Manual for the Beseler PM4L color analyzer
I could not find the manual for this model but I have used it for a long time and familiar with its operation. I know quite well how it works so I would like to post some information on this unit so some of us here can make use of the information. I won’t mention the way one should use the analyzer as I have heard and read many people’s opinion on whether the color analyzer would really work. Many don’t think it would work so I wish not to explain on how to use it but rather on how it works. Knowing how it works each of us can devise ways to make it works for us even though some of the applications weren’t intended by Beseler.
1. It seems that Beseler used the same PMT (photo multiplier tube) to sense light for all models of their analyzer. On lesser models the PMT is housed in a box with the color selector and is used as the probe. On the PM2M and PM4L this box is housed inside the cabinet right behind the color selector knob. Light is fed into this box via a fiber optic cable and the probe is made so that it can be turned toward the lens for cosine correction. When measuring a spot that is not directly under the lens, position the probe so that the arrow pointing toward the lens and then slowly turn the probe toward the lens until you have the most light coming into the probe. When you have more light into the probe the reading would be more toward the negative side as the meter is indicating filtration or lack of light. The color selector will position the corresponding filter in front of the PMT to read light of only one color channel. Red filter for cyan, green filter for magenta and blue filter for yellow. The output of the PMT is very much proportional to the amount of light striking it.
2. The output of the PMT is then routed thru a bunch of circuit that has diodes in them. I still not yet understand how these circuit works but they make this signal becomes approximately proportional to the logarithm of the light intensity. This signal is then fed into a comparator circuit that compares it with the voltage set by the programming knobs on front of the analyzer or in the program cube is if the selector is set to module. When you switch the filter selector the unit also switches in the corresponding resistor for the color channel. The front panel setting resistor is the combination of the coarse and fine adjustment.
3. The output from the comparator circuit is then fed into the meter for readout. This readout is calibrated so that to show density or CC unit. On the PM2M and the unit is set for white light it can be used to measure the negative density. To do this first set the programming knob so that the meter reads zero without the negative. Then put in the negative and position the probe where you want to measure density. Till the probe toward the lens so that you have the lowest density. This is supposed to be the density of the negative at that spot. I have found that the reading is a bit lower than what I read from an X-rite densitometer. It’s about 90%. The PM2M meter also is marked in seconds and normally you would program for the meter to read the the time it takes to correctly expose the known negative. On the PM4L when you switch to white channel the signal is fed thru a converter to make it once again directly proportional to the light intensity and the meter would readout in seconds. I sometimes bypass this circuit so that I have the meter readout in density because it’s more useful to me.
I hope it would help some of us here. If any of you have any more questions I would gladly answer.