I’m sure most people use filters, whether it is the humble UV filter, or more specialised filters designed to create or enhance certain effects.

It surprises me though how many people are not sure about what filters do, or even how to use them properly.

So, here is a run down on what I believe to be the most important filters we should be considering. I’m going to leave specialist types like soft focus out - they’re more the trade of playboy photographers (unless of course you consider your fishing or hunting mate could benefit from a smoothing of wrinkles and blemishes?). I’m going to focus on filters for colour photography; filters for black and white photos are a completely different kettle of proverbials again.

Before getting into the specifics, the most important advice I can give is that your filter use should not be obviously noticeable. As soon as a filter gives itself away to the viewer we’ve lost the point of using it I believe. Subtlety is the key.

I’ll be talking about two differently constructed types of filters. The first and by far the most common is the circular screw on type. This is a glass filter that screws onto the front of your lens for a desired effect. The other is the 'Cokin' type which is a square, or rectangular, piece of plastic that slots into a filter holder on the front of your camera.

Firstly, it’s a good enough reason to carry camera filters in the outdoors, if for no other reason than as emergency sunglasses. I know of at least one chap who been able to tape polarising filters across his eyes as temporary protection from snow blindness! Here goes....

Skylight, or UV, filters
Well, if you own a camera chances are that you own a skylight, or UV, filter. Do you know why? More than likely the salesman sold you one when you brought the camera because “ you needed one”. What does it do? Well in my mind, it’s worth is not in the photographic benefit you’ll derive from it, but solely from the insurance benefit. Smack your lens on a rock (not an unlikely thing in the hills believe me) and a $20 piece of metal and glass martyrs itself for your prized camera lens. It also unselfishly takes a heap of abrasive ‘cleaning’ that would render your expensive lens front as useless as a really useless thing if you insisted on scrubbing away with toilet paper to dry a lens as some folk do.

Their real use is attempting to reduce any haze that strong scattering of UV light may cause. The skylight filter is essentially a UV filter with a slight pink tinge in the glass. The idea here is to neutralise the slight cold cast that UV light may produce in your images. So the message here is to keep a piece of glass between your delicate bits and anything that could be out to damage them - a cheap and relatively important piece of gear.

Polarising Filters
Moving right along to a more functional piece of equipment, the polarising filter is an absolute must for the outdoors photographer, simple as that.

I’ve listened to salesmen in shops explaining that you need one of these to get a really blue sky in your photos. They’re right on that count, but there are a heck of a lot more benefits (and pitfalls) to this filter that you need to know about. Lets understand it’s operation first.

Basically, on a fine day all light is traveling down from a single light source, the sun. When it hits objects it is reflected and scattered in many directions. When this happens, light may become polarised differently to that arriving from the sun. I won’t bore you with heavy physics explanations here, but simply explain it by saying that light waves may vibrate at one angle and when they’re been polarised they will vibrate at a different angle. The beauty of a polarising filter is that it can filter out light that is polarised at a given angle, by rotating the filter. This gives us the ability to control problem light, such as that reflecting upwards off water, exactly the same job a pair of fishermans’ polarising glasses does, allowing him to see through any reflections on the waters surface.

The polarising filter looks like ‘black’, or dark, glass and is labeled PL or C-PL. It is different to all other filters because it is designed to be rotated once it is on the camera lens; it is also relatively more expensive than others. The main use that people put this filter to is to produce beautiful deep blue skies and enhance the appearance of cloud in the sky. This happens largely because of the increased contrast range because of the deeper blue. For this they are superb and almost mandatory I think, especially in the high country.

The use of a polarising lens is simple, screw it onto the front of your lens, compose your shot and then rotate the filter until you get the desired effect you’re after - deep blue sky and pure white clouds (note that some lenses rotate the filter when they focus and this might adjust the filter from how you set it), and take your shot. All this is simple, but it relies on a couple of bits of important information.

Firstly, the polarising filter is a very good light robber, it will reduce the amount of light entering your camera by 2 stops, i.e. it will only allow a quarter of the available light through. Fortunately this is not generally a problem on a bright sunny day, but bear it in mind. Note that if your camera (as most modern cameras do), meters through the lens then you don’t have to worry about exposure details. If you use a lightmeter though you’ll have to deduct the 2 stops of light from your reading. The second important piece on info relates to the effectiveness of the filter. If you are facing towards, or away, from the sun then the filter will have minimal effect. If you are facing at right angles to the sun you will get maximum effect (the deepest blue sky etc.).

Besides creating a beautiful deep blue sky, you will find if you play around with this filter that tree foliage will go a magnificent deep green colour, especially at right angles to the sun. You often see luscious deep green forest photos and wonder why you can’t get them like that? Well, the polarising filter may help you. In the same way that this filter will take glare off the surface of water, it will take the glare off plant leaves. The result is often a huge increase in the colour saturation of the photo. Classic foliage for this is silver, black and mountain beech trees as they have very small shiny leaves. Get right angles to the sun and turn your polariser and watch then change from a silvery green to a deep lush, almost edible, green. In general, the polariser will increase the colour saturation of your photos. Along with this though is an increase in contrast and you will lose a bit of detail in any shady parts of the image.

Most people use their 'pola' filter only on fine days. Few know it’s benefit on overcast days. If used it will greatly increase your colour saturation, however, you’re probably going to need a tripod as there is a lot less light about on these days, and remember it’s a great light robber. Pola filters are very helpful if you’re wanting to photograph with a slow shutter speed on a bright day, say water movement. Use them as a neutral density type filter, as they will cut down two stops of light and allow you to use a shutter speed 2 stops slower.

There are actually two types of polarising filters, Linear (PL) and Circular (C-PL) polarisers. Basically, the type of camera you use dictates which you need because the linear type (although cheaper) can confuse the autofocus and exposure sensors in modern auto everything cameras. The circular type can be used on any type of camera but is a bit more expensive.

Price depends heavily on the size, make and type (PL, or C-PL). You’d expect to pay around NZ$30-40 for a 49mm PL filter, and around $50-70 for a 58mm C-PL. I highly recommend that if you’re on a tight budget to cast around for second-hand filters. You can normally pick up very good condition (unscratched) filters for about 1/4 of retail price. Some camera shops have boxes fill of them - ask for a sift through.

Warm-up filters
The light we see has a temperature to it. Instinctively you know what I mean - light from the setting sun has more of a yellowy tinge than the harsh cool sun late in the morning; the evening sun is warmer. Likewise, bright halogen car headlights seem a lot more bluey-white (colder) than say the light of a candle (warmer). I remember a very effective TV advert selling home insulation, Pink Batts I think. Side by side sat the Pink Batts house and the other non-insulated house. The main visual difference was that the warm house was painted a slight pink colour and had a cosy yellowy light bulb hanging in the window. The cold house was painted a soft blue and had a stark bluey-white light hanging in the window. Boy, it was so effective that looking at the cold house gave you the shivers! The purpose of a warm up filter is to help achieve the same thing as the Pink Batts advert, to give your images a warm alluring feeling (if that’s what you’re after). It is designed to subtlely shift the colours in your photo away from the colder blues and into the warmer yellowy-browns.

There are two main types of warm up filters. They’re coded as either 81 or 85 series, and they’re coded for their strength. 81 series type are amber in colour, while 85 series type are more pink. My advice would be to go for the 81 series. The strength of the filter varies with the letter after it; 81a is the weakest and 81d is the strongest. Generally I would not be interested in using a warm up filter stronger than 81b as it starts to look unnatural, however there is considerable difference in strength between manufacturers. It is worth experimenting with warm-up filters to find your preference - some people won’t like any.

Although, if you’ve got a hunting mate that likes to take their shirt off occasionally, and he or she has an ‘office’ suntan, then an 81d might be worth the investment! The result will be white chicken flesh changed to well grilled with the screw on of a filter! Price is much more attractive than polarisers, these cost around $25 for a medium sized one.

Grey Grad, or Graduated Neutral Density filter
This is a very useful filter, but the draw back is that it takes some effort to use in the field; it’s fiddly and easy to muck up. Here’s the theory...

When we’re photographing a landscape photo, we’ve often got a big contrast in brightness between the land and the sky. Normally the sky is much brighter, especially if it’s an overcast day (because the sky will be a bright grey colour).

Because photographic film is not as good at recording the huge range of brightness that our eye can deal with, some of the photo will inevitably be over or under exposed. This is where the grey grad. filter is very useful.

Essentially it’s a filter that is clear at one end and tinted grey at the other, the filter graduates from no filter, to a dark neutral grey. The idea here is that we can move the filter up or down in it’s holder so the tinted portion covers the sky, and the clear bit covers the landscape. It’s like selective sunglasses. The sky will now be closer in brightness to the land and your film will be able to record the scene with ease. Likewise you can use these filters to dramatically darken the sky, if you’re after more atmosphere etc. And there is a range of different coloured tints available for different tasks.

The most common make of these filters in New Zealand are the Cokin brand. They come in two sizes and are available in most camera shops. You will need to purchase a filter holder initially that screws onto the front of your camera. This opens you to a wide range of special filters that Cokin are known for.

To use graduated filters takes a little care. You must remember to take your camera meter reading off the land before you install the grey grad. That way the land will expose as required and the filter will not effect the reading. You must also take care when you have objects such as trees that extend into the sky (and therefore the darkened part of the filter) as the filter will make them very dark and unnatural. They are also excellent at picking up a static charge and will pick up dust and lint from all over the show, and you know how much lint you make when you’re in the hills! Oh, and they scratch very easily! Cost is about $30-35 for the basic size if I remember rightly.

Diopters, or supplementary close up lenses
While not strictly filters, these deserve a mention anyway. As detailed in the Macro (close-up) photography column (Dec’97/Jan’98), Diopters are a convenient screw on lens for close-up photos, not just a piece of tinted glass. They normally come in sets of 3 different powered lenses, +1, +2 and +4 power. These are very convenient to carry in the outdoors because they’re lightweight and versatile. You can check it out by clicking here.

General tips
As all camera lenses have different sized front filter treads, you might have to buy several sizes to cover all your gear (it does help buying the same brand though). You can however buy stepping rings which allow you to use larger filters on smaller lenses. This helps the wallet and also the weight of your back pack. Likewise, with the filter holder set up, such as Cokin filters, once you’ve bought the correct adapter, then the filter holder simply fits all lenses.

If you’re shooting print film, the machine that prints your photos from the negative can alter the colour balances. So if you’re using a warm up filter, the machine may automatically remove the slight amber cast. You should discuss this with the agent that develops your films. On the other hand, if you’re shooting slide film you can be sure that what you get back is exactly what you took.

As previously mentioned, many photographic shops have boxes full of second-hand filters. It is worth your while if you’re on a tight budget to have a fossick through these.

Well, get snapping, because as they say, the world looks much better through ‘rose-tinted’ filters.