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FILTERS

In Pics 1 & 2, You will see that some of the pencils,
which look totally different when viewed in colour,
have the same or similar tones when photographed
in monochrome.

For instance the orange & blue pencils (a) are easily
identified in colour but in monochrome they look very
similar, as do the other pairs (b & c).

Can you find other examples in the pictures?

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WHY DO WE NEED TO USE FILTERS?

As we have seen, with black and white film different colours may often have the same tonal value, in other words
appear the same shade of grey. With some subjects it would be difficult to distiguish between parts of the image.
Filters can be used to correct or modify the image

The following pictures, Pics 3,4,5, & 6, show part of the colour image converted to monochrome to simulate the
effect of filters on the tonal range.

Pic 3, Is a straight conversion, (no filter) note the fairly
wide tonal range from white through to black. Compare
this to Pics 4,5 & 6.

Pic 4, You can see the effect of a red filter on this image. Pencils which reflect red light :- red, orange, purple etc.
appear relatively lighter than in Pic 3, whereas the
blue/green range are darker.
Note the yellow, which has some red in it, has hardly
changed tone.

Pic 5, With a green filter, it is the green
parts of the image that are lighter while the red
parts,including purple, which has a lot of red &
blue, have darkened.
The light blue pencil pobably has
some green in it and is relatively unchanged.
Again the yellow is almost unchanged because
of it's green component.

Pic 6, The blue filter has darkened the red,
orange and yellow elements and lightened
the blue part of the spectrum.
Note the restricted tonal ranges when
a filter is used.

Note:- These examples have been produced digitally, to illustrate the effect of filters on an image.
The effect of real filters on film may not be quite so pronounced.
The actual colour range & density of filters varies, depending on the manufacturer and the materials
used to make the filter.
 

VARIOUS USES OF FILTERS:-

Apart from using a yellow filter for clouds, other filters can be used to good effect.
Green filters can darken a sky but lighten the landscape and foliage.
In Autumn a red filter will make the red and brown leaves stand out against a black sky with white clouds.
A pale green filter can often be used in portraiture to improve flesh tones.
An orange filter will improve the rendering of stonework, and the contrast of snow scenes. 
Use a filter of a similar colour to a flower to make it stand out from the background.
For example, a red filter will lighten a red flower and darken the leaves, making it stand out from the foliage.
Alternatively a green filter will lighten the leaves and darken the red flower.
Why not usea filter to separate different coloured flowers of similar tone, by darkening one and lightening the other.