Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,208   Posts: 1,531,910   Online: 1142
      
Page 1 of 3 123 LastLast
Results 1 to 10 of 29
  1. #1
    fhovie's Avatar
    Join Date
    Mar 2003
    Location
    Port Hueneme, California - USA
    Shooter
    Large Format
    Posts
    1,247
    Images
    92

    Alphabet Soup? Help

    Could someone please explain the meaning of all those abreviations used in sensitometry ... CI etc. How are these generated? I can guess Dmax, Dmin B+F etc but many terms are used that still confuse me. Gamma?? etc
    My photos are always without all that distracting color ...

  2. #2
    Jeremy's Avatar
    Join Date
    Oct 2002
    Location
    Denton, TX
    Shooter
    Multi Format
    Posts
    2,767
    Images
    56
    CI = contrast index

    That is what I have always thought it meant, but I'm not sure so this is a good question!
    Let's see what I've got in the magic trash can for Mateo!

    blog
    website

  3. #3

    Join Date
    Sep 2002
    Shooter
    Large Format
    Posts
    4,530
    SBR = Subject Brightness Range.
    DR = Density Range
    ES = Exposure scale of the paper.
    Gamma = Method used by Ilford to define the two necessary points to claculate the slope of the straigh part of a H&D curve. Similar to CI which is what Kodak uses.
    Log E = Natural logarithm of the exposure. If we expose in units of light which double then the progression is 1, 2 , 4 , 8, 16, 32, 64, 128, 256. It is simpler to write the log than the numbers.
    Lux= Unit of light measurement, I leave it up to you to see your physics book..

    These are all I can recall off the top of my head, let me know if you need more definitions and which are they.

  4. #4
    Helen B's Avatar
    Join Date
    Jul 2004
    Location
    Hell's Kitchen, New York, USA
    Shooter
    Multi Format
    Posts
    1,557
    Images
    27
    "Log E = Natural logarithm of the exposure."

    Is it normally the natural log or the base 10 log? I thought the latter - with one stop being 0.3, not 0.7?

    Thanks,
    Helen

  5. #5

    Join Date
    Sep 2002
    Shooter
    Large Format
    Posts
    4,530
    Quote Originally Posted by Helen B
    "Log E = Natural logarithm of the exposure."

    Is it normally the natural log or the base 10 log? I thought the latter - with one stop being 0.3, not 0.7?

    Thanks,
    Helen
    You know Helen I dont recall exactly, I remember many years ago sitting with a calculator and workig out the numbers, so it might be base 10. In any case it is simple to figure it out...no?

  6. #6

    Join Date
    Dec 2004
    Location
    Milwaukee, Wi
    Shooter
    35mm
    Posts
    3,242
    dmin least density
    dmax maximum density
    bf base density + fog for a particularl amount of development
    fb+f as above
    SP speed point, the amount of exposure to xreate minimum density

  7. #7
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    It is the common log, base 10, that is used. Gamma was not first used by Ilford. It was employed many years ago by Hurter and Driffield and other research scientists to represent the slope of the straight line portion of the characteristic curve. If you only used that portion, gamma and CI would be the same value. Some films have practically no straight line. In any case, we use more of the curve than was thought proper in H&D days.
    Gadget Gainer

  8. #8
    Helen B's Avatar
    Join Date
    Jul 2004
    Location
    Hell's Kitchen, New York, USA
    Shooter
    Multi Format
    Posts
    1,557
    Images
    27
    The base 10 log is used for both the density and the exposure, with 0.3 being one stop. I wrote my previous post as a question because that seemed more conversational than a blunt contradiction. To be honest I find these internet discussions very difficult style-wise - I feel that I write in an overly harsh manner.

    Best,
    Helen

  9. #9
    fhovie's Avatar
    Join Date
    Mar 2003
    Location
    Port Hueneme, California - USA
    Shooter
    Large Format
    Posts
    1,247
    Images
    92
    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?
    My photos are always without all that distracting color ...

  10. #10

    Join Date
    Sep 2002
    Shooter
    Large Format
    Posts
    4,530
    Quote Originally Posted by Helen B
    The base 10 log is used for both the density and the exposure, with 0.3 being one stop. I wrote my previous post as a question because that seemed more conversational than a blunt contradiction. To be honest I find these internet discussions very difficult style-wise - I feel that I write in an overly harsh manner.

    Best,
    Helen
    No need to do so, anybody can make a mistake and it is no sin to correct it.

Page 1 of 3 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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