Proper use of a Color Densitometer for B&W Negativesgreenspun.com : LUSENET : Large format photography : One Thread
When using a color transmission densitometer that has red, yellow, blue and white channels, what is the correct way to read density on B&W negatives? I've heard that Pyro negs should be read on the blue channel - why? What difference does it make to read between one of the color channels or the white light channel? Thanks!
-- Pete Caluori (firstname.lastname@example.org), August 16, 2000
Pete, where did you get those colors from? Is this a Macbeth unit and you're stating the color of the dots on the turret or something? Those units would typically have cyan, magenta and yellow dots to signify the color of the dye you would be reading. If you didn't know this, you might figure they are blue, red and yellow respectively.
The dot that is NOT colored would typically be what they call a "visual response" mode; it gives a broad spectral coverage and is what should normally be used for B&W negs.
When you use one of the colored responses, they are typically very narrow spectral bands, depending on the "status" of the response. Status M is for color negatives, Status A is for slides or reflection prints. However, since silver (in B&W) is not very spectrally selective, you should get very nearly the same density readings with any of the response functions.
-- Bill C (email@example.com), August 16, 2000.
Thanks Bill. Yes, it is an older Macbeth densitometer and the colored dots could very well be cyan, magenta and yellow. They're faded now and appear red, blue, etc.
-- Pete Caluori (firstname.lastname@example.org), August 16, 2000.
Use the plain or visual mode for most negs. If you're reading negs developed on pyro or that otherwise have a strong yellowish stain you'll notice a significant difference between the visual and blue/cyan filter readings; actual printing density on VC paper will fall in between.
-- John Hicks (email@example.com), August 16, 2000.
My Macbeth densitometer has red, green, and blue looking dots on the left and right side of the knob that selects the channel. At the bottom, in between these two rows of dots, there is an orange looking dot. On mine (which obviously may be a different model from yours) the instructions say to use the orange dot for black and white.
-- Brian Ellis (firstname.lastname@example.org), August 17, 2000.
make sure that you calibrate it first with a known density calibration negative. I purchased mine as a step wedge from a company called Stouffer. There should be a button on the back of your unit that will allow you to calibrate to the known density wedge. Kevin
-- kevin kolosky (email@example.com), August 18, 2000.