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Thread: Rollei RPX25 extended red sensitivity example

  1. #1

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    Rollei RPX25 extended red sensitivity example

    I'm in the process of developing sheets from this summer.
    I read that Rollei RPX25 had extended red sensitivity, but never thought more about it.
    But then I shot some subjects on my trip to the mountains on both RPX25 and Fomapan 400 or HP5+.
    And the difference is obvious.
    And interesting for the different creative options it opens up.

    So I thought I'd share.

    Click image for larger version. 

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    RPX25

    Click image for larger version. 

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    Fomapan400

    Same setup on my Chamonix 45H-1 with red filter. Both shoot with a few minutes in-between. Developed in Xtol 1+1.

  2. #2

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    Re: Rollei RPX25 extended red sensitivity example

    In this case, I prefer the Fomapan.

  3. #3

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    Re: Rollei RPX25 extended red sensitivity example

    This is interesting because at least per the respective specs, the difference is not huge, I mean, Foma starts rolling off at 680nm and Rpx at 700nm, both about as sharply.
    Of course by using a red filter you effectively amplify this because you're only letting red go through (I assume you mean a #25, which usually passes above ~580nm, of course the number depends on the brand, etc.). So if the incident light was spectrally uniformly distributed, then Rpx would get 20% more "light" in.

    It's just interesting how much difference there is in the trees. I am not an expert in spectrometry but I thought chlorophyll absorbs red light (creating a low right around the ~680 nm in fact), but probably it also depends on the type and state of vegetation...

    All this assumes that film linearity, development process and exposure have no significant say in the difference.

  4. #4

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    Re: Rollei RPX25 extended red sensitivity example

    Quote Originally Posted by Jim Noel View Post
    In this case, I prefer the Fomapan.
    Me too actually

  5. #5

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    Re: Rollei RPX25 extended red sensitivity example

    Quote Originally Posted by Kiwi7475 View Post
    This is interesting because at least per the respective specs, the difference is not huge, I mean, Foma starts rolling off at 680nm and Rpx at 700nm, both about as sharply.
    Of course by using a red filter you effectively amplify this because you're only letting red go through (I assume you mean a #25, which usually passes above ~580nm, of course the number depends on the brand, etc.). So if the incident light was spectrally uniformly distributed, then Rpx would get 20% more "light" in.

    It's just interesting how much difference there is in the trees. I am not an expert in spectrometry but I thought chlorophyll absorbs red light (creating a low right around the ~680 nm in fact), but probably it also depends on the type and state of vegetation...

    All this assumes that film linearity, development process and exposure have no significant say in the difference.
    Well, the Rpx rolls off from 700 to 750, and Foma from 680 to 690 so there is a definite difference (a bit uncertain in comparison since the scales are not equal). And as you say the red filter would only amplify this.
    I have another example that show the same thing. Sunny foliage with large difference i tone.

    I'm temped to try a few sheets with a R72 infrared filter. It should be possible to get an exposure at least.

  6. #6

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    Re: Rollei RPX25 extended red sensitivity example

    I prefer the Foma image, but it is good to have that extended red sensitivity option available.
    Thanks for doing the side-by-side test, that's the best way for a fair comparison.

  7. #7

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    Re: Rollei RPX25 extended red sensitivity example

    Quote Originally Posted by lassethomas View Post

    I'm temped to try a few sheets with a R72 infrared filter. It should be possible to get an exposure at least.
    Please post your results, that would be interesting & useful info!

  8. #8

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    Re: Rollei RPX25 extended red sensitivity example

    RPX25 is Agfa Aviphot 80, the same film as Retro 80s. An R72 filter will produce pretty good IR images.

  9. #9

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    Re: Rollei RPX25 extended red sensitivity example

    Quote Originally Posted by Dugan View Post
    Please post your results, that would be interesting & useful info!
    If I do, I will!.

    Have to remember on a really sunny day.

  10. #10

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    Re: Rollei RPX25 extended red sensitivity example

    Quote Originally Posted by lassethomas View Post
    If I do, I will!.

    Have to remember on a really sunny day.
    If youíre shooting with the Chamonix be mindful that at least a few years back their bellows were not IR proof.

    This may have changed or not, since then, I donít know.

    Just mentioning this is if you havenít shot IR with it before. There are solutions out there if you search, like covering with some specific dark cloths over the bellows, etc.

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