film speed

[mitch brown]

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

 

[gainer]

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.

 

[don sigl]

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.