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N.E.P.W. ONLINE TUTORIAL SERIES

 No.1. FILTERS

FILTERS and their uses, in Black & White Photography.

A Basic Introduction.



FILTERS,  usually thin discs or squares of coloured glass, gelatine
or plastic, are used to change or modify the tones in which the colours
of objects are recorded onto monochrome film.

Basically a filter transmits light of its own colour and
blocks light of the remaining colours.

A RED  filter blocks

GREEN & BLUE light

and transmits

RED light

A GREEN  filter blocks

BLUE & RED light

and transmits

GREEN light

A BLUE  filter blocks

RED & GREEN light

and transmits

BLUE light

A YELLOW  filter blocks

BLUE light

and transmits

GREEN & RED light

Because a filter mainly transmits light of it's own colour it makes those areas
on the negative darker, therefore the matching areas on the print will appear lighter.  

In other words, by blocking out part of the colour spectrum of the light
striking the film, the image can be modified to compensate for problems with
exposure, film characteristics, subject colouration or to produce special effects.
 
For instance, when photographing clouds against a blue sky the intensity
of the light from the clouds and the sky is almost equal, so the sky in the
resuting print will be a disappointing grey tone with the clouds hardly visible,
but by using a yellow filter to reduce the intensity of the blue part of the
spectrum, the sky will  appear darker, allowing the clouds to stand out.  

To Recap
A yellow filter will hold back the blue light.
With fewer silver crystals being darkened on the film these areas
will be less dense on the negative.
Conversely, in the print these areas will become darker.

To create a really dramatic sky then use a red filter.

NB. If including people, then a mid yellow filter is preferable
as it will not distort a person's complexion too much.

REMEMBER - TO LIGHTEN A COLOUR, USE A FILTER OF THAT COLOUR.
TO DARKEN A COLOUR, USE A FILTER THAT HOLDS THAT COLOUR BACK.