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  1. #41

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    The B+W Filter handbook (7 MB) lists the transmission diagrams of their filters. On page 61, 3rd row, 2nd column you'll find the yellow and orange filters. The Wratten 12 (minus blue), which bottoms out at 500 nm seems to fall in between the B+W 022 and 023. The roll-off area seems to be about 50nm for both the B+W as the Wratten 12 filter. There doesn't seem to be much mystery about it all. They're all just optical low-pass filters.

  2. #42

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    Quote Originally Posted by spijker View Post
    The B+W Filter handbook (7 MB) lists the transmission diagrams of their filters. On page 61, 3rd row, 2nd column you'll find the yellow and orange filters. The Wratten 12 (minus blue), which bottoms out at 500 nm seems to fall in between the B+W 022 and 023. The roll-off area seems to be about 50nm for both the B+W as the Wratten 12 filter. There doesn't seem to be much mystery about it all. They're all just optical low-pass filters.
    Hi there,

    You are quite correct that the B+W filters 22 and 23 are simple optical low pass filters. What you seem to be missing is that the Wratten 12 (Minus Blue) has both a low pass element where the straight line straddles across 500 nanometers PLUS a highly complex curve that delivers a variable response across the 300 - 343 nanometer spectrum (which is outside of what the typical human eye can respond to: i.e. wavelengths from about 390 to 700 nanometers) but one that film does respond to. You can view the curve here: http://motion.kodak.com/motion/uploa...ters/W2-12.pdf

    However, as stated earlier, the best way to assess the effect of filters is by doing practical tests which, I am sure you will find, demonstrates that the Wratten 12 is indeed a very special filter in terms of the relationship between effect and filter factor.

    Bests,

    David
    www.dsallen.de
    D.S. Allen, fotograf.

    Neue 3D Ausstellung/New 3D exhibition: www.german-fine-arts.com/berlin.html
    Neue Fotos/New Photos: http://shop.german-fine-arts.com/d-s-allen.html
    Vita/CV: www.german-fine-arts.com/allen.php

  3. #43

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    I did notice that , but was unable to understand what the effect on film would be.
    That is the range of UVA-ish
    I searched a bit and found this
    http://www.uvcorder.com/pdf/Ultravio...m_App_Note.pdf
    which says this
    "Standard camera lenses can be used for UV imaging in the near-UV band (340-400nm), although their transmission rolls off below about 330nm. For shorter wavelengths of UV, the standard practice is to use a special lens made of UV-transmitting materials such as quartz and calcium fluorite. These lenses are very expensive and come in a limited range of focal lengths and f/numbers."
    Also solo UV exposure times are in the 2-15 minute time frame (http://www.plumeltd.com/artzone/zuvhe.htm) and so would have a small effect at typical shutter speeds.
    What effect are you seeing from the UV effect on your Wrattan 12 shots?
    Are UV reflectors brighter? What is the benefit seen from the passing of 300-343 wavelengths?
    thanks



    Quote Originally Posted by David Allen View Post
    Hi there,

    You are quite correct that the B+W filters 22 and 23 are simple optical low pass filters. What you seem to be missing is that the Wratten 12 (Minus Blue) has both a low pass element where the straight line straddles across 500 nanometers PLUS a highly complex curve that delivers a variable response across the 300 - 343 nanometer spectrum (which is outside of what the typical human eye can respond to: i.e. wavelengths from about 390 to 700 nanometers) but one that film does respond to. You can view the curve here: http://motion.kodak.com/motion/uploa...ters/W2-12.pdf

    However, as stated earlier, the best way to assess the effect of filters is by doing practical tests which, I am sure you will find, demonstrates that the Wratten 12 is indeed a very special filter in terms of the relationship between effect and filter factor.

    Bests,

    David
    www.dsallen.de
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

    Regards
    Bill

  4. #44

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    David, I had seen the dip in the UV region but disregarded it as it is not visible for the human eye. You are right that B&W films are sensitive for UV light. But that would mean that the UV transparency of the Wratten 12 contributes to less darkening of a blue sky. This document show the transmission diagram of the Wratten 12 on page 26 fig. 7 which is also what B+W lists so that's easier to compare than a density diagram. The UV transmission part only reaches about 4% (10^-1.35 density) which is still about 4.5 stops attenuation. The same document lists that many B&W films have a UV absorption overcoat and that typically 50x more exposure is needed for UV light compared to visible light (page 18-19). So I doubt that the UV density dip has a noticeable affect on the photograph.

    Your comment that the Wratten 12 "has a strong effect on skies and only has a nominal filter factor of +1." remains of course and that's why it is very useful filter for B&W photography. I have a B+W 040 (orange) with a filter factor of 2 stops. That also darkens greens a bit which I often find useful as well. But if one doesn't want the greens to be affected by the filter then the yellow filters B+W 022, 023 & Wratten 12 would be a better choice.

    I agree that testing the effect of the various filters is the best way to go about it.

  5. #45

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    Quote Originally Posted by cowanw View Post
    I did notice that , but was unable to understand what the effect on film would be.
    That is the range of UVA-ish
    I searched a bit and found this
    http://www.uvcorder.com/pdf/Ultravio...m_App_Note.pdf
    which says this
    "Standard camera lenses can be used for UV imaging in the near-UV band (340-400nm), although their transmission rolls off below about 330nm. For shorter wavelengths of UV, the standard practice is to use a special lens made of UV-transmitting materials such as quartz and calcium fluorite. These lenses are very expensive and come in a limited range of focal lengths and f/numbers."
    Also solo UV exposure times are in the 2-15 minute time frame (http://www.plumeltd.com/artzone/zuvhe.htm) and so would have a small effect at typical shutter speeds.
    What effect are you seeing from the UV effect on your Wrattan 12 shots?
    Are UV reflectors brighter? What is the benefit seen from the passing of 300-343 wavelengths?
    thanks
    I am no scientist, so am not really qualified to say what the specific effects of the various wavelengths are.

    However, in practice:

    1. If you use colour infra-red film, the Wratten 12 does the best job of removing blue light.
    2. If you want to do the three black and white negatives projected together to create a colour image (as per a previous post) party trick, this only really works convincingly with the Wratten 12 (and the corresponding minus Green and minus Red Wratten filters).
    3. If you compare the effect of a Wratten 12 filter on B&W film to any other visually similar yellow filter, you will see a far more pronounced effect from the Wratten 12 filter.



    Bests,

    David
    www.dsallen.de
    D.S. Allen, fotograf.

    Neue 3D Ausstellung/New 3D exhibition: www.german-fine-arts.com/berlin.html
    Neue Fotos/New Photos: http://shop.german-fine-arts.com/d-s-allen.html
    Vita/CV: www.german-fine-arts.com/allen.php

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