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Thread: Would a magenta filter work for increasing contrast...

  1. #11

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    Re: Would a magenta filter work for increasing contrast...

    Quote Originally Posted by Bob Salomon View Post
    One big problem you would face is finding an optical quality one.
    Bob, not exactly pure Magenta, but tending to it, FL-W filters are easily found multicoated from top manufacturers.

    The idea is using for BW a color correction filter for fluorescent lamps, to substantially darken green foliage in the background while keeping people's faces luminuous.

  2. #12

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    Re: Would a magenta filter work for increasing contrast...

    Quote Originally Posted by Pere Casals View Post
    Bob, not exactly pure Magenta, but tending to it, FL-W filters are easily found multicoated from top manufacturers.

    The idea is using for BW a color correction filter for fluorescent lamps, to substantially darken green foliage in the background while keeping people's faces luminuous.
    Each filter manufacturer made their fluorescent (FL S is a Tiffen trademark, they had sent us a cease and disest letter when we advertised B+Ws version) to what each manufacturer considered the average color of fluorescent tubes. That is why one brand might work in one location but not in another while a different brand would have completely different results.
    So just suggesting one is not a good answer.

    Since you seem to like numbers go research the color temperatures of the different tubes. Back in the day Minolta did publish a list that filled two columns on 8.5x11 paper!

  3. #13

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    Re: Would a magenta filter work for increasing contrast...

    Quote Originally Posted by Bob Salomon View Post
    each manufacturer considered the average color of fluorescent tubes.
    hmmm, this should be the reason why FL-W filters vary...

    In fact there are many flavours in fluorescent lamps, and for the same K we can have many possible SPDs ! Some tubes have horrible CRI...

  4. #14
    Steven Ruttenberg's Avatar
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    Re: Would a magenta filter work for increasing contrast...

    It sounds like there might be a use for using a magenta type filter for exposing the negative. Guess, the best way is to try it out and see how it works. 2 shots, 1 with, 1 without, maybe compare to a shot with a red, green and yellow filter as well. That would be fun.

  5. #15

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    Re: Would a magenta filter work for increasing contrast...

    Quote Originally Posted by Pere Casals View Post
    hmmm, this should be the reason why FL-W filters vary...

    In fact there are many flavours in fluorescent lamps, and for the same K we can have many possible SPDs ! Some tubes have horrible CRI...
    Color temps also vary with tubes.

  6. #16

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    Re: Would a magenta filter work for increasing contrast...

    Quote Originally Posted by Steven Ruttenberg View Post
    Guess, the best way is to try it out and see how it works.
    Just take a digital color image and use Photoshop to see the effects in the BW conversion, of course final result depends on light, film, filter and subject, but simulating it with Ps allows to understand the nature of the effect.


    Quote Originally Posted by Bob Salomon View Post
    Color temps also vary with tubes.
    Yes, of course, and this adds more troubles. Wedding photographers were scared by fluorescent lamps. I guess that today they are scared by bad LED lamps...

  7. #17

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    Re: Would a magenta filter work for increasing contrast...

    Quote Originally Posted by Pere Casals View Post
    hmmm, this should be the reason why FL-W filters vary...

    In fact there are many flavours in fluorescent lamps, and for the same K we can have many possible SPDs ! Some tubes have horrible CRI...
    K is noted as K. Not K!!

    From Wikipedia:

    Before the 13th CGPM in 19671968, the unit kelvin was called a "degree", the same as with the other temperature scales at the time. It was distinguished from the other scales with either the adjective suffix "Kelvin" ("degree Kelvin") or with "absolute" ("degree absolute") and its symbol was K. The latter term (degree absolute), which was the unit's official name from 1948 until 1954, was ambiguous since it could also be interpreted as referring to the Rankine scale. Before the 13th CGPM, the plural form was "degrees absolute". The 13th CGPM changed the unit name to simply "kelvin" (symbol: K).[11] The omission of "degree" indicates that it is not relative to an arbitrary reference point like the Celsius and Fahrenheit scales (although the Rankine scale continued to use "degree Rankine"), but rather an absolute unit of measure which can be manipulated algebraically (e.g. multiplied by two to indicate twice the amount of "mean energy" available among elementary degrees of freedom of the system).

  8. #18
    Steven Ruttenberg's Avatar
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    Re: Would a magenta filter work for increasing contrast...

    Quote Originally Posted by Bob Salomon View Post
    K is noted as K. Not K!!

    From Wikipedia:

    “Before the 13th CGPM in 1967–1968, the unit kelvin was called a "degree", the same as with the other temperature scales at the time. It was distinguished from the other scales with either the adjective suffix "Kelvin" ("degree Kelvin") or with "absolute" ("degree absolute") and its symbol was K. The latter term (degree absolute), which was the unit's official name from 1948 until 1954, was ambiguous since it could also be interpreted as referring to the Rankine scale. Before the 13th CGPM, the plural form was "degrees absolute". The 13th CGPM changed the unit name to simply "kelvin" (symbol: K).[11] The omission of "degree" indicates that it is not relative to an arbitrary reference point like the Celsius and Fahrenheit scales (although the Rankine scale continued to use "degree Rankine"), but rather an absolute unit of measure which can be manipulated algebraically (e.g. multiplied by two to indicate twice the amount of "mean energy" available among elementary degrees of freedom of the system).”
    I love science!

  9. #19

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    Re: Would a magenta filter work for increasing contrast...

    Quote Originally Posted by Bob Salomon View Post
    K is noted as K. Not K!!
    True, this was the 1960s notation ! thanks for the correction.

  10. #20
    Thalmees's Avatar
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    Re: Would a magenta filter work for increasing contrast...

    Quote Originally Posted by Steven Ruttenberg View Post
    I love science!
    That's really good.
    Photography as art, does not need very deep and specific knowledge.
    Science imply clever expectations based on basic but robust knowledge.
    Please read further.
    Quote Originally Posted by Steven Ruttenberg View Post
    It sounds like there might be a use for using a magenta type filter for exposing the negative. Guess, the best way is to try it out and see how it works. 2 shots, 1 with, 1 without, maybe compare to a shot with a red, green and yellow filter as well. That would be fun.
    So, what do you expect if you used two(2) light color filters stacked together?
    One is light Red, the other is light Blue.
    Do you think the Red part could darken greens like foliage?
    Then, the blue will lighten the sky?
    Something like the effect of pre-panchromatic films, may be 1800's century's plates.
    That's the Magenta as I think. It has Blue, built in!
    Please notice also that Pan chromatic films do not see like our eyes, and need a grade of Yellow(Y8-Y12) to see like human eyes. You are taking the film further away from our seeing nature if you use Magenta filter.
    Photographic contrast filters, from light Yellow(Y5 or Y8) to true Red(R25) plus green filters, has a cut point(actually it's a zone, not point) at which, most of the shorter wave lengths lights, are blocked almost completely. Its effect on film is expected very well.
    I could not imagine a similar curve for Magenta filter. Artistically, I do not feel well with the idea.
    But, for testing, studying, special situations or just for fun, every and any assumption can be considered worth of trying.

    The generosity of spirit in this forum is great, its warmly appreciated.
    ------------------------------

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