Article

Filters and the Digital Camera

You may have thought that using filters was a  thing of the past, as we can do so much in editing now. However they still have both a part to play when we are taking photographs and after in editing.

The most likely filters that are used today are the circular polarising filter and the graduated neutral density filter. However we can also use the array of filters that used to be used for black and white film if we wish. In fact those with Nikon cameras like the D300 have a range of built in filters for black and white photography.

The circular polarizer, usually screws on the front of your lens into the filter thread, but versions are available that can be fitted into a holder that can also be used to hold Graduated filters.   It looks like a sunglass lens, and cuts out half of the light so requires one stop extra exposure,   however your camera meter can meter through it without difficulty and take care of this for you. The circular polarizer is different from a linear polarizer. The filter has a part that is fixed and a part that allows the rotation of the filter, it has a different effect when it is in a position and rotated at 90 degrees.

The circular polarizer has a range of uses, these include:-

• Making white clouds stand out against a sky that appears more blue

• Seeing further through mist or haze

• Allowing you to see through the surface of water and photograph swimming fish

• Reducing reflections

• Increasing reflections

To get the effect with the sky try to shoot at around 90 degrees to the sun, so the sun is about level with one shoulder or the other, the effect is reduced as you swing towards the sun or directly away from it. You can see the effect through your viewfinder as you rotate the filter slowly to get the best effect.

To see through the surface of water or not and see very strong reflections depends on the rotation position. You will find that the best effects are obtained at specific heights of the sun and angles of approach between you and the water.

The effect of reducing and increasing reflections can also be used far more widely, for example reflections in windows, paintwork and the like.

The graduated neutral density  is also dark, like sunglasses, but is rectangular, dark at one end filtering out to be light at the other. It can be held directly in front of the lens but is usually slid into a holder that is fitted onto the filter holder thread. In most cases the dark end is at the top and is slid down so as to correct the difference between excessive brightness in the sky and lower areas. This allows the sky to stay intact in high contrast shots where often the sky would be blown (burnt out white). Neutral density filters come in a range of strengths (darkness) and you can use more than one at a time.

Of course they can also be applied in other ways, if the excessive brightness is from another direction or to get an effect you want. Coloured graduated filters can also be used in the same holders to get special effects like sunsets, or increasing colours in specific situations.

Like the polarizer's, graduated filters can be metered directly through the lens.

These in theory are the main two filters that we still need to use today when taking photographs as most others can be simulated in software later.

For black and white photography a range of filters could be used to improve the contrast in some situations.  The effect is to lighten colours that are the same or similar to the filter and darken opposites.  A good example of this is the control of contrast in the sky, using a yellow filter darkens the blue, orange has a greater effect and a red gives it a near storm like effect. Each of these colours also help progressively to see through mist.  Some situations we don’t consider today, were a problem for black and white photographers, for example often a red rose was about the same shade of grey as the green leaves, making them all but disappear. The solution was to use a green filter that made the greens lighter, and red darker and now the rose would stand out. The green filter can also be used to improve skin tone in some situations. Today you can still use filters on your camera to get these effects, and you may find that your camera has this built in, examples that do include the Nikon D80 and D300 cameras, in these cases you can just select the filter that you want and it is applied digitally when the camera is in black and white mode. When shooting in Raw, you can turn this off afterwards and even get back to a colour photograph if you wish.

Filters used in editing can also do the same and if you use Nikon Capture NX or NX2 then you will find this is a central feature of the black and white filter that converts your colour photo to black and white. You can select a filter of any colour and strength and see the effect as you play with it. Adjusting brightness and contrast at the same time. Incidentally there is also a colour contrast filter that allows photographs to stay in colour but for you to have a similar effect of the relative brightness of colours based on the same principles. Capture NX also has graduations, so many of the effects that you can achieve with neutral density graduated filters can also be achieved after the event, but of course cannot reduce the difference from extreme brightness and darkness that can be outside the tolerance of the sensor or film.

Within the Filter Section we have a range of articles on the filter types above as well as many more. We also look at the practicalities of filter holders and the cost of different sizes and systems, a good place to start would be in the article Filters - What you need as this has direct links to other articles.

See also: Filter Section for more articles.