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  1. #21

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    I didn't say the green filter was passing UV and IR. I just said it could be. It is passing green, and presumably blocking the rest of the visible spectrum, but UV and IR aren't visible, so you'd never know by looking at it if it was blocking or transmitting those frequencies.

    From my experience, most visible light filters pass IR. They probably don't pass UV, but they could - you don't know unless you test it yourself or find a spec sheet on it. I've attached an image of B+W transmission curves. The 'green' filters are the 060 and 061. Notice how much IR they pass, especially the lighter green one. It looks like neither pass UV, at least as far as the graph it up to 300 nm. Presumably they don't pass much above that. Transmission of UV in the atmosphere stops around 200 nm.

    If you look through the B+W filter guide, they have numbers in square brackets after some of their names. For example, the B+W IR filter 092 has a [RG695] after it. That's the type of Schott glass used for the filter. You can look up the transmission curves somewhere on the Schott website - I found them once but couldn't find them just now. Or you can just look in the B+W transmission curve PDF.

    I also wanted to stress again that the 'native' sensitivity of film is UV/blue. That's why the alt processes use UV (UV photons have more energy than visible light, i.e. photoelectric effect) and why early films were ortho. The technology progression of film has been to extend sensitivity in the red direction. Digital sensors are the other way around. They all have hot mirrors to block IR, because they have huge sensitivity in the IR. I don't know what their UV sensitivity is. And also, just because the IR is below red, doesn't mean that the digital sensor is going to interpret IR as red - the green and blue channel filters could also transmit IR too. Same goes for UV on a digital camera - the RGB filters are designed for performance in visible light. The hot mirror takes care of the IR sensitivity and presumably the optics take care of the UV (most optics don't pass UV that well, and optical cements also filter UV).
    Attached Thumbnails Attached Thumbnails bwtrans.png  
    Last edited by Tim Gray; 03-22-2009 at 11:22 AM. Click to view previous post history.

  2. #22
    Contrastique's Avatar
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    Quote Originally Posted by cowanw View Post
    As to what the eyes see, I was kind of wondering which image most closely approximated the OP's actual eyeball view.
    Actually the first digital shot resembled what I saw with my own eyes best.
    The final shot when using the green filter "ate" some of the reddish light caused by the light on the floor aimed at the background which I expected anyway.
    Thank you for all the interesting comments in this thread. I realize I have to specialize a little in reading graphs (all kinds of graphs) as that knowledge does come in handy.

  3. #23
    Ole
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    There is a special gel filter which absorbs all UV, I have one from when I was photographing fluorescenct mineral many years ago. Even with colour film the UV light is very bright blue without a filter, with this filter everything except the fluorescence was totally black.
    -- Ole Tjugen, Luddite Elitist
    Norway

  4. #24
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    UV filters vs. black light filters

    Quote Originally Posted by Ole View Post
    There is a special gel filter which absorbs all UV, I have one from when I was photographing fluorescenct mineral many years ago. Even with colour film the UV light is very bright blue without a filter, with this filter everything except the fluorescence was totally black.
    I have a rockhound's fluorescent black light unit. It's got a very dark plastic filter over the tube. It's so dark that no visible light can be seen. But the UV gets through well enough to illuminate flourescent material within about eight inches from the bezel. I'd like very much to find a source for that black light filter.

    Something I discovered early on in my search for UV light sources and filters is that if you're interested in filters that pass UV, you need to use "black light" in your search instead of "ultraviolet" or "UV".
    "When the pin is pulled, Mr. Grenade is not our friend."
    - U.S. Marine Corps Grenade Training Manual

  5. #25
    Ole
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    Found it - it's a Wratten 2E. It's very pale yellow and cuts all UV light and a little of the shortest blue, but not enough to make a difference on photos. The UV is completely absorbed.
    -- Ole Tjugen, Luddite Elitist
    Norway

  6. #26
    EASmithV's Avatar
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    You must have a very patient model =D

    I love the effect you are going for though.
    www.EASmithV.com

    "The camera is an instrument that teaches people how to see without a camera."— Dorothea Lange
    http://www.flickr.com/easmithv/
    RIP Kodachrome

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