Filters – the basics

Once you become hooked into the world of photography you can’t escape the lure of the filter, writes Andrew James.

For years filters have provided photographers with a means to get more creative with their photography and an excuse (if we really need one) to part with even more of our cash! The simple fact is, some filters are useful and, at times, essential items. However, some filters are better at attracting photographers than providing a genuinely useful weapon in the battle for better photos. So it pays to know which ones you are most likely to get good use from.

Filters also tend to come in and then go out of fashion. If, like me, you’ve been a keen photographers for 25 years or more, then it’s a fair bet that you will have a number of filters in your collection that never see the light of day any more. This can simply be down to how digital has changed the way we work or, as I said, how fashions for a style come and go. For example, unless you are (or possible were) a cameraman on Top Gear, there is no place in my humble opinion for a Tobacco Grad. This reddish-brown graduated filter has been used many times to add oomph to a sunset or sunrise or simply to paint its heavy handed colour across an ordinary grey sky. Trouble is, it never looks natural. My view is, leave well alone.

The other really out of fashion filter is the soft-focus filter. Loved in the 1970s when it seemed for a while every single portrait taken was through a soft focus filter, these days it is to my knowledge, rarely, if ever used. I actually own one of these. I have no idea how I came to be in possession of it but I can honestly say other than a brief session out of curiosity a few years ago, it has been gathering dust in the bottom of a box ever since. RIP. Admittedly I also once owned a Tobacco Grad and used it. I was young and foolish. I’ve learned the error of my ways. Double RIP.

Of course, these days we also have filters in our software. This is a whole subject on its own so, for this general skills article, we’re are going to concentrate exclusively on physical filters that you fit on your lens. And the ones that are genuinely useful.

Using a ND Grad in this shot helped to maintain details in the lighter areas.

Filter sizes
On the subject of fitting them on the lens, this is a good place to briefly touch on an important aspect of filters for anyone who has never used them before. For every day use there are two main types of filters. One is the screw-in type. They are circular and screw directly onto the front of your lens. The other is the rectangular slot-in type. These are held in front of the lens by a special filter holder. The filter holder is, in fact, also screwed in place on the front of then lens so really, whichever type you are going to use, you need to know the filter size of your lens. It’s easy to find out if you don’t know. Just look at the front of your lens and there, written in millimetres around the edge, will be your filter size. It will usually be preceded by this symbol ø (diameter). Incidentally, it’s also usually marked on the inside of the lens cap so if you can’t find it on the lens itself, take a look here.Just as an example I’ve picked up my 17-40mm wide-angle lens and there on the front is the mark ø77mm. So any filter I screw to the front of the lens must by ø77mm or it won’t fit. If I want to fit a rectangular filter then I will also need to make sure that my filter holder comes with an adaptor ring that is also ø77mm.There are also drop-in filters for long lenses. Instead of screwing onto the front of the long telephoto lens with its very large front element, they drop into a slot closer to the camera itself and we’ll touch on these on page 2.

Okay, that’s all pretty straight forward. If you are thinking of buying filters for the first time you can now work out the filter size for each lens you own, except you’ve also just discovered they are all different! What now?Well that’s just how it is I’m afraid. Lenses tend to have different sizes because their physical sizes are different. That said, you can be lucky as there are some standard sizes of filter fit. For example, while my 17-40mm Canon lens is ø77mm, so is my 70-200mm. Typical filter sizes you may find are 46, 49, 52, 55, 58, 62, 67, 72 and 77mm.

You need to know the filter size of each lens.

As a rule, I favour using a filter system (with a holder and adaptor rings). It’s simply more flexible. Perhaps the only exception to this would be if using a polariser or a UV filter. We’ll come back to the polariser later but let’s clear up whether a UV filter is a requirement. This is a clear glass filter that is designed to cut out UV light and can, in principle, be attached permanently onto your lens. The trouble is, I can’t see the point.

They really don’t do anything worthwhile and you are just putting more glass than necessary on the front of your lens. There is an argument to say that, if nothing else, they will protect your front lens element from scratching and smearing. Yes, this is true or you could just take care and try not to scratch or smear your lens in the first place. Use the lens hood when you think you might be in a situation when scratching from twigs or general foliage is possible! I’ve also heard it said that if you drop a lens with a UV filter on it the filter may take the impact and save the lens. Well, it might but it probably won’t. I once dropped a telephoto with a UV attached (back in the film days when they were a bit more useful) and both were smashed in an instant. I cried for a bit that day.

A filter system is often the approach favoured by landscape photographers.

Which filter make?
We can’t pick the filter make for you. You have lots of options out there and looking at my motley collection of filters built up over many, many years I have filters from Jessops, Kodak, Cokin, Tiffen, B&W and Lee. Filters are often expensive and it’s tempting to go for something cheap and cheerful assuming they all do the same job. They don’t. Some are better made and therefore last a lot longer, plus of course you also need them to do the job for which they are sold and some aren’t quite as good at this as others.

I’ve not used every single filter made and this isn’t a review so I am not going to compare them side-by-side. I will just say this. You get what you pay for and in my opinion it’s a false economy to go ultra-cheap with filters. While some of the more expensive makes, such as Lee Filters, may have prices that initially put you off, they do last if looked after properly and you shouldn’t have to buy a filter again for years – unless you are daft enough to drop them down the side of a cliff into the sea. Yes, I also did this once. I cried a lot that day.

Circular Polarising Filter
I have a big and expensive circular polarising filter – the 105mm from Lee – so it doesn’t screw directly onto my lens but rather onto a special screw attachment on the filter holder. Most polarisers will screw directly onto the lens itself or, for the longer lens there is a drop-in type. Polarisers are very, very useful and can do things that it is impossible to recreate in software. The most obvious affect of a polariser is the darkening of blue skies and maximising of contrast between that blue of the sky and the white of clouds (as you can see left). Polarisers need to be rotated to find the optimum effect and this blue sky/white cloud look is best on a sunny day when the lens is roughly at 90 degrees from the sun. Simply point it up in the direction of the sky and turn the filter until you get the effect you desire. Be careful though. You can actually over-polarise a blue sky to the point where it will go almost black and this never looks good.Polarisers will also reduce glare and reflections. On a sunny day with lots of green leaves in the shot, a polariser can be used to temper this glare and increase the saturation of the colours as a result. If you’ve ever thumbed through a holiday brochure and come across a picture of boat appearing to float on invisible water in some idyllic Greek harbour, this has been achieved by using a polariser. The reflection has been completely removed by the polariser so the boat just hangs there and makes you want to book a holiday, apparently. A polariser can have a similar effect on glass or any shiny surface so it really is a hugely useful filter. Because of the way it controls light, a polariser will typically reduce an exposure by about one stop, so you need to be aware of this, especially if you are using it handheld. But as you will mainly be using it in sunny situations it’s generally fine. Incidentally, you may see linear polarisers for sale. You don’t want these, you only want a circular polariser.

A circular polariser is a very useful filter to own.
Using a polarising filter has intensified the blue sky and made the clouds pop.

ND filters 
Not to be mistaken for ND grads, an ND is simply a filter that is totally covered in a tint. The ND stands for Neutral Density so a proper ND filter will have no colour cast and therefore no affect on white balance.

They come in different strengths and are used to hold back light and therefore extend exposure time. I have two and three stop Neutral Density Filters and will occasionally use them for subtly adding some movement to a landscape shot when otherwise it’s too bright to achieve the slower shutter speed I require, even at a small aperture. Are they essential? No. Useful? Yes…

The other time I might occasionally call them into action is when working in a studio, again for the simple purpose of holding back light to increase exposure times.

A straight ND filter for reducing exposure time.

Here’s an example of a three stop ND being used. In this first shot, although it’s low light, I can’t get a shutter speed slow enough even at ISO 100 and a small aperture to blur the water as I’d like. But, add the three stop ND and I can slow that exposure down sufficiently to blur the water in the second shot. Scroll between the two shots to see the difference it makes.

ND Grads
Without doubt these are my most used landscape filters. I have a complete set of both soft-edged and hard-edged ND grads. Like a normal ND they are neutral so do not affect the WB of the shot. Let’s look at the hard-edged ND first…

A hard-edged (also called straight-edged) ND grad is a rectangular filter where half of the filter is tinted and half clear. I have three in my collection – a one stop, two stop and three stop. Are they essential? Yes, if you are a regular landscape photographer, although you can get away with just the soft-edged if you want. I use them when I am photographing a scene that has a clear and uninterrupted division between land (or water) and sky. For example a simple seascape or perhaps a photo of the Norfolk Mountain Rescue Team in action, like in this shot below! See that straight dividing line between the land and the sky? It’s perfect for a hard-edged ND filter. You can also combine a hard-edged with a soft-edged if you want.

Soft and hard-edged NG Grads are useful to have in your kit bag.
A soft-edged ND is a filter with a feathered tint, so that it starts darkest at the top and graduates down to clear by halfway. They are useful in almost any landscape situation but are better than a hard-edged ND when there is something such as a mountain or building is protruding upwards into the sky because the darkening effect is feathered so less obviously affecting the object closer to the horizon line. I've used a 2-stop ND grad in the shot below taken at Elgol on Skye.

Using ND Grads
With your filter holder in place it is easy to slide the ND grad filter into place in front of the lens using the guide rails provided on the filter holder. Always use the rails closest to the camera and if your holder takes more than one filter then make sure both edges of the filter are in the right rails. Looking through the viewfinder or by using Live View will show the effect it is having so it’s pretty easy to position them over the right area. Knowing what strength to use is also fairly easy. First of all point the camera down at the land so the sky is out of frame and look at the exposure, making it a mental note of it. Now point the camera up at the main part of the sky and look at the new exposure. Calculate the difference between the two. So, for example, let’s say you metered off the darker land and got an exposure of 1/6Osec at f/11. Then, when pointing it at the sky and keeping the aperture at f/11 you had a reading of 1/500sec then the different would be three stops (1/125, 1/250, 1/500). In this case you would use a three-stop ND grad filter (0.9 in Lee Filter language). Of course you can also check the effect on the LCD and study the histogram too.

ND grads don’t just have to be used to mask the sky. I’ve spun the filter holder round many times and positioned the filter over bright water, snow and even white sand. You can also use more than one filter together, as long as you have a filter holder that fits more than one. Yes, you can physically hold a filter in front of the lens but it’s awkward and not recommended. It’s far too easy to move the camera and spoil the shot when you do this! Only do this as a last resort.

Big Stopper
The name Big Stopper is actually a brand name of the long exposure filter sold by Lee and other makes are available. Essentially it is a 10-stop filter. This means that it will hold back 10 stops of light and therefore increase the exposure time a lot! You either love its effect or hate it. I’d urge you to give it a go, you’ll love the results on waters, clouds, even fields of flowers or crops that are moving in the breeze. Lee also do a Little Stopper that is a 6-stop filter. Here’s a quick sequence of what a Big Stopper can do…

The standard shot taken without a Big Stopper attached.
The next shot has been taken with a 10-stop Big Stopper. The river water has smoothed out so the reflection of the tree is more obvious and the clouds in the sky are blurring. However, the raw shot has a blue colour cast. You can correct this in software or manually set the White Balance to 10,000 Kelvin at the time of taking.
The blue cast has now been corrected with colour temperature set at 10,000K.

Filter issues
Vignetting: The biggest complaint I hear from people using a polarising filter is that they can see darker edges at the corners of their images. This is vignetting, where the filter itself is registering on the edges of the image. It can occur when using wide-angle lenses and is frustrating. If your filter vignettes there is little you can do about it, except lose a portion of the wider focal length until the vignetting stops! Manufacturers have tried to come up with solutions. For example, Lee now produce a slimmer 100mm polarising filter and slimmer adaptor rings so the filter is held closer to the lens element. Having tried both set-ups, I can tell you this works. Where my original 100mm polariser always vignetted from about 20mm, with the slimmer version I could zoom right out to 17mm without an issue.

Lens Flare: It’s true that when using a filter or a series of filters on a lens then there is a greater chance of lens flare occurring. Not all lens flare is a bad thing, from time to time I actually quite like it in the shot but when you don’t want it then it is a pain. But lens flare is pretty easy to sort out simply be shielding the top and side of the lens during the exposure. I use my hand or often one the rectangular pouches I keep my filters in. As long as you are aware of the potential of lens flare to spoil a shot you can usually eradicate it easily enough. Flare can also be exacerbated by dirt and dust on the filter so make sure you keep them clean.

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