Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,860   Posts: 1,583,140   Online: 870
      
Results 1 to 5 of 5
  1. #1

    Join Date
    Jul 2010
    Shooter
    35mm
    Posts
    144
    Images
    21

    A question about characteristic curve

    Dear All,

    I'm looking at different film's characteristic curves and I don't understand what exactly does 0 stand for on the X axis.

    For example, bw400cn http://www.kodak.com/global/en/profe...4036/f4036.pdf has 0 quite on the right side, only 3 f-stops from the shoulder.

    Is 0 set at the point where 18% gray at film's ISO is? Or is this point arbitrary?

    Thanks

  2. #2
    keithwms's Avatar
    Join Date
    Oct 2006
    Location
    Charlottesville, Virginia
    Shooter
    Multi Format
    Posts
    6,079
    Blog Entries
    20
    Images
    129
    log (1) =0, so the zero corresponds to 1 lux-second exposure.
    "Only dead fish follow the stream"

    [APUG Portfolio] [APUG Blog] [Website]

  3. #3

    Join Date
    Jul 2010
    Shooter
    35mm
    Posts
    144
    Images
    21
    Ah, ok... so that's log exposure in lux-seconds at film plane, right? How do I translate 1 lux second to anything more familiar? Is there a rule of thumb, eg: a gray card under bright sun, f5.6, 1/100, ISO 100 is approximately 1 lux second on film plane?

  4. #4
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,384
    Negative characteristics are used quite often in sensitometry. Note that in this book the unit for exposure is millilux-seconds. The former standard unit was lux-seconds. Five hundred millilux-seconds equals 0.5 lux-seconds. The log of 500 millilux-seconds is 2.7 but the log of 0.5 lux-seconds is a negative number (-1.7). All characteristic curves that used lux-seconds as the unit for exposure use negative characteristics.
    Be prepared for this when looking at most characteristic curves because the change to using millilux-seconds is fairly recent and most published curves use lux-seconds as the unit for exposure. Page 17
    Required reading http://motion.kodak.com/motion/uploa...y_workbook.pdf

  5. #5
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,221
    Quote Originally Posted by jernejk View Post
    Ah, ok... so that's log exposure in lux-seconds at film plane, right? How do I translate 1 lux second to anything more familiar? Is there a rule of thumb, eg: a gray card under bright sun, f5.6, 1/100, ISO 100 is approximately 1 lux second on film plane?
    I've uploaded an attachment that might help. The equation for Hg (exposure at the metered exposure point) is 8 meter candles * shutter speed or 8/ISO. B&W film speed is calculated using 0.80/Hm which falls 10x or 1.0 logs below Hg. 0.80/ISO will give you the exposure at the speed point. Example, for a 125 speed film Hg = 0.064 mcs and at the speed point it would measure 0.0064 mcs. 18% gray falls 1/2 stop above the metered exposure point. The exposure at the film plane for 18% gray with a 125 speed film would be half again 0.064 or 0.096 mcs.

    I have a digital copy of the paper, "Calibration Levels of Film and Exposure Devices" which I'll email if you're interested in delving deeper into the topic.
    Attached Thumbnails Attached Thumbnails Sunny 16.jpg  
    Last edited by Stephen Benskin; 09-20-2010 at 08:28 PM. Click to view previous post history.



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin