Film does not `see' the world as we do. We see a scene bit by bit, our eyes adjusting for the varying colour. Daylight varies from blue through yellow to red, and even green in a wood but we see it as all the same. Colour film cannot do this. It will record a wide variation of hues from one scene at different times of day, often with amazing changes around dawn.
You can get pleasing results without filters of course and a colour cast however induced can add impact and atmosphere. The point is that with a few filters you can control the result.
Fitting Types
There are three main types of filter fitting; round glass screw on, round glass push on, and square resin which slides into the slots of a purpose made holder. Glass resists scratches better than resin, costs more and is optically slightly better, but you won't normally see the difference, except perhaps in the corners of the frame with a wide angle lens. Sheets of gelatine can be bought which you cut up to fit whatever holder you have. You can also get a square lenshood/holder from which four sprung filters can rapidly be swung into position. Ideal for different effects with groups of people and limited time.
When buying a filter system, buy it to fit those of your lenses with the largest front element. You can then use step down rings to fit smaller lenses. Bear in mind the widest angle lens you have. With wide angles, and particularly zooms, the filter holder can cause cut off in the corners. Check this by stopping the lens well down, (use the preview button); rotate square types checking the corners. Slight darkening with the square at its worst angle is usually acceptable but it is galling to build up a set of expensive filters, only to find they don't fit your latest lens without causing problems.
Filters for Colour Correction
As I mentioned, the colour of light varies. This is described by a number called the colour temperature, and often needs to be corrected to suit the film in use. Fit a blue filter to correct for orange artificial light and a warm up or straw colour to compensate for that cold or blue light found typically around noon time in shadows and in snow scenes. If the light is mixed, with, say, tungsten lit windows in a scene at dusk it is probably best to err on the warm side and allow the artificial light to appear orangey. Fluorescent light is the most difficult to correct as each type of tube is different. However, most modern shop and display lights are the same temperature nowadays. They appear green and need a magenta filter. If you use colour print film, you can let the printers correct the colours. I've heard Fuji Reala will even cope with mixed daylight and fluorescent but most others will show the difference.
One of the most useful is a graduated grey, this is clear on one half merging to a neutral grey on the other, and is available in different strengths. All films have a limited brightness range they can record, without either washing out the highlights or blacking shadow detail, colour slide film being one of the worst with a range of about 7 stops at best. Usually it's the sky that's too bright. The graduated grey can be positioned on the front of the lens to reduce the brightness to the film.
This is one situation where square filters in a slot are better than fixed round ones. The tinted area can be slid up and down to match the scene. Use the depth of field preview at the same time to see the effect at the taking aperture. You may find with lake and river scenes that another graduated fitted the other way up helps to darken a reflected bright sky, but fitting more than two filters will start to reduce image definition.
Filters for Enhancement
Often overlooked is the polariser. All light has a polarised content. Reflections on shiny surfaces are strongly polarised. These reflections, which cause a whitish glare on what we know is a coloured subject can be removed by a polariser. This effect can be varied from full to minimal, by rotating the filter as you look through the camera and view the difference it makes. (if you don't have an SLR just look through the filter then hold it front of the lens in the same orientation). Whilst full will give maximum colour saturation, the picture can look a little dead with no highlights in it at all, so it's often better to use it at less than full setting.
Blue sky can be darkened dramatically making white clouds really stand out, but only at or near right angles to the sun. Watch out for awkward density variations across the frame when using wide angle lenses in this way. The sky could appear unnaturally varied in density.
Polarisers come in two types; linear and circular, this refers to the way they work not the shape (autofocus and some clever metering cameras need circular types to work reliably - check your camera handbook, or ask a good dealer for the type you need).
Polarisers:
- lose about two stops of light, but this does mean they can be used as a neutral density filter as well;
- increase colour saturation of blue sky and brightly lit subjects;
- are normally made round in a rotatable mount (even with square filter systems);
- cut reflections on water and windows, but not from polished metal.
Coloured and Graduates
The first colour filters were used to improve black and white pictures. Early films were particularly blue sensitive. The negatives had dark skys, and the prints correspondingly washed out skys. This was corrected by fitting a yellow, orange, or red filter. Modern film behaves better, but even so blue sky can be darkened dramatically by using the same filters; red has the strongest effect. So, in black and white photography, coloured filters lighten their own colour and darken their opposite.
With colour film, the effect of strongly coloured filters is overpowering. Weaker ones can add colour for mood or effect. Blue makes things look cold or dark; straw looks like evening or Autumn. Sepia will mute colours and give a nostalgic feel while pink can look romantic, but a tobacco sky over a blue lake just looks odd.
Special Effects Filters
There is now a very large range of different effects possible, with star sparkles, diffraction, speed, fog, and soft focus just a few of those available. Most photographers go through a stage of experimenting with these, and produce all sorts of weird pictures in the process. This doesn't mean these effects should be dismissed, they do have a place with the right subjects but they won't make a poor picture good and are probably best used sparingly.
Another special effect is to use a slow shutter speed to blur moving water, or lose moving people in a time exposure. Although not it's only use, the neutral density, available in different strengths, allows this by reducing light to the film. These can also help if you find you have a very high speed film loaded and the sun comes out!
It should be mentioned that improvised filters can give excellent results. A thin smear of vaseline round the outside of a skylight filter can provide you with soft focus, as can breathing on front of a cold lens and shooting as it clears; a trick used by many professionals. More specials are fishnet tights stretched over the lens, and dimpled glass or bottle bottoms.
Having sunk to the level of tights and bottoms, I'll just leave you with a handy chart as a guide. This shows filter factors for separate meters. The TTL in the camera will compensate automatically.
| Lamp (Watts) |
Light Colour Temp. (°K) |
Daylight Film | Factor Stops | Tungsten Film | Factor Stops |
| 60 Houshold | 2800 | 80A+82B | 3 1/3 | 82C | 2/3 |
| 100 Household | 3000 | 80A+82A | 3 | 82A | 1/3 |
| 150+ Studio | 3200 | 80A | 2 | - | - |
| 150+ Photo | 3400 | 80B | 1 1/2 | 81A | 1/3 |
| Flourescent | "Daylight" | Fl-D | 1 | Fl-B | 1 |
| - | All | Polariz. | 2 | Polariz. | 2 |