jan 19, 2004
    #5
  6. jpc

    jpc Guest

    On Sun, 18 Jan 2004 19:06:40 -0500, "gr"
    <> wrote:

    ><jpc> wrote
    >>
    >> Would you happen to remember which brands of ND filters block NIR?
    >> If the manufacture uses a broadband interference coating on the filter
    >> to block the visible I can see how the transmitance would increase for
    >> out of band radiation but if they used a absorbing coating-- a coating
    >> of nicrome for instance-- that should also block the NIR. My guess is
    >> that the cheaper ND filters have metallic coating but it would be nice
    >> to know for certain before I placed an order.

    >
    >What are you so concerned about? Digital camera IR sensitivity is about 7-11
    >stops below that of visible light. Even if your ND filter was only partially
    >effective against IR, you'd probably notice no IR until you were blocking 10
    >stops or more of visible light.


    I can remove the ir blocking filter on a low resoultion camera that I
    still use occasionally. With that out and an ir transmission filter
    over the lens I still overexpose the highlights in bright sunlight.
    And since I was planning to buy a few ND filters for another camera
    and project, why not buy filters that work on both cameras. Simple as
    that

    jpc
    >
    jpc, Jan 19, 2004
    #6
  7. jpc

    gr Guest

    <jpc> wrote
    >
    > I can remove the ir blocking filter on a low resoultion camera that I
    > still use occasionally.


    Interesting. Have you ever done that before? What's the process? (I may be
    interested in doing that myself.)
    gr, Jan 19, 2004
    #7
  8. jpc

    Chris Quinn Guest

    Have you tried http://www.wrotniak.net/photo/infrared/




    <jpc> wrote in message news:...
    > On Sun, 18 Jan 2004 04:16:12 GMT, Unclaimed Mysteries
    > <> wrote:
    >
    > >jpc wrote:
    > >
    > >> Anyone have any info on neutal density filters for the infra red. I
    > >> remember seeing a site a few years ago where someone meausured the
    > >> transmittance of various brands and discovered there was some
    > >> differences between them in the near infrared.

    > >
    > >I use a Hoya green filter lemme check ... I'll be right back ...
    > >a runofthemill Hoya deep green G (X1) filter with the IR-pass filter to
    > >more effectively control and attenuate IR. It turns out some ND filters
    > >are practically transparent even a little bit outside the visual
    > >spectrum. Can't blame them, that's not their job.

    >
    > Thanks for the tip on the green filter. Hadn't thought about it but
    > obviously if it is passing green it must be blocking red and a good
    > part of the NIR.
    >
    >
    >
    > >
    > >Learned that little trick from Godfrey DiGiorgi, who hasn't posted here
    > >in a while. He had a demo image page showing the practical IR
    > >performance of several ND and color filters, which I confirmed.
    > >

    >
    > Did a Google search on DiGiorgi and found his site. The technical info
    > on IR filters seems to be gone.
    >
    > Would you happen to remember which brands of ND filters block NIR?
    > If the manufacture uses a broadband interference coating on the filter
    > to block the visible I can see how the transmitance would increase for
    > out of band radiation but if they used a absorbing coating-- a coating
    > of nicrome for instance-- that should also block the NIR. My guess is
    > that the cheaper ND filters have metallic coating but it would be nice
    > to know for certain before I placed an order.
    >
    > jpc
    >
    >
    >
    >
    >
    >
    >
    >
    >
    >
    >
    >
    >
    >
    Chris Quinn, Jan 19, 2004
    #8
  9. jpc

    jpc Guest

    On Mon, 19 Jan 2004 07:43:48 -0500, "gr"
    <> wrote:

    ><jpc> wrote
    >>
    >> I can remove the ir blocking filter on a low resoultion camera that I
    >> still use occasionally.

    >
    >Interesting. Have you ever done that before? What's the process? (I may be
    >interested in doing that myself.)
    >


    The camera is a Sony where you can move the ir blocking filter in and
    out of the light beam. From what I can find out on the net because
    some brands of cloth are semitranlucent in the NIR Sony threw in some
    circuitry that causes the carmera to overexpose in daylight. This is
    a rather stupid fix since anyone who gets their kicks from this so
    called X-Ray effect can buy some very overpriced "x-ray filters" and
    it ruins the camera for creative NIR photography. Sint the "x-ray"
    filters are nothing more than your run of the mill NIR transmittance
    and ND filters I'm trying to gather up the technical info and buy my
    filters from a reputable source like B&H.

    Sony camera and perhaps some other brands--some Nikons I believe, have
    seperate IR blocking fillters. With most other cameras the blocking
    filter is laid down on the cover glass that protects the CCD or CMOS
    sensor so you are stuck with whatever IR leaks through the filter.

    If you are interested I'll post info on what I end up buying and how
    it works out.

    jpc
    jpc, Jan 19, 2004
    #9
  10. jpc

    jpc Guest

    jpc, Jan 19, 2004
    #10
  11. jpc

    gr Guest

    <jpc> wrote
    > On Mon, 19 Jan 2004 07:43:48 -0500, "gr"
    > <> wrote:
    >
    > ><jpc> wrote
    > >>
    > >> I can remove the ir blocking filter on a low resoultion camera that I
    > >> still use occasionally.

    > >
    > >Interesting. Have you ever done that before? What's the process? (I may

    be
    > >interested in doing that myself.)
    > >

    >
    > The camera is a Sony where you can move the ir blocking filter in and
    > out of the light beam.


    Oh, okay, I see. I thought you meant you were going to open up the camera
    and physically remove the blocking filter. That's what I am interested in
    doing. Now I understand you're just using the camera's own functionality.
    Thanks anyway.
    gr, Jan 19, 2004
    #11
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