Written by Kevin MacKenzie
Originally posted to the Canon EOS list in January 1997. Reproduced with permission.
The number one filter NOT to buy is a Cokin rainbow filter.
As a first start you will probably want to get a UV or Skylight 1A filter followed by a Circular Polarizing filter. If you only shoot colour negatives you could stop there. If you shoot colour slides you will likely want to add an 80A filter which corrects the colour of indoor incandescent lightbulbs to the correct colour for daylight balanced film. Next you will probably want to add an 81A filter which gets rid of the blue cast that is present in shadows (this is because the only light in shadows is reflected from the blue sky).
For black and white you will probably want to get a yellow and a red filter which control contrast very well. If you are interested in infrared photography, there are a couple of different filters to use there too. Some pass a little visible light to help in composing and focusing, others dont. Willem-Jan Markerink can help you in that department.
If you do a lot of landscape photography you may eventually want to buy a Cokin P filter holder (which holds unmounted square filters over your lens and allows them to be moved up or down and side to side) and two or three different Graduated Neutral Density filters (Cokin P size). Grad ND filters are used to darken only a part of an image such as the sky.
For landscapes, you may consider a colour enhancing filter which partly blocks dull and muddy wavelengths of light allowing more of the really vibrant (primary and secondary only) colours to pass to the film. These are also in Cokin P size and are expensive.
If you photograph indoors under flourescent lighting you may have noticed that the photographs are washed with green, especially in the shadows. This is because the spectrum of fluorescent light has a strong spike in the green wavelengths of light. You can use a four layer film such as Fuji Reala to get rid of the green or you can use a filter on normal (3-layer) daylight colour films. Fluorescent tubes come in two common varieties, daylight and warm (there are a few others that arent so common). For daylight fluorescent tubes use a Magenta FLD filter and a Magenta FLW for warm fluorescent tubes (some manufactures also make one for use on tungsten films).
A further complication arises when you wish to mix flash light with ambient fluorescent light. In this case you need to keep the Magenta filter on you lens and change the colour of your flash to match the colour of the fluorescent lights. This is accomplished by covering your flash head with a Green (CC03?) filter (if your flash head doesnt take filters just tape it on). This combination will expose your film with the right mix of colours. Since the picture is not taken through the filter on the flash head, it can be a cheap low quality gelatine filter provided that it is the right colour. With negative films (even the three layer variety) most of the green wash can be corrected during printing and so these filters may not be necessary for some subjects.
You will probably find, as most photographers do, that special effects filters are cheesy and give a cheap Hollywood look. The possible exception being centre spot filters which make the periphery of your picture a little out of focus while leaving the center sharp (also Cokin P size).
All this is worth about a million dollars so I would start with only the Skylight and Circ Polarizer. Look for used filters especially if you are not sure whether you will like them or not. You can usually find them for less than $2. If you like them, upgrade to a good one. The multi-coated filters are high quality glass (as opposed to plastic resin) and are coated with anti-reflective polymers which help to prevent flare.
Check the filter thread size of your current lenses, as well as those which you plan to buy in near future. For example, if you plan on sticking with Canon stuff you may want to buy your ring mounted filters in 58mm size and use a step up ring on smaller lens (55mm male thread / 58mm female thread). I say that because 58mm is a very common filter size for Canon EF lenses and the step up ring is only $10-$15.