Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,947   Posts: 1,557,848   Online: 849
      
Page 3 of 3 FirstFirst 123
Results 21 to 29 of 29
  1. #21

    Join Date
    Sep 2002
    Location
    Willamette Valley, Oregon
    Shooter
    Medium Format
    Posts
    3,684
    Quote Originally Posted by Helen B
    Is it normally the natural log or the base 10 log?
    I thought the latter - with one stop being 0.3, not 0.7?
    It's base 10. That base to the .3 power = 2, to the .6
    power = 4, to the .9 power = 8, and on, doubling the value
    with each additional .3.

    More often than not exposure is not in the log format. I also
    see EVs, ZONEs, and STOPs. I think 1, 2, 4 , 8, 16, 32, and on
    would also due.

    Perhaps the log format is used because of it's mathematical
    manipulativeness. Dan

  2. #22
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    The purpose of all this technicality is to get the scene brightness to register on the film so that proper development will produce a density range that fits the printing material. It's nice when it happens by plan instead of accident, but the possibility of accident is why we have different paper grades.
    Gadget Gainer

  3. #23
    Helen B's Avatar
    Join Date
    Jul 2004
    Location
    Hell's Kitchen, New York, USA
    Shooter
    Multi Format
    Posts
    1,557
    Images
    27
    "More often than not exposure is not in the log format. I also
    see EVs, ZONEs, and STOPs."


    If you think about it, they're logs too. Base 2.

    Best,
    Helen

  4. #24
    fhovie's Avatar
    Join Date
    Mar 2003
    Location
    Port Hueneme, California - USA
    Shooter
    Large Format
    Posts
    1,247
    Images
    92
    Quote Originally Posted by Helen B
    "More often than not exposure is not in the log format. I also
    see EVs, ZONEs, and STOPs."


    If you think about it, they're logs too. Base 2.

    Best,
    Helen
    That would be true for exposure but isn't tranmission density in base 10?

    I have received a sign from above - it appeared on my 361t - LAMP FAILURE!
    I guess that means I have to go shoot real pictures again .... (the new one is on order ... $80 from XRITE -ouch-)
    My photos are always without all that distracting color ...

  5. #25
    Helen B's Avatar
    Join Date
    Jul 2004
    Location
    Hell's Kitchen, New York, USA
    Shooter
    Multi Format
    Posts
    1,557
    Images
    27
    Frank,

    I thought that we'd already agreed that Log E and density were logs to base 10 - that was all sorted out on page 1. I was referring to EVs, zones and stops. They are all base 2 logs of relative exposure.

    Best,
    Helen

  6. #26

    Join Date
    Sep 2002
    Location
    Willamette Valley, Oregon
    Shooter
    Medium Format
    Posts
    3,684
    EVs and ZONEs most obviously. Dan

  7. #27

    Join Date
    Nov 2002
    Location
    Melbourne, Australia
    Shooter
    Medium Format
    Posts
    995
    Quote Originally Posted by fhovie
    How do you generate CI? if the SBR is 5 and the DR is 1.25 - what is the CI? and how do you get it - also - I know from my step wedge that my grade 2 paper can print a DR of 1.25 - What if I do a kalitype - I need a DR of 1.75? I am always reading about CI differences from AZO to Silver to Alt process. How do you calculate CI?
    The CI is the fraction DR/ER where the term ER is the Exposure Range as a log(base 10).

    In this example, the ER is 5 x 0.3 = 1.5. Each "stop" is an exposure difference of 0.3. Another way is to say the brightness range is 32 (2^5) and log(base 10) of 32 is 1.5 (actually 1.505 if you want to be unnecessarily fussy). DR is already in log(base 10) units.


    So CI = 1.25/1.5=0.83

  8. #28
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    As a matter of interest, sensitivity of human vision is pretty much logarithmic. The just noticeable difference between two brightnesses is a nearly constant ratio. There's a lot more to it than that, but it's a good approximation over the usual range of adaptation.
    Gadget Gainer

  9. #29
    fhovie's Avatar
    Join Date
    Mar 2003
    Location
    Port Hueneme, California - USA
    Shooter
    Large Format
    Posts
    1,247
    Images
    92
    Thanks John

    Quote Originally Posted by john_s
    The CI is the fraction DR/ER where the term ER is the Exposure Range as a log(base 10).

    In this example, the ER is 5 x 0.3 = 1.5. Each "stop" is an exposure difference of 0.3. Another way is to say the brightness range is 32 (2^5) and log(base 10) of 32 is 1.5 (actually 1.505 if you want to be unnecessarily fussy). DR is already in log(base 10) units.


    So CI = 1.25/1.5=0.83
    My photos are always without all that distracting color ...

Page 3 of 3 FirstFirst 123


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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