Adox CHS Art 100 reciprocity times

Discussion in 'B&W: Film, Paper, Chemistry' started by Jarvman, Oct 6, 2009.

  1. Jarvman

    Jarvman Member

    Messages:
    733
    Joined:
    Sep 9, 2006
    Location:
    Cardiff, Uni
    Shooter:
    Multi Format
    Can anybody point me to the reciprocity times for this film or should I just wing it using the times for FP4?
     
  2. AlanC

    AlanC Member

    Messages:
    335
    Joined:
    Feb 23, 2004
    Location:
    North Yorksh
    I have found that reciprocity failure definitely kicks in suddenly with this film. If I calculate that I need an exposure of 1 second, I give it 2 seconds or I know I will underexpose. But if a half second exposure is needed, giving it 1 second will overexpose it.

    Alan Clark
     
  3. Alessandro Serrao

    Alessandro Serrao Member

    Messages:
    997
    Joined:
    Oct 20, 2004
    Location:
    Rome, Italy
    Shooter:
    35mm
    It's quite absurd that even in 2009 some manufacturers don't publish data sheets!!
     
  4. Lee L

    Lee L Member

    Messages:
    3,247
    Joined:
    Nov 17, 2004
    Shooter:
    Multi Format
    Here's the unpublished data sheet, hidden on the Ilford web site on the FP4+ page link to the fact sheet:
    http://www.ilfordphoto.com/download.asp?n=474&f=2006216115141521.pdf

    The problem isn't that they don't publish tech info, it's that by all accounts from users who test it, the reciprocity information is outdated by a third of a century or more.

    Lee
     
  5. Markus Röhling

    Markus Röhling Member

    Messages:
    32
    Joined:
    Jan 27, 2009
    Location:
    Berlin
    Shooter:
    Large Format
    According to http://www.adox.de/ADOX_Filme/ADOX_CHS_Filme/ADOX_CHS_100/ADOX_CHS_100.html the CHS has a very low reciprocity failure:

    Markus
     
  6. Lee L

    Lee L Member

    Messages:
    3,247
    Joined:
    Nov 17, 2004
    Shooter:
    Multi Format
    Thanks for the link Markus. I'll throw in a table based on the information you linked to. I usually look at reciprocity data in two ways, the traditional Schwarzschild exponent used in Michael Covington's revised formula, and with another formula that seems to fit very well with a wide range of data from people doing careful reciprocity measurements.

    For this note and the attached chart, the variable x will be the time in seconds as metered, and the variable y will be the adjusted exposure time in seconds, which allows for the compounding effects of reciprocity failure when adjusting time rather than aperture.

    The Schwarzschild exponent from the Adox supplied data would be 0.90, used as the variable 'p' in the formula y=((x+1)^(1/p))-1

    The exponential equation I've found very useful is y=a*x^b+x Running a regression on the information found in Markus' link gives values of
    a = 0.18028451729247
    b = 1.2215054850993
    for Adox CHS100.

    The attached chart uses these equations to calculate new exposure times in seconds in the second and third columns based on the metered exposure time in seconds in the first column. The fourth column is the difference in the adjusted exposure times in stops, just as information on how the two methods diverge, which is only by 0.23 stops when adjusting from an initial exposure of 960 seconds.

    You can plug these formulae into your own spreadsheet and format it as you like.

    There will be batch-to-batch variations in reciprocity characteristics, and your particular usage will probably vary from these calculations, but they are a good starting point for finding your own results.

    Lee
     

    Attached Files: