Paper speed/contrast spec relationships

[dkonigs]

Okay, so I'm trying to figure out how to determine the amount of exposure required for a particular piece of printing paper, based entirely off of its published specifications.

The datasheets for any given paper tell me two relevant values... ISO(P) and ISO(R).
According to the ISO 6846:1992 spec, ISO(P) tells me how much exposure is required for a density of D=0.60. Meanwhile, the ISO(R) tells me the difference between the exposure for D=0.04 and D=0.90.

What I'm struggling to figure out, is the relationship between these exposure values. In other words, if I know the exposure to get D=0.60 and the ISO(R) contrast range, then how exactly do I determine the exposure for D=0.04? Is it even possible?

What sent me down this rabbit hole is trying to figure out how my RH Analyser Pro enlarging meter works, or how it could work if implemented differently. Its basically calibrated around the D=0.04 exposure and ISO(R) contrast range of a particular paper, and does all of its metering/calculations from there. As the actual exposure for D=0.04 isn't actually part of a paper's specifications, I'm trying to determine if I can somehow calculate it from the ISO(P) (D=0.60) exposure.

P.S. I'm really not looking for an experimental approach here. I want to be able to crunch all these numbers up-front, for the common/generic/standard/specified case, and then maybe do "adjustments" on the results that compensate for any real-world differences.

Thanks.

 

[Donald Qualls]

How old is that Analyser?

I ask because it seems like it may predate common use of multi-grade papers.

Difference in exposure for various densities on variable contrast paper depends mainly on the color of the light (how much blue, how much green), while that was a built-in characteristic for graded papers. That ISO(R) figure doesn't seem like something you could readily publish for VC papers...

 

[ic-racer]

ISO(R) is a slope, so you can get a ballpark figure with some trigonometry. Of course, every contrast grade for which you calibrate will have a separate ISO speed and contrast.
Not exact but it can give you a ballpark figure.

 

[removed account4]

dkonigs
have you been to the website or emailed the manufacturer ?
rh designs might have the info you seek.
http://rhdesigns.co.uk/darkroom/html/user_calibrations.html
John

 

[dkonigs]

As I do more research on this, I think I've come to the conclusion that the exposure for D=0.04 cannot really be derived from the paper datasheets and has to be determined experimentally. Of course its entirely possible that Ilford/Adox/Foma/whoever has the data handy, as their datasheets do contain graphs that can't be drawn without it. (Though its TBD as to whether I can get them to actually send me this information.)

That being said, I absolutely can take measurements to figure out what RH is using as their "baseline" value. (I already have a very rough idea, from some tinkering/measuring I did today. Though I'll need to collect a lot more data to be confident in it.)
I was just hoping there would be a better way.

 

[koraks]

As I do more research on this, I think I've come to the conclusion that the exposure for D=0.04 cannot really be derived from the paper datasheets and has to be determined experimentally.

This is correct. I've gone through a fair number of paper datasheets and none give absolute exposure information. At best they give iso R and relative spectral sensitivity.