Paper grade definitions

[srs5694]

I was wondering what the definition is of particular paper grades (grade 0, grade 1, etc.). The reason is that I've been using tables of filtration values to paper grades for my color head (a Philips PCS150; Philips published two, one for Kodak papers and one for Ilford papers) for some time, and although these tables work well for rough approximations, they don't seem to be quite perfect for the papers I use. I use the "constant exposure time" tables, but the exposure bobs up and down a bit as I adjust the contrast using these tables. I'd therefore like to construct my own table, but to do this I need to know how paper grades are defined or measured. I've got a Stouffer step wedge. Would I make prints from this, adjusting filtration until a particular number of steps are distinguishable, and call that grade n? If so, what's the mapping of number of steps to paper grade? If this is the wrong track, could you point me to the right one? Thanks.

 

[gary mulder]

http://www.butzi.net/articles/vcce.htm

The article describes the process of calibrating the filtration much better then I can ever hope to.

 

[keffs]

Another option is to use filters. These are more accurate than using the colour filters in a dichroic head.

Steve

 

[Photo Engineer]

Grade refers to the contrast or mid slope of the charateristic curve of the paper. There are discussions about this in "Post Process" by Ctein and in Photo Techniques about 2 years ago in an article by Dickerson and Zawadski.

Basically, a grade 2 paper has a mid tone slope of about 2.5 measuring Density vs Log Exposure. Higher grades have a higher slope and lower grades have a lower slope.

PE

 

[srs5694]

Thanks for the references! I'll read the link and, if necessary, locate and buy the back issue of PT or the Ctein book (or maybe just get the Ctein book from a library).