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Thread: The Wratten Mystery, or, What's My Factor?

  1. #11
    http://www.spiritsofsilver.com tgtaylor's Avatar
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    Re: The Wratten Mystery, or, What's My Factor?

    Quote Originally Posted by Doremus Scudder View Post
    But it's blue...

    Using the blue sky instead of a neutral source will almost certainly result in lower factors for blue filters (I know, not used that much) and higher factors for any filters that block blue (not that big of a deal, since you'd just end up overexposing a bit). Using something neutral gray would be more even across the board, which is why Kodak and others recommend doing that.

    But, if you're getting good results, what you're doing is close enough. Our medium has lots of wiggle room

    Doremus
    Doremus,

    Take your filters and meter outside and hold them up to the blue sky opposite the sun and see what you get. I did that this afternoon after my bike ride and this is what I got:

    Deep Yellow 15 (Tiffen glass filter): 15.4 EV sky, 13.6 EV sky and filter. (Tiffen 1-2/3/stops).
    Yellow Z001 (Cokin resin filter) 15.4 sky, 14.1 sky and filter (Cokin 1 stop).
    Green Z004 (Cokin resin filter): 15.4 sky, 13.4 sky and filter. (Cokin 2-stops).
    Blue Z020 (80A) (Cokin resin filter): 15.4 sky, 14.0 sky and filter. (Cokin 1-1/3 stops).
    Blue Z021 (80B) (Cokin resin filter): 15.4 sky, 14.3 sky and filter. (Cokin 1-stop).
    Red Z003 (Cokin resin filter): 15.4 sky, 11.4 sky and filter. (Cokin 3-stops). 1 stop off.
    Orange Z002 (Cokin resin filter): 15.4 sky, 12.8 sky and filter. (Cokin 1-1/3 stops). 2-2/3 stops off.
    Red Z007 (IR) (Cokin resin filter): 15.4 sky, 7.5 sky and filter. (Cokin ? - Amazon says 6 stops).
    Light yellow-warming (81B): 15.4 sky, 14.8 sky and filter. (Cokin 1/3 stop). 1/3 stop off.

    Sekonic L-758 DR light meter.

    Thomas

  2. #12

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    Re: The Wratten Mystery, or, What's My Factor?

    Ha!

    If you think I'm going to see any sun here in Eugene for a few weeks, you're an optimist. Much less a nice clear patch of blue sky opposite the sun. And then there are those pesky mountains and trees blocking the horizon too

    I don't know where you are, but "blue" sky here in the Willamette Valley is often closer to white than the blue skies in the mountains or down in the SW deserts. I guess your meter reading would depend greatly on the quality of the blue sky you're metering.

    Best,

    Doremus

  3. #13

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    Re: The Wratten Mystery, or, What's My Factor?

    Haha. I read Doremus' last comment... and was reminded of the old joke (popular among RIT students) that Kodak invented the 18% gray card because that was the color of the sky in Rochester. Having been born and raised in Rochester, and spent the first 55 years of my life there, I'll say there's at least a grain of truth in that.

  4. #14
    Drew Wiley
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    Re: The Wratten Mystery, or, What's My Factor?

    Tom - metering through filters doesn't work so well for two key reasons. First, the peak sensitivity of the meter is probably different from the film; second, pan films differ somewhat from one another in this respect, including in degree of blue sensitivity. To determine an accurate filter factor, one must make parallel gray card shots under identical conditions, with and without a filter, and then develop them together and read both on a densitometer afterwards. This is easier, or course, if a bracket test is done on roll film for the filtered version at slightly different settings, provided such a roll film has the same emulsion characteristics as the same label of sheet film. But this is such a light blue filter to begin with that it's not going to present a big problem.

  5. #15

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    Re: The Wratten Mystery, or, What's My Factor?

    [QUOTE= I'll say there's at least a grain of truth in that.[/QUOTE]

    A grain -- I get it.
    Philip Ulanowsky

    Sine scientia ars nihil est. (Without science/knowledge, art is nothing.)
    https://www.flickr.com/photos/156933346@N07/

  6. #16
    http://www.spiritsofsilver.com tgtaylor's Avatar
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    Re: The Wratten Mystery, or, What's My Factor?

    I'll stick with my method which, except for the orange filter, turned out pretty accurate with the Mfg's ratings. Once the rating is verified it is not necessary to do it again unless the condition of the filter changes. I think that they slight differences recorded were due to my trying to hand holding the filter flat against the meter is somewhat difficult due to the thinness of the resin filters and my innate reluctance to get fingerprints on it, and that I didn't have the meter pointed at the exact section of the sky with each reading. But then the value of the sky is consistent until the sun nears the horizon. Years and years ago I metered a composition thru the filter as Doremus suggested and ended-up with a bad exposure and never did that again.

    Instead of making"...parallel gray card shots under identical conditions, with and without a filter, and then develop them together and read both on a densitometer afterwards. This is easier, or course, if a bracket test is done on roll film..." I'll just stick with my method.

    Thomas

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