Densitometer for B&W Negative

Can any transmition densitometer be used for reading b&w negative densities? I h ave made a series of exposures for zone I / film speed tests as laid out in A.A. 's "The Negative". The only lab on the island that has a densitometer, has an "R GB" unit. (what ever that means.) Will this RGB unit do what i need? I read something about an "RGB" densitometer somewhere, either here or in a book, and now I can't find the thread or article. I researched here, and skimmed back thr ough The Negative., but can't find RGB mentioned. As I'm new at this, (zone syst em, and Large format), all help is greatly appreceiated. dee

>> Will this RGB unit do what i need? <<

Probably. Basically, color densitometers usually have options that allow them to see narrow spectral bands (ie, colors). The one they called "RGB" probably actually measure the density of cyan, magenta and yellow dyes in color films. More than likely, if they read your film density for you, you'd find that all three sets of numbers are almost identical. Try it and see. To get the most accurate B&W density reading, you could average the three colors, but again, they're probably almost the same value anyway.

Some densitometers used in colour processing labs don't give a direct reading in conventional density units (D). Check that you can get a proper density readout before you pay good money to use the machine.A properly calibrated RGB or colour densitometer should read a silver image density exactly the same on all 3 channels. The only thing that might affect the readings is the base colour of the film, or dye left in the emulsion.The usual recommendation is to use the green channel for measuring B&W, but in theory at least, the blue channel should respond more like B&W printing paper.

The lab has a color densitometer. The color densitometers I've seen (which isn't very many), including the Macbeth that I own, all have a setting for reading black and white. If you can look at the lab's densitometer, rhere should be a wheel or slide or something that can be turned or moved to the color settings or to the black and white setting. On mine, there is a wheel with two sets of red, green, and blue dots(one set for transparencies, the other for negatives) and then a kind of pale orange setting. The pale orange (i.e. the one that isn't red, green, or blue) can be used for black and white readings.