Which camera filters are actually worth buying?

Filters are one of the few areas of photography where the physical accessory genuinely beats the software, and only in two specific cases. Knowing which two saves a drawer full of glass.

Step by step

1. Understand what a polariser does.Light reflected from a non-metallic surface — water, glass, wet leaves, a painted car, haze in the air — becomes polarised. A polarising filter can block that polarised component, so reflections disappear and the colour underneath appears. This is a physical selection at the lens and there is no software equivalent.
2. Use a polariser at the right angle.The effect is strongest when you are at ninety degrees to the sun and weakest when shooting directly towards or away from it. Rotate the filter and watch the viewfinder: the sky darkens, reflections vanish and return as you turn it.
3. Know the polariser's costs.It absorbs one and a half to two stops of light, so shutter speeds lengthen. On a very wide lens it darkens the sky unevenly across the frame, because the angle to the sun changes across a wide field of view. And it removes reflections you may want — water can lose its shine entirely.
4. Understand neutral density.A grey filter that reduces light without changing colour, so you can use a slow shutter or a wide aperture in bright conditions. It is how you get silky water at midday, blurred crowds, or f/1.8 portraits in full sun.
5. Choose an ND strength by what you want.Three stops for modest movement blur, six for obvious water blur in daylight, ten for clouds streaking over seconds or minutes. Variable ND filters are convenient and can produce a dark cross across the frame at their extremes.
6. Treat graduated ND as a landscape tool.Dark at the top, clear at the bottom, to hold a bright sky back. Useful where the horizon is straight, awkward where it is not, and increasingly replaced by exposure blending — but it works in one frame, which matters when there is movement.
7. Decide honestly about protective filters.A clear or UV filter protects the front element from grit and knocks and makes a lens easier to sell. It also adds two air-to-glass surfaces in front of everything, which on a cheap filter means visible flare, ghosting around lights and reduced contrast. If you use one, buy a good multi-coated one and take it off when shooting towards a light source.
8. Skip the effect filters.Warming, cooling, colour and soft-focus filters solved problems film had and digital does not. White balance and editing do all of it better and reversibly. Star and diffusion filters remain a matter of taste but are easy to over-use.
9. Buy the size for your largest lens.Get filters to fit your biggest filter thread and use cheap step-up rings on the smaller lenses. One good filter across a kit beats four mediocre ones.

Tips

• A polariser on a wide-angle lens over a blue sky produces a dark band across part of the frame. Use it at standard focal lengths and longer.
• Take the polariser off when you do not need it. Two stops of light and a slight softening are a real cost for no benefit indoors.
• Cheap ND filters often introduce a strong colour cast. It is correctable in RAW but tedious across a whole set.

Common mistakes

• Leaving a cheap protective filter on permanently — Every photograph passes through it. Poor coatings cause ghost images of bright lights, veiling flare and lost contrast — and the damage it prevents is rarer than the damage it does to picture quality.
• Trying to reproduce a polariser in editing — A polariser selects which light enters the lens. Once a reflection has been recorded there is nothing underneath it to recover. This is the one effect that genuinely has to happen at the front of the lens.

If it doesn't work

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