By Paul Tyler
Last month we discussed the three primary colours and how they relate to the finished result of your pictures. I promised this month to explain in more detail how colour film actually works. I must assume you have a basic grasp of how black and white films work and produce a picture.
Although the chemistry of colour film is far more complicated than than that of black and white the principles are much the same. The idea that a full range of colours can be produced by just adding 3 primary colours leads to the possibility of making a colour picture out of three black and white negatives. (Your television picture, and this monitor produce the full range of colours using just three colour guns.)
Each negative would have to contain all the information about one
of the primary colours in such a way that any other colour could be produced by
a combination of the primaries. Early colour cameras produced so called
negatives by analysing the subject into its red, green and blue components.
These were then recorded on three black and white photographic plates, and a
special additive viewing system used to recombine the images into a colour
picture.
A far less cumbersome method is suggested by the subtractive principle. Instead of additive primaries, the images could be produced in the subtractive colour primaries made out of dies, then the final image could be viewed by laying the layers on top of each other and viewing the result with a white light. Hey we just invented colour pictures! No someone else got there first! This will work for both transparency and negative film. The image would appear blue where there was a combination of cyan and magenta because red and green would be filtered out!
Colour Film for slides and negative for prints consist of three layers. Each has an emulsion layer just like black and white film. Each layer is converted to a dye image at a stage during development thus arriving as the same effect as the three separate images we spoke of earlier. The top layer is sensitive to blue light, the second to green and the third to red. Light from the subject is recorded on the appropriate layer. Red light will pass through the first two layers and only affect the last layer. While yellow being a combination of green and red will record on both the second and third layers. With modern film there is far, far more chemistry involved, but the basic way the image is produced has not changed.
There are obvious differences in each manufacturers methods and this accounts for the fact that different film will respond to different colours. If you look at a manufactures advertising you will see their adverts dominated by one colour usually. Kodak favour red because I find their film responds well. Fuji favour green as this film responds well to green. The truth is all the major films respond exceptionally well to the whole spectrum compared to ten years ago.
Colour Reversal Film (Tranny)
The latent image formed on each layer
of emulsion when the film is exposed to light are developed in much the same way
as for B&W film. Exposed silver halides are converted to black metallic
silver, giving superimposed b&w negatives. After the first development, the
film is exposed a second time to fog the unexposed silver halides. These days it
is done with a chemical agent rather than whopping the light on for 10 seconds.
The second exposure is needed to provide a latent reverse image which gives a
positive rather than negative image. The film is then immersed in a second
development bath and this develops the newly exposed crystals into metallic
silver. Now comes the clever bit! At the same time dye couplers are activated.
These form three dye images of different colours wherever the development is
taking place. The blue sensitive layer becomes yellow. The green sensitive layer
becomes magenta and the red sensitive layer becomes cyan.
Finally the film is bleached to convert the metallic silver back to silver bromide, then fixed to convert the bromide to soluble salt. There you have a pretty good reproduction of the image in colour in positive format.
Colour Negative Film
Working with negative film allows the photographer a little more leeway as there are two stages. The developer performs exactly the same task as the second developer in the reversal process. It converts the latent image to black metallic silver
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| Always have your camera set to a ball park setting so you don't miss those paparazzi shots! |
and activates the dye couplers to give the dye colours at this stage. As no reversal has taken place the colours are therefore the negative colours. Again the unexposed crystals are washed away like fixing a B&W film. The colour negative film has as you would have seen an orange colour which is called the mask.
The advantage of this film is that the whole process is repeated onto paper which has very similar properties and a positive print is produced. By the introduction of filters into the enlarger the colour of the finished print can be controlled by the printing process.
So that's how it works, but what does it mean?
Well obviously with reversal film you only have one chance to get it right and that's when you press the shutter release. Tranny film has notoriously low threshold for over and under exposure, and really you have to get it right. When you do, tranny film has such bite and colour saturation. Colours have a real vividness that captures the beauty that you see with your eyes. Get it wrong and it's really wrong. One big advantage that tranny film has though is it can be over or underexposed by a good couple of stops, (that's the whole roll I'm talking about) and when you take it to get it processed they can push, or pull the processing to compensate without too much loss of quality.
So let's say you had planned a shoot and have ten rolls of 100ASA film, but
the day is really dark and dismal. You can push it to 200ASA and as long as you
tell them when they process the rolls it will be fine. (As long as each exposure
was
nearly perfect for 200ASA)
With negative film there is a far wider latitude for cocking up on your exposure. You can probably get away with a whole stop, maybe even 11/2 stops either way without losing that much in the picture. I have heard talk of being able to go as far as two stops out, but I have experimented and at two stops the prints are certainly starting to look muddy, or lacking contrast..
The rule must be to get that exposure as close as you can every time and then you will not have problems. The biggest problem with negative colour film is it is almost impossible to look at the neg to know if the picture is a good one. Look at the negative above. Click on it to see the full size positive image. You have to get everything right to take pictures like this. I do know people that can reverse the colours in their head and see, but they are few and far between. You will certainly need a contact sheet. This also allows you to guestimate the colour cast that each picture has. I said I wouldn't get into printing and processing, but just let me say each manufacturer has a start point for filtration for each film type that gives a starting point to account for the orange mask.
So remember all film has a certain latitude and if you go over, or under by too much you will lose the sparkle and lustre of the finished picture. With negative film only so much can be done in a darkroom to save a badly exposed print. If you stick to one film brand and type you will find you will get used to what it will and will not do. I know it sounds strange to say, but if you keep swapping brands you will never achieve great results. Professionals always use the same film. So much so if Fuji make changes to their brand I will use two rolls just to experiment. I will take a set subject using 1/2 stops in each direction to two full stops, then look at the processed results. I now use Superior regularly when using 35mm and personally with my kit find 1/2 stop over exposure gives the best results for me. You know your camera and lenses from constant use, and it should be just the same with your film.
If you have your films processed by someone else then again this is another variable. Shoot off three rolls of film and send them to three different labs. Obviously try and keep the shots very similar. Then choose the best. I often do this as I find labs can vary dramatically due to staff changes. E6 labs (Tranny) tend to be more geared for the professional with far more constant results. I would suggest that if you go to the expense of hiring a model and maybe a studio it seems sensible to pay the extra for professional processing with your negative film.
©Struthers Web 2000