Wow! What a lively discussion this is turning out to be. Firstly I must explain that whilst I have worked in a professional photographic lab, Im not actually trained in things photographic, Ive just learnt on the job, so to speak.
Ive had a bit of a think about this subject, I have been processing my own personal colour prints in my own darkroom since 1988, prior to that I did Cibachromes in the old 8x10 drum on the kitchen sink, plus a long forgotten Agfa colour process, that lasted about 4 years before it died.
I have been, like most of you, on a continual learning curve, sometimes a reasonably expensive learning curve. Ill set the scene, regarding what I know about some colour analysers.
There isnt any electronic analyser that can give you correct colour, before you tell it what the correct colour is!
In a nutshell, this is one of the major obstacles encountered by people new to colour printing. A person new to colour printing doesnt know what is correct, so they purchase an analyser to tell them what is correct, only to learn that they have to tell a machine something they dont know, so that it can work!
There are quite a few different types of colour analysers I have used, with the exception of one type, all require you to analyse each colour channel one by one. This is quite doable, but trust me it can be tiring, as well as time consuming. The exception to the rule is the Original Jobo Color Star colour analyser.
This analyser measures all three colours at the same time; I believe it is able to do this because it has three separate analysers working at once. The Color Star is so called because there is a star of coloured LEDs with two sliding levers allowing you to calibrate the analyser to a light temperature reading in literally 10 seconds. I believe the later 1000 2000 and 3000 Color Star analysers, work in the same manner. I dont know this, as I have never required any more colour analysing power.
I have used quite a few different things to obtain reasonably easy colour printing, some were a help, and some were really helpful. Things finally started to come together after a telephone call one very late winter night to Bob Mitchell in the USA, this was 1996. The late Bob Mitchell was quite a darkroom guru, inventor, and photographer and also wrote quite a few very informative articles for Photo Techniques magazine, usually about colour printing.
Bob had invented another useful gizmo; he called it a, Colorbrator. The Colorbrator is not a colour analyser. Rather, it is simply an accurate means for calibrating your analyser hence the name: COLORBRATOR.
Im not sure if the Colorbrator is still available, but if they are, get one. Basically it is an instruction booklet, with an actual colour corrected colour print stuck to the front cover.
Included in the kit:- a special colour test negative, which will produce a trial print, which will display an organised array of 49 colours, an image D-Max display of 16 grey values and a special segment for skin colour.
You also get a Neutral Comparator, which is a piece of grey card with a small hole at one end. By superimposing the comparator over your test print colour array, you can easily find a correct grey. The actual piece of colour array, which produced the perfect grey on your colour paper, is the piece that you tell your analyser is a grey you wish to produce.
The Wallace Expo/Disc is a calibrated light filter diffuser, designed originally to turn your, in camera reflected light meter, into an accurate incident light meter, it does this perfectly. The accuracy of the Expo/Disc can be shown by the data sheet, which came with my 52mm Expo/Disc. The sheet tells me that the transmission, which is supposed to be 18% ± 1/6 stop, had a deviation of 0.77 from these parameters, quite accurate for a cheap mass-produced item. The deviation of the colour transmission on my filter is:- .00 R .00 G .01 B which is basically nothing. It really is as true a grey, as you will get, for colour calibration.
After a re-think for the less experienced colour printing fraternity out there, and especially for Tom, as he is the original person I responded to, this perhaps, may be a more clear set of steps of how to get quite reasonable, but extremely repeatable, colour printing accuracy.
First and foremost, only use one type of colour negative film, develop it consistently, or get a lab that is consistent. Select one type and brand of paper, which means Fuji or Kodak. Select one type of paper chemistry. My personal experience with colour negative papers in my own home darkroom with Agfa, Fuji and Kodak papers regarding consistency, is that Kodak is the most consistent manufacturer out there.
Assuming you either dont or cannot obtain a Colorbrator, you have to get a correct colour balance for your system somehow. I shot pictures with a Kodak colour chart and grey scale from one of the Kodak colour printing books in the scene. I selected a clear sunny day with the exposures taken either mid morning or mid afternoon. The reasoning for the time the shots were taken is to allow light to fall on my models clothing. Early in the morning or late in the evening the light travels through quite a lot of atmosphere and the colour temperature of this light, isnt what daylight colour films are balanced for. The angle of late morning, midday, to early afternoon light, doesnt allow the enough light to fall on my models clothing for me to get a reasonably good colour rendition in the darkroom.
Take one or two frames of your model, then slide your Expo/Disc onto the lens, point the camera half to the sun and half to the blue sky. Have the camera on automatic everything, fire the shutter. I use aperture priority on my Nikon F3HP camera here. Take some more pictures of your model, this will ensure that your grey negative is in this section of frames. Develop the film.
Next, take any of the frames with your model (or whatever) place it in the enlarger and somehow get a correct 8x10 colour print. View your print(s) under various types of light, tungsten, fluorescent and daylight. You will find that the print(s) that look quite good under all types of light are probably correct, or about correct, regarding colour balance. If you are happy with your print, then you are almost there.
Set your enlarger filtration and timer, to what produced your perfect print. Which may have been 10 seconds at f8. Next do a colour contact of your roll of film, be that 135 or 120 using your exact same settings. You may find you have to pull or push 1/8 of a stop as this is a contact, not a projected print. So, to pull 1/8 of a stop expose at 9.2 seconds @ f8 or to push 1/8 of a stop, expose at 10.8 seconds @ f8. Once you have this contact sheet, you will be able to see subtle density differences between frames, this is a great help to the home darkroom worker.
You should now have a very, very good enlargement of a single frame, plus a better than usual colour contact sheet, of your roll of film.
Next, without changing any filtration, place the Expo/Disc negative into the enlarger and turn it on, place the analyser probe directly under the centre of the projected beam, open the enlarger lens so the maximum amount of light is projected. Turn all darkroom lights off, switch on the (in my case) Color Star analyser and slide the levers until all coloured LED lights are off. This has told the analyser the correct colour, note the settings. On my analyser I also have an exposure (density) setting. Close up the enlarger lens to the correct f stop, which in this case has been f8, slide the density lever until the time of 10 seconds shows, note that setting also.
The next thing, is to test your system. Take a fresh roll of film, go out into the wild world and bang a few frames off. However, every time you have a new light situation, take a frame with the Expo/Disc attached in the middle of the session.
Develop the film, then hit the printing department. First up, compose one of your images as you would like, then replace that negative with the Expo/Disc negative, slide the analyser probe directly under the centre of the projected beam, turn the enlarger on.
Now, you should open the enlarging lens to allow the maximum amount of light to hit the probe. Ensure that the analyser settings are correct, you did didnt you? Turn all lights off, turn the analyser on, now adjust the enlarger settings until all the analyser lights are off, you have correct colour. Next, set the enlarger lens f stop to f8 and check the density reading on the analyser. This density reading could be anything from 5 seconds to 10 seconds or more. You have a few options regarding exposure. You can open the aperture, adjust the exposure, or add or subtract neutral density in your enlarger head, to arrive at a suitable time. Any of these should work without any problems. You could also print at what time the analyser suggested, this could be 8.4 seconds or 11.8 seconds or anything inbetween or outside this set of imaginary times. I have found very little to no colour changes apparent to my naked eye, when changing exposure times willy nilly, in a colour negative darkroom procedure
Anyway, now you can whack in your award winning negative, focus, expose, develop, then sip on a mug of hot chocolate, whilst you are viewing a near perfect, first go, colour print!
Mick.
Ps:- Hopefully this works, it's Friday night after work and I sat down and did this in word in one hit, if it doesn't make sense, give me a hoy.