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  1. #31
    Photo Engineer's Avatar
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    The red sensitivity of color papers is quite far into the red compared to camera films. It is made so due to the Tungsten balance of the paper and the need to match the dye set in C41 films. This imparts some IR sensitivity.

    Some automobile glasses are IR blockers. I bought a 5x5 square of it for cheap.

    It worked.

    PE

  2. #32
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    Quote Originally Posted by Photo Engineer View Post
    The red sensitivity of color papers is quite far into the red compared to camera films. It is made so due to the Tungsten balance of the paper and the need to match the dye set in C41 films. This imparts some IR sensitivity.

    Some automobile glasses are IR blockers. I bought a 5x5 square of it for cheap.

    It worked.

    PE
    Wouldn't any blue or bluish filter also block IR? Or does paper go that far into IR that normal filters can't touch it?
    Ask anyone who ever bought a Leica M8 if they've got a few spare IR/UV filters lying around...

    Also, depends what you call cheap, I'd say $75 for a 52mm is a bit pricey, but not outrageous.

    Meanwhile, if RA4 paper does go into far-IR, has anyone tried it with a 720nm filter to take IR photos?
    An awful lot of electrons were terribly inconvenienced in the making of this post.

  3. #33
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    Only the red layer is slightly NEAR IR sensitive. Not FAR IR sensitive! Automobile window glass scraps are cheap and filter IR. Also,, many modern window glass is IR blocking.

    Not all Blue glass is IR blocking though. It depends on bandpass.

    PE

  4. #34
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    Quote Originally Posted by Photo Engineer View Post
    Only the red layer is slightly NEAR IR sensitive. Not FAR IR sensitive! Automobile window glass scraps are cheap and filter IR. Also,, many modern window glass is IR blocking.

    Not all Blue glass is IR blocking though. It depends on bandpass.

    PE
    Damn, I thought I'd found a cheap way to make LF IR shots, it's always too good to be true though...
    And yeah, for some reason I keep thinking colour filters are just high-pass and low-pass, whereas you're right, they're probably more like bandpass.
    (I blame the audio engineer in me, where HP/LP filters are cheaper and easier to make, but that doens't really translate to light...)
    An awful lot of electrons were terribly inconvenienced in the making of this post.

  5. #35

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    What about exposing the paper 3 times, using red, green and blue tricolor filters? Giving the longest exposure through red (with IR-filter?), less through green filter and the least through blue filter (with UV-filter?) you could maybe balance the colors taking into account the sensitivities of the different layers and the temperature of the light. Not practical with portraits but maybe with still lifes.

  6. #36

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    Any suggestions as to what is wrong with the weird red colours here?

    If someone can tell me how to fix the colours in photoshop, I can apply the appropriate filtration...
    any thoughts?

  7. #37
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    A Wratten 70 filter has a good level of IR blocking so R/G/B is a good and bad idea. Good for IR blocking but bad for difficulty level. If you are up to it!

    As for the reds in the apples, I have no idea as I have no comparison. Single stimulus experiments are hard to comment on!

    PE

  8. #38
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    Mmm... Pomegranates... one of my weaknesses.
    Truzi

  9. #39

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    Quote Originally Posted by 73764 View Post
    What about exposing the paper 3 times...
    Interesting idea. I have a pretty good tripod and head, but I suspect registration might get messed up.
    I'm sure I'll try it this weekend! - Thanks!

  10. #40

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    How do I determine the CMY components of wratten filters? For instance what is an 85c or an 85b?

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