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  1. #11
    ath
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    When comparing spectral sensitivity it is important how they were derived. There are at least two "standard" ways to plot the graphs. Based on the same data they look completely different.
    Compare the spectrae at page 3 for these two datasheets (german and english version of the same film, Ilford Delta 100): http://web.archive.org/web/199806101...00_Delta_G.pdf and http://web.archive.org/web/199806101.../100_Delta.pdf
    Regards,
    Andreas

  2. #12
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    Nice summary. Thank you for the effort.

    The Tri-X look is indeed due to the blue sensitivity mixed with its inherently low contrast, and I have heard that before. I call the TriX look a bit hazy, low in contrast, darker than normal skin tones, darker than normal plants...in short, slightly odd tonal relationships! I have always preferred HP5 for 35mm, and have recently switched in large format at well. I used to almost always filter Tri-X with a yellow-green filter...

    More detail would be nice, like being able to see the actual graphs instead of the writer's description. Raw information is much more educational to me than a running commentary trying to achieve the difficult task of explaining a graph that is not there.

    One thing irked me. I want to hear a more detailed explanation of why it is a fact that UV filters are necessary with the more UV-sensitive films...or was that just an opinion?
    Last edited by 2F/2F; 07-23-2008 at 03:43 PM. Click to view previous post history.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

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  3. #13

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    Opinion. It would also depend on where you are shooting, of course. Not so much here at sea level.

  4. #14

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    Quote Originally Posted by ath View Post
    When comparing spectral sensitivity it is important how they were derived. There are at least two "standard" ways to plot the graphs. Based on the same data they look completely different.
    Compare the spectrae at page 3 for these two datasheets (german and english version of the same film, Ilford Delta 100): http://web.archive.org/web/199806101...00_Delta_G.pdf and http://web.archive.org/web/199806101.../100_Delta.pdf
    Interesting. Other than I just stuck with English language data sheets, I don't know what to say. Why would Ilford use and publish two different methods?

  5. #15

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    Quote Originally Posted by Paul Verizzo View Post
    Another project from the depths of the lah-bor-a-tree on the bayou.
    Paul - I'm kind of disappointed - I was getting excited as I thought you had tested each of these films yourself, instead of collecting a bunch of links to somewhat related graphs of spectral sensitivity...

    I think your idea does hold some merit, but it looks like more work needs to be done to make a good comparison.

    Did you notice that not all the spectral graphs were made with the same color temp of light source? That could explain some of the "weird" behavior from the Foma. The Foma was tested at 2580K, while Fuji was at 5400K, Ilford was also at 2850K, and who knows what temp Kodak used - I can't see where they've stated it... Also, Foma did not show any scale on the y-axis. Perhaps they used a linear scale when the other 3 show that they are using a log scale. A linear scale would exaggerate small differences in response while the log scale would compress large differences.

    If you really want to take this to the next step (without going out and buying/making a recording spectrograph), you could get some software called Graphula (I think it is freeware) which lets you take a graph like you have from these companies, and then trace the plot on them, and it will generate a set of x,y data from it. Then, you can use info for blackbody radiation at 2850K and 5400K and then be able to convert the graphs that you've presented into graphs with the same color temp.

    Now that would be cool to see!

  6. #16
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    Quote Originally Posted by Paul Verizzo View Post
    Opinion. It would also depend on where you are shooting, of course. Not so much here at sea level.
    My point is that this is entirely up to the shooter, and how he or she wants the film to respond to UV. It can't be made as a definite blanket statement of fact.

    Something like, "in environmental circumstances in which it is desired to reduce blue sensitivity of Tri-X and other Kodak films, a UV filter can be employed. These situations might include..."
    Last edited by 2F/2F; 07-23-2008 at 03:44 PM. Click to view previous post history.
    2F/2F

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  7. #17

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    Thanks for some great observations!

    Quote Originally Posted by Kirk Keyes View Post
    Paul - I'm kind of disappointed - I was getting excited as I thought you had tested each of these films yourself, instead of collecting a bunch of links to somewhat related graphs of spectral sensitivity...

    I think your idea does hold some merit, but it looks like more work needs to be done to make a good comparison.

    Did you notice that not all the spectral graphs were made with the same color temp of light source? That could explain some of the "weird" behavior from the Foma. The Foma was tested at 2580K, while Fuji was at 5400K, Ilford was also at 2850K, and who knows what temp Kodak used - I can't see where they've stated it... Also, Foma did not show any scale on the y-axis. Perhaps they used a linear scale when the other 3 show that they are using a log scale. A linear scale would exaggerate small differences in response while the log scale would compress large differences.

    If you really want to take this to the next step (without going out and buying/making a recording spectrograph), you could get some software called Graphula (I think it is freeware) which lets you take a graph like you have from these companies, and then trace the plot on them, and it will generate a set of x,y data from it. Then, you can use info for blackbody radiation at 2850K and 5400K and then be able to convert the graphs that you've presented into graphs with the same color temp.

    Now that would be cool to see!
    Working backwards, no, I'm done. I did notice a few of the points you mention, and mentioned the lack of Foma X axis info.

    As to color temperature, I'm sort of scratching my head on that. How could you get strong UV/violet measurements from a 2800 K source? If you had some theoretical perfectly flat response film, you would still have a curve showing the light source, wouldn't you?

    And panchro films are really geared to daylight, some even having a different tungsten rating.

    I'd also like to hear more thoughts on the Foma curve shape. How intentional? Why?

  8. #18

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    Quote Originally Posted by Paul Verizzo View Post
    As to color temperature, I'm sort of scratching my head on that. How could you get strong UV/violet measurements from a 2800 K source? If you had some theoretical perfectly flat response film, you would still have a curve showing the light source, wouldn't you?
    Are you saying the Kodak data for Tri-X was made with a 2850K light source? How did you determine that? It does not say what color light source was used...

    I'm sure Fuji used 5400K since they make color film, I bet they use the same instrumentation to test their B&W films. Ilford, only makes B&W film, and 2850 is a fine temp for that, as long as you realize you it will show an increased response to red and a decreased response to blue (and little response to UV). Foma, again, B&W only, if I remember right. Kodak, perhaps, since they make color film, is using the same equipment to test B&W film as they use for color. That would mean they tested it at around 5400K or 5500K. That would give more blue and UV light in the test, which could be shown in the graph as a "greater" response to blue and UV.

    THat's why I suggested that the data needs to be converted to one color temp for all graphs (and one scale for all graphs too), otherwise they comparisons really can't be make at the level that you are trying to do. At least they can't be made with much accuracy...

    Foma curve shape is probably an artifact of the way the data was graphed combined with the 2850K light source.

    Theoretically flat response - at what color temp? You will get different responses at different temps. I guess shooting RAW in digital and then doing a color balance for individual lighting conditions will act as a flat spectral response. But I don't think you can make film to behave that way.

    Warm lighting will raise the red response, and cooler lighting will raise the blue response...

  9. #19
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    I am also interested to see the tests *all* done with daylight equivalent temp (somewhere in the 5000s, depending on location and season), photoflood equivalent temp (3200-3400K), and household lamp equivalent temp.

    I would imagine that if we were to contact the manufacturers asking what color temps light they used to determine the spectral sensitivity of their b/w films, they would tell us.
    2F/2F

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    - Rob Tyner (1944 - 1991)

  10. #20

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    As far as I can tell, everyone but Kodak listed the temp. Perhaps PE knows the practice there?

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