Paper Speed vs Film Speed

[Sam S]

Does anyone know what the correlation between ISO film speed and paper speed is? What I'm attempting to do is calibrate a film exposure meter so that it can read exposure times while exposing paper on my enlarger.

Sam S

 

[Thilo Schmid]

Sam,
They do not correlate at least not, if you do not also take into account the paper grade.
ISO Film Speed is defined as ISO = 0.8lxs / Hm, while Hm is the amount of light (in lxs) necessary for a density of 0.1logD above base.
ISO Paper Speed is defined as ISP-P = 1000lx / Hp, whereas Hp is the amount of light (in lxs) necessary to gain a paper density of 0.6logD.

I would recommend buying a lab meter.

 

[Sam S]

Thanks very much, Thilo.

Sam

 

[cesarb]

Sam,

Thilo is right, but it doesn't mean you can't use an exposure meter in the lab. Gossen, for instance, has a specific attachment for some models and after careful tests you may find equivalent ISO speed for any paper you select. Don't know about other makers, but wouldn't be surprise if one finds more options available.