Quote Originally Posted by 2F/2F View Post
Not to go too much off topic, but can someone explain what "RN" means, and how the numbers relate to contrast?
Since I generated the post, I'll answer it the best I can.

If doing paper sensitometry, graphing the paper curve and such, the Range Number is found by measuring the width of the paper's Exposure Scale Value (ESV or I believe otherwise stated by Mr. Benskin as the LER for Log Exposure Range, although I have not seen that acronym before, I believe that is what that is, seems to make sense).

The width is measured by subtracting the Log Exposure Minimum (Emin) for reaching the highlight density limit from the Log Exposure Maximum (Emax) for reaching the shadow density limit. Those limits, according to Anchell, are set by the ISO at 90% of Dmax for Emax and .04 over the Dmin for the Emin of the paper.

The difference multiplied by 100 equals the paper's ISO Range Number. That ISO Range Number correlates to an equivalent contrast paper grade. For example, for a manufacturer to sell a paper as a grade 2, then it must have a RN between R95 and R115. Divide that R# by 100 and you will have the width of the paper's ESV on the log exposure scale of the paper curve.

A different RN can be associated (with your printing system i.e., paper, light source, filter, developer, toner) with each contrast filter or filtration setting in your arsenal. The RN is then bounced against a Contrast Equivalent Chart established by the ISO, according to Anchell. That's how it is related to paper contrast grade as I understand it. I included a graph from the book I'm using as an illustration; sorry for the blurry scan.

Why do I feel this is important? Because I use the ZS as my method of film and development testing and I test very strictly with it (whether one agrees with that method or not, I don't find it relevant). I want to know with the paper I'm using in my printing "system" what contrast filtration available to me provides a standard grade 2 paper contrast. Just because you have a #2 contrast filter does not mean you are getting a paper contrast grade of 2, although it could if found by testing your printing "system".

I discovered that it is not a filtration setting of 2, but rather a setting of 4 that provides a paper contrast grade of 2 (R95 to R115) with the Oriental paper I tested. The filtration setting of 4 produced an ISO RN of R110.

Now, I don't know if there are multiple ways to determine the RN and quite frankly, I don't really care as I don't have time or materials to carry on a battery of tests. I understand this fully and don't have any inclination to test a multitude of different ways to determine it or to see that another method is better or more right. I find this test method to be very easy to carry out and understand.