OPTICAL FILTERS ARE PIECES OF glass or acetate which are placed in front of the camera’s lens while taking the picture, which allows the photographer to manipulate the picture before it reaches the camera’s digital sensor.

In the early days of digital photography, the death of the optical filter was widely heralded. Prophets of doom proclaimed that henceforth we would all be using Adobe Photoshop to do all colour adjusting and manipulation on the PC, rather than doing any camera-side filtering.

As time has passed, though, the new technology has settled into its own skin, and photographers have slowly but surely awakened to both the strengths and weaknesses of the two stage manipulation process where the image is created in the camera and adjusted on the computer.

One of my old photography gurus used to say that any photograph is only as good as the negative it comes from, and in the old days of red light darkrooms and wet chemical trays, this was certainly true. Start of with a bad negative, and you would have an uphill battle creating a decent print.

How much has things changed? Well, image manipulation has now become a lot easier, and much more accessible. No longer does the photographer need a dedicated room (or two) to do his printing. He can do it all in the comfort of his lounge on his laptop. But what he cannot do, is turn a bad original image into a technical masterpiece.

Sure, contrast can be changed and levels adjusted, but start with an overexposed sky that is burnt out to pure white, and no amount of burning in or darkening will ever bring back the detail in the clouds. There are also some things filters can do that just simply cannot be replicated in Photoshop.

The mighty polarizer

The polarizer has been the most faithful companion of the landscape photographer since time immemorial, and nothing has changed with the advent of digital photography.

A polarizer works by filtering out all the light waves that are vibrating on one specific plane. This sounds a little bit technical, but it is enough to understand that all the light that reflects of a shiny surface vibrates on the same plane, and a polarizing filter has the ability to selectively remove these reflections.

So, if you were photographing a glass building and were disturbed by the reflections shining off it, you would reach for your polarizer and moments later you would be able to make all the reflections disappear.

The effect also works on water, where reflections can be darkened, and on cars, where a nasty shine on the hood can often be eliminated completely. It works on people wearing glasses and on champagne bottles. The utility is endless.

But the most powerful effect of the polarizer filter, is in its effect on the sky. Because the blue element of the sky is basically reflected light, the polarizer filter can darken the sky while leaving the foreground and, importantly, the clouds untouched. This can often turn a quite bland photograph into a striking one. Darkening the sky will have the effect of giving more prominence to the puffy white clouds and can really lift a photograph. Replicating this effect in Photoshop is well nigh impossible, and even when achieved, is very, very time consuming.

Graduated Neutral Density Filters

One common problem often faced by landscape photographers, is that one part of a scene can be much brighter than another, commonly with the sky bright and the foreground about 3 to 4 stops darker, making it hard to get a correctly exposed image in one shot. The photo manipulation proponents would solve this problem by taking two pictures, one exposed for the sky and the second for the foreground, then later combining the two images.

This method has its failings. First of all, it makes the use of a tripod essential, because if the camera moves between the two exposures, it is that much harder to combine them afterwards.

Secondly, in many cases, and especially in inexperienced hands, the join between the two images can often look very unnatural.

Faced with a scene with a part in bright sunlight and another in shade, I would much rather reach for a graduated grey filter, which would allow me to capture a correctly exposed image for both parts of the scene with one click of the shutter.

The Grey grad, as it’s known to its friends, is a filter split in two parts, the one is made of clear glass, the other is a neutral density (i.e. colourless) grey, and slipping this over the lens, with the graduation placed on the horizon, and the clear half over the foreground, would result in a correctly exposed image without any post-capture manipulation.

Neutral Density Filters

Often a photographer would like to take a scene in a certain way, with a predetermined aperture, shutter speed and iso setting but the light at the scene might be too bright. In these circumstances, there would be nothing he could do during the post capture stage to rescue the image, but using a neutral density filter (which is basically a piece of grey glass), he would be able to limit the amount of light passing through the lens, and therefore obtain a correctly exposed photograph.

Close-up Filters

A close-up filter works like a magnifying glass and allows the photographer to take a macro picture with a standard lens. The effects of these filters cannot be replicated during the post-capture stage without cropping the image and losing resolution.

Filters for protection

In my time as a photographer, I have always tried to take very good care of my equipment, but on occassion I have knocked the front of a lens against an obstacle, and once I even dropped a camera. It is at times like these that I thank my lucky stars for the forethought of placing a UV filter on the front of the lens.

UV filters are pieces of clear glass that screw onto the lens, ostensibly to remove haze and UV rays (I have never been able to judge their effect). But they can also serve to protect the lens from dust, scratches and carless knocks. Take my word for it, do not leave home without a UV filter screwed to every lens you own.

Square Filters, Round Holes

For those occasions that you do want to use filters, you have two options. The first is to buy a screw-in filter, which would have to have the exact same diameter as your lens. This often means buying a filter for every lens you own.

The other choice is to buy into a square filter system, like the Cokin system, which uses pieces of square glass that slip into a holder which fits on various lenses via a doughnut shaped disc which fits on the front of the lens. This often works out cheaper if you own a number of lenses with a variety of diameter measurements.

Obsolete Filters

Yes, it is true, not all optical filters are as useful as they once were. Some, like colour correction filters serve no more purpose, as the technology has changed and allow us to carry a slightly lighter bag. Filters for black and white photography also fall in this category, as few people now shoot in black and white, preferring convert the image at a later stage. Special effects filters are also quite archaic, the starburst effect is much better produced on the computer than in the camera, and next month we will have a whole section on how to recreate the effects of a soft focus filter using an Adobe Photoshop technique.