Exposing & Printing

Exposing & Printing

Filtration and time.

Whereas with B+W we were just concerned with the time of the exposure, when exposing colour prints, we also have to take the colour balance of the final print into account. This may involve a little bit of maths. I am sorry, but there it is. Its only a little bit. :)

   If you have an colour enlarger, or an enlarger with a colour head, then lucky you! The rest of us have to buy 'colour printing filters' to correct the colour balance of our colour prints.

  You may have used similar filters with black and white papers, if you used to use 'multi-grade' paper, where the contrast of the photograph could be set by the colour of the light you shone onto the paper.

  These filters are generally placed above the lens, between the light source and the condenser. There is generally a draw for them there. If there is not, then *try to make one!* since below the lens filters, of optical quality are going to cost a fortune.

  Anyhow, colour printing filters come as a set of densities between 5-50 in each of the secondary (complementary) colours. The filters are used in conjunction to alter the light source to correct the final print for the negative. This must be done for each print, and may vary somewhat between rolls if your process is not very standard yet.

  The filters often come a little too big, and so must be cut to size, however the left over strips can be made into an overlapping grid, which can save you a large amount of time when you are searching, by trial and error, to get the right colour balance. This is actually an advantage we have over those with their fancy colour enlargers!

The colour balance is found using test strips. I have seen well practised eyes do this just by looking at a neg, but dream on, its not going to happen that way for us...

I hate doing test strips and so, try to get away with just one, per print. With the grid, and a little practice this can be possible... place the grid either in contact with the paper or, in the tray above the condenser, and then perform a standard B+W teststrip exposure, for time. From the resulting print you should, with a little calculation be able to adjust the filter pack and time exposure to create a good print.

  How does the filter pack work?

  The filter pack contains cyan, magenta and yellow filters, however, you will be able to correct most colour casts without the use of the cyan pack.

  That said, it is very important to remember that you are effecting the ratio of cyan light, whenever you change a magenta or yellow filter. Always think of the ratio as C:Y:M, forgetting the Cyan component is a major obstacle to understanding how the filtration works.

  This exposing process is called the subtractive method, it works by giving one exposure to the paper, and altering the ratio of the complementary colours within that single exposure.

  It is also possible to expose using the additive method, with this method, you give three separate exposures through the primary colours. The filters for the additive process must be of optical quality since, they must be used below the lens, due to the fact that the lens will bend the different colours of light, slightly differently.

  The additive method will not be described here, since, it is now very rarely used, and having used both methods, I too find the subtractive method superior, not just for gaining control of the colour balance, but also due to the inevitable enlarger shake between exposures with the additive method.

  Although not helpful to your understanding of the subtractive process the following guideline is very useful:

  To correct a colour cast, increase/use a filter of the corresponding colour in the filter pack.

  As stated above, do not think about the above statement, it will only confuse matters. Save thinking it all out to when you can actually perform the process! (maybe while you're stuck developing 100 prints).

  So, sorting the colour balance, is possible via altering the densities of magenta and yellow filters. The cyan filters should not really have to be used at all.

  However, here I actually depart from the standard line on this matter, and would recommend to beginners the use of the cyan filter pack, since without the knowledge that you are altering the ratio of 3 colours, the whole exercise *can* become too complicated.

  For example, to correct a heavy cyan cast, you would reduce the yellow and magenta filters in the pack, this works since the untouched cyan light, is now increased by whatever you took from the magenta and yellow values. How much easier, if we allow the novice to actually use the cyan filters, so that he understands that he must increase the cyan ration to achieve the same effect, remembering all the time that for a heavy cyan cast, everyone would be forced to use the cyan ones.

Oh, and remember to expose the right side of the paper! It is *so* easily done in the dark, and is such a waste of your time. If in doubt, wet, (not lick!) your finger and thumb and gently pull at the paper, the sticky side is the emulsion.

A page from James David Chapman's website. Located at: http://www.users.globalnet.co.uk/~jchap/ Site mirrored here at: http://www.j.chap.btinternet.co.uk
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