Color Process Computer...
On one of my "free darkroom stuff" pick-ups, I picked up an Optographic Lab Color Process Computer. I'm wondering if anybody has an information on this machine as I cannot find anything. I have just started doing RA-4 in my home darkroom and this thing might be fun to play with, if I knew how it worked. There are no probes or anything, it simply has a slot to insert a negative and several knobs. I'll post some pictures later if they will help. Perhaps there is a similar device out there that is more common that I can read up on? I'm definitely NOT expecting this to remove the burdon of learning how to use my color head and adjusting the filtration. Thanks for any help you all can give.
I suspect it was designed to work on analysing a 'standard' negative.
The content of the negative I don't know anything about.
Some analysers integrate by way of diffusion to arrive at a neutral grey.
Others may follow a more of a process strip approach ie perhaps a dark spot to judge developer (or more specifically, exhausted bleach) activity by, a light spot to look for staining, and a grey spot to check for the right dilution/time/temperature/replenishment rate of the developer, and perhaps to also judge the exposure filtration and lamp intensity/aperture/time settings.
A picture, or at least naming the knobs, and the increments they are divided by may help my general explaniations become more specific.
And, yes, Colour printing means training your eye, despite what all sorts of toys are there to help.
my real name, imagine that.
Thanks for the reply Mike. I'll post some snaps tonight. It does have a grey card, a diffuser and separate knobs for yellow, cyan and megenta (and another that I can't remember the descriptor). The display is an analog needle with a 0 in the middle with numbers ascending/decending on either side.
After using my black and white darkroom for many years, I decided it was time to expand my horizons! RA-4 is so much fun, but my brain has to be reprogrammed for CMY
Generic to all RA-4 printing
For RA-4 - set the neg/slides switch on the unti unit to negs.
Set the cyan filter on you head to zero. It is used when you print from slides.
The fine/coarse switch on your unit tells you to read the upper (fine) or lower (coarse) CC units scale
The third scale on the analyser reads in stops, and is used wehn the selector switch is set on delta D.
Usually when RA-4 printing, you use the amount of light (time and aperture, filter pack denity, as well as overall denisty of the negative) to set the density of the print, and the red level of the print.
You balance the blue level using the yellow filter, and the green level with the magenta filter.
The drag is that filters are imperfect, and also add overall density as thier colour intesity varies. Yellow varies little in overall denisty; magenta denity is more substantial.
The key to analysers functioning is that they presume that all scenes integrate to neutral grey.
Most scenes taken outside in a natural setting do.
A photo of someone standing against a building painted red or something else really filling a scene doesn't.
This in the ananlyser trade is known as 'subject failure'.
So you start by having a known grey neg analysed.
Are you sure there are no trimmer pots on the back, or a small panel to be removed to set the balance on this calibration negative?
The other option for you might be to have a grey card stuck in the front. I am not clear from your unit where the neg gets held, or where the unit gets its light to analyse with.
Its own anuminum sheathed glow lamp with a little hole in the top in the front diffuser chamber? l am not clear on how this may work.
I am not clear if when you turn your unit on if it supplies its own light,or if it uses the enlarger's light to read though the negative.
The usual way to use a generic single channel analyser is to presume that exposure is fixed, at say 5 or 8s. Then the variable in exposure is a function of only neg denisty and aperture.
The switch on the analyser is set at Ddelta , and the measuring probe is used to drive the meter needle to read from the lower calibrations on the dial. You open or close the aperture until the meter zeros.
Then switch to yellow delta. Read off the fine or course scale, to see the adjsutment needed to make the measured negative print as grey. Adjust the filter pack/dial in or out yellow to zero it.
Next move to Magenta delta. Manipulate the filter setting until it is zeroed.
Then go back and check aperture. The first pass through the analyser, making gross filter adjustments, will mean the efefctive light path denisty has changed , and needs fixing to accomodate for filter density.
The safest way for you to figure out how to use this analyser is to make a shot of a grey card filling the frame in exterior light as a part of a film you get processed. It need not be in focus, but do have it fill the frame.
Then without the analyser, make a perfectly grey print using the said grey test neg.
It may take more than one night. Don;t be frustrated. Getting started in RA-4 takes time, mostly to teach your eye to see colours and density separately.
I would start around f/8, 8 seconds, 80Y and 50M as a strating point if you are using Kodak RA-4 optical expsoure balanced paper, and RA-RT chemicals at 38C.
Once you have your perfect print, change nothing on the enlerger. Then use the negative to see how the analyser reacts. This no analyser for the first good print is needed to calibrate almost every analyser I have ever come across.
I hope these scattered comments get your thinking brain in gear. Good luck.
my real name, imagine that.
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Thanks Mike. A lot of good information here. I am guessing that the negative should be inserted into the slot between the knobs and the logo. There is a small light tube (looks like a fluorescent lamp) inside the unit that would light the negative from behind so the sensor could read it. I'll go over it again to see if there are any calibration things on it. There is a grey card on the front of the unit, which is also lighted, I guess, from the tube light. This thing has no probe, nor a place where a probe would have been connected, so I assume that it does not utilize an enlarger at all and merely reads a negative inserted into the slot. That negative may be, like you suggested, a grey card shot to calibrate that film.
I'm having fun with color. It will definitely take time to calibrate my eye so I can figure out how to get a print where I want it. Thanks for you help again! I appreciate it.