michi-gap
Hello,
I’ve been looking into colour enhancement a bit recently. Unfortunately, I’m not really getting the hang of the filter settings, so I’ve been trying to find out more about tools that can help. I haven’t found any really good answers, though, so I have the following questions:
Unfortunately, I’m on a tight budget, so expensive colour analysers are out of the question – or are there cheaper ones that are any good?
Has anyone here ever used colour charts for this and can explain to me exactly how they work?
Michael
TR
I’ve only done colour enlargements once. You do know that it’s best to use a grey area on the negative as a guide, don’t you? If I were to do colour enlargements more often, I’d always place a small grey card at the edge of the subject, if possible.
And on the subject of analysers: you can pick those things up quite cheaply on eBay. Otherwise, all you need is a chart with a colour wheel showing the respective complementary colours.
Renate
Hello,
The samples must be viewed in dry conditions under a daylight lamp. Place the colour chart next to them. Look for an image on the chart with a similar colour cast. The filter values specified for that image must be added to the existing filter values (note the minus sign!). Colour charts can be found in many older textbooks.
A colour cast is always eliminated by increasing the filter values of the complementary colour or reducing the filter values of the unwanted colour. When enlarging negatives, only the magenta and yellow colour filters are used. Cyan always remains at zero. The packaging of the colour paper contains information on the base filtration. This should be set as the starting value and samples should be made based on this.
I have never used a colour analyser.
Best regards
Renate
hambo
Hello Michael
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I have to disagree with Renate on this. The filter colour is always the same as the colour cast. So if the image is too yellow, the yellow filter is increased.
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I’ll try to give you an overview of the process for producing a colour-cast-free print in just a few steps. It’s true that only yellow and magenta filters are used when working from a colour negative. To start with, choose a negative that contains both grey tones and bright white, such as an asphalt road or a white shirt, for example. A shot of a market or a pedestrian zone would be very suitable.
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Whether you start with the zero copy – i.e. without a filter – or go straight to 30/30 is up to you. Always write the filter settings on the back of the test strips with a soft pencil, in the order yellow, magenta and cyan. Then get to work and produce test strips with different exposure times or a step exposure. Only once you have found the correct exposure time should you start filtering.
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So, to recap: filter colour equals cast colour!
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Normally, there will be a yellow/magenta cast, which together produce a red cast. The filter colour is therefore red, which is composed of yellow and magenta. Now, test strips are exposed with increasing filtration. Assuming the print with 30 30 -- is still a nice red, then increase the filters in 10-unit increments. Hence, test strips with 40 40 --, 50 50 --, 60 60 -- and 70 70 --.
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If this is still not enough to eliminate the red cast, produce further test strips with higher filter values.
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Be careful, this is where it gets a bit tricky. If the filter setting is higher than the existing colour cast in the negative, the colour cast will shift to the opposite colour. I’ll quickly list the filter colours and their opposites (complementary colours) for you.
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Yellow --- Blue
Magenta --- Green
Cyan --- Red
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Once again, the filter rule applies here too. An example: a print with a filter setting of 60 60 -- now has a blue cast. You achieve a blue filter colour using magenta and cyan. But there’s another rule to bear in mind: you should never filter using three colours.
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In detail, it looks like this: let’s say the print has a blue cast of strength 10; this requires, written in the usual order of Yellow, Magenta, Cyan, the filtering -- 10 10.
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This is now added to the existing filtering: 60 60 --
???????????????????????????????????????????????????????????????????????????????????+-- 10 10
???????????????????????????????????????????????????????????????????????????????????-------------------
???????????????????????????????????????????????????????????????????????????????????? 60 70 10?
i.e. 60 yellow, 70 magenta, 10 cyan
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The smallest value is now subtracted from all colours: 60 70 10
??????????????????????????????????????????????????????????????????????????????????minus 10 10 10
??????????????????????????????????????????????????????????????????????????????????????????? --------------
???????????????????????????????????????????????? New filtering????????????????????? 50 60 --
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That’s a lot of theory, but unfortunately it has to be done. If the magenta filtering is too high, the colour cast shifts towards green, which is usually very noticeable on skin tones. The procedure is exactly the same.
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It would be helpful to make a contact print of the entire roll of film on colour paper. Filter this out to the extent that some negatives are already well filtered; then you can see from the others where the colour cast is heading.
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There’s one thing I haven’t mentioned yet, namely that the filters absorb light. For every filter you increase, the exposure time must be extended. There are tedious tables available from which you can determine the factor by which the time should be multiplied for each filter strength. A lab exposure meter is advisable here; something simple like a Jobo Comparator will suffice for now.
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The best way to proceed is to prepare the test prints for the exposure time at around f/11 on the enlarger. Then – and here’s a pro tip – remove the negative or simply pull the negative stage forward slightly, and then calibrate the exposure meter: place it on the base plate within the enlarger’s light cone and turn the calibration dial until it is balanced; on the Comparator, both diodes will then light up with equal brightness.
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If you now increase the filtration, place the comparator back into the light cone without the negative and adjust using the aperture; as light is absorbed by the filters, you will need to open the aperture, but there is scope for this as f/11 was the starting value. The exposure time remains the same! This has allowed us to compensate for Mr Schwarzschildt and his effect. Coloured paper reacts to a change in exposure time with a different colour cast, as the three emulations have different speeds. One less source of error.
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Right, good luck with your experiments.
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If you have any further questions, get in touch again.
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Regards
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Jürgen
ThomasPauly
One more point: unfortunately, filter scales are not standardised across manufacturers. Whilst there are textbooks and brochures that show graduated examples of colour casts and specify the corresponding correction filters in 10-step increments, in practice they are of limited use.
Simple analysers that only allow for average measurements are not necessarily ideal either. They cannot distinguish between colour casts and colour dominants. A large green meadow in the image is therefore interpreted as a green cast; the indicated filter (green) then results in a complementary (purple) cast in the positive. Furthermore, the shadows (which are generally less important to the image), as they allow more light through in the negative than the mid-tones (which are actually of interest), contribute disproportionately to the average measurement, which can be a further source of error. With this type of measurement, one can at best approximate the desired result and must then still carry out the fine-tuning using test strips.
Top-of-the-range analysers are very fast and allow spot measurements to be taken on a reference area, e.g. a grey card, even at high magnification levels; this is photographed at the start of a series of shots or included at the edge of the image.
If you work without an analyser, the magic word in colour processing is ‘consistency’. It is best to use only one type of film and paper and to buy a year’s supply of it. The materials should be stored in the fridge. It is also important to use a lab that carries out professional quality control of the C-41 process. If the factors relating to materials and processing are largely constant, all that is needed is to compensate for the colour temperature of the lighting used for the shoot. One then usually operates within a range that can be reasonably estimated with a little experience, so that the desired result is achieved with one or two test strips – even without an analyser.
The best introduction to colour processing that I know of is an Agfa brochure, which was published with various updates from the 1960s through to the 1980s. The explanations regarding filter selection remain unchanged to this day. Perhaps it can be tracked down second-hand somewhere.
Best regards
tepe
Gast
One more thing: unfortunately, filter scales aren’t standardised across manufacturers.
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To compensate, I have a conversion table for my Meochrome 2. As I also have ORWO/AGFA filters, this is quite useful for working according to the old ORWO instructions :-)
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Incidentally, the Fuji paper I’ve just bought didn’t have any base filtration printed on it.
michi-gap
Hello everyone,
Thanks so much for the tips! I’ll have a go at sorting out the filtering without the analyser first.
Michael
