film speed

Discussion in 'B&W: Film, Paper, Chemistry' started by mitch brown, Nov 18, 2006.

  1. mitch brown

    mitch brown Subscriber

    Messages:
    236
    Joined:
    Apr 25, 2006
    Shooter:
    4x5 Format
    hi
    i just finnished my new film speed test using a slosh tray from PF for 6 4X5 sheets in PMK pyro. using my old system of yankee tank insert dunked in a 3qt container my fielm speed was iso 200 w hp5+. it now showes a iso of 800 is this strange.? most people have lower film speeds not higher.
    thanks
    mitch
     
  2. gainer

    gainer Subscriber

    Messages:
    3,725
    Joined:
    Sep 20, 2002
    Are you sure this is ISO? ISO determination requires a particular procedure. It will depend on contrast, which will depend on agitation and other factors.
     
  3. don sigl

    don sigl Member

    Messages:
    306
    Joined:
    Jul 6, 2006
    Location:
    Durham, NC
    Shooter:
    Multi Format
    This is probably too high for hp5. My speeds in PMK and Pyrocat are at 400. I'm not sure what process you are using to determine film speed. I shoot a grey card and expose at different speeds. Then process normally and read the exposures on a densitometer. The density that is about .1 above base+ fog determines film speed for the film/developer combination. You can then tweek development times to produce a ZV exposure (18% grey card) at about .65 + B+F density.
    This was the original approach AA used when establishing the Zone system. There are several variations, but the original method has always worked well for me.