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UV Filters: Cheap protection or expensive placebo?

Introduction

One of the more controversial topics in the photographic community centres around the use of UV filters as a method of protecting the objective element of a photographic lens from dust, grime as well as bumps and scrapes. The practice is quite widespread to the point that many camera shops will recommend UV filters when you purchase a lens (especially an expensive, higher-end one).

On the face of it, it seems like a good idea. Screwed into the filter threads at the front of your lens, the filter becomes the first point of contact should something unfortunate happen. However, whether it is actually a good idea isn't quite so clear cut...

What is a UV Filter?

As suggested by the name, a UV filter is a lens filter that prevents the transmission of Ultraviolet light, whilst not affecting the transmission of visible light. Like other filters like Circular Polarising Filters and Neutral Density filters, UV filters satisfy a creative purpose, albeit one that is not applicable to digital photography, as will be explained below.

If you're shooting a film camera, cutting down the amount of UV transmitted through your lens is a good idea, because film is sensitive to both visible as well as Ultraviolet light, which can result in unintended colour casts over your exposures. Interestingly on the other side of the spectrum, film is not generally sensitive to Infrared wavelengths, which is why you generally can't pick up an IR filter at the local camera shop.

In the general case, UV filters weren't needed for photography taken near sea level, but their need increased with altitude, where the extra UV could introduce a blue colour cast over the photo. Furthermore, excessive UV could manifest itself in exposures through the appearance of "haze".

Fortunately, a digital imaging sensor is much less sensitive to UV light than film, meaning that the actual need for these filters has vastly reduced. Furthermore, the ease in which any colour cast is corrected (often in camera through Automatic White-Balance settings, or in post-processing) means that in the unlikely event that a blue colour cast does occur, it is easily correctable.

However, UV filters are relatively cheap, and their effect on exposure as well as the eventual photo is relatively minimal, meaning that even with the widespread adoption of digital cameras, their use as a protective filter has increased.

The Protective Filter

I suspect that the rise of the protective filter has mirrored the rise of the digital camera, something that brought photography to the masses and put Digital SLRs into the hands of many hobbyists. High quality optics are as expensive as they ever were in the film era, and as people handed over large sums of money for longer or faster lenses, they obviously looked for ways of keeping their lenses in pristine working order.

Encouraged by camera stores (who earn a fairly large profit margin on filters of all descriptions compared to the tighter margins on camera bodies and lenses), people have turned to UV filters as a form of protection. The fitment of the UV filter is said to:

• Increase weather and dust resistance;
• Protect against dirt and grime as a result of people touching the objective element;
• Protect against flying, airborne debris; and
• Protect against impact trauma (drops, bumps and scrapes)

On the flipside, those who disagree with the use of protective filters point out that it seems counter-intuitive to purchase an expensive, highly engineered optic, only to introduce an extra unneeded glass element at the front. Furthermore, it is pointed out that the quality of the filter element is almost certainly nowhere near that of an expensive lens.

Weather Resistance

The first of these claims - weather and dust resistance - is actually not without merit. It is true that some lenses (notably the 16-35mm f/2.8L and the 50mm f/1.2L within the high end Canon 'L' range) require a filter to complete their weathersealing.

While this probably means that should the objective element come into contact with a lot of dust or water, it would be more resistant, effectively, it means that the lens is reasonably weathersealed (especially around the mount and barrel area, which is most likely to be exposed to water). Remember that weathersealed does not mean waterproof, and immersing a modern autofocus lens into water without a housing will almost certainly destroy all the electronics inside it (as well as encourage the growth of fungus).

The other factor to weathersealing is the camera body itself. Not all camera bodies are weathersealed - only the higher end Nikons and the Canon 1 series is weathersealed. Canon specify "increased moisture and dust resistance" for the 50D, 7D and 5D Mark II, but these cameras are still not weatherproof. Without a completely weatherproof system, having a weatherproof lens (even with a protective filter) isn't going to help you too much.

Still, if you work in places where there is a large amount of airborne water spray or dust, it may be prudent to fit a protective filter.

Protection against fingerprints and grime

While a protective filter will prevent people touching the objective lens element, the fact remains that, for the remainder of that session anyway, fingerprints will still be on the front of your lens. The best protection against such circumstances is to keep your gear out of harm's way to begin with.

Perversely, cleaning filters (especially expensive, multicoated filters) can be harder than cleaning a lens element with some microfibre and isopropyl alcohol. For some arcane reason, grime on multicoated filters tends to streak - although certain filters (eg. Hoya's HD series) tend to be much easier to clean than others (many users of Hoya's HMC filters have complained about streaks).

Apart from physically moving the camera away from curious fingers, a lens hood also offers good protection from fingers. Apart from protective qualities, a lens hood also helps keep out unwanted light, therefore increasing flare resistance and increasing contrast.

Protecting against flying, airborne debris

Unless you're using hardened filters (like the Hoya HD series), the use of filters to protect against flying gravel when shooting a World Rally Championship event is largely pointless. A piece of gravel travelling at a high enough speed to break your objective element is almost certainly going to smash through a lens filter, before hitting the objective element of your lens with its speed barely slowed. The glass shards that would result from a smashed filter would also probably scratch the objective element close behind.

Again, lens hoods present a much more elegant solution - especially the deeper examples fitted to telephoto lenses. A ultra wide angle lens - with its exposed element (Nikon's 14-24mm zoom and Canon's 14mm L ultra wide angle prime have elements that protrude so far forward they cannot accept screw-in lens filters!) is always going to be more susceptible to this kind of damage, and a wide-angle lens hood is basically next to useless. If you're shooting with a ultra wide angle lens, it's best to be careful and move the lens out of harms way completely.

Protecting against impact trauma

A lens hood is going to help you more than a thin sheet of glass if you drop a 600g camera body and 1kg lens by accident, simply by keeping the lens elements out of harms way. However, it's almost certain that in either case, you're going to damage something. Lenses are ruggedised to a degree (especially pro-spec gear) but a big drop is going to jolt something out of kilter. It's like dropping a mechanical watch or clock.

If you bump something out of alignment, you're going to have to get it fixed professionally - doing it yourself with some small screwdrivers is not recommended unless you happen to know exactly what you're doing. This is especially the case with modern, autofocus lenses with all sorts of electronics crammed inside.

A lens filter may help if you're in the habit of shoving your big telephoto through a dense bush or other something that will protrude through a lens hood. Generally, if you're doing this, you're probably taking photos of something you're not meant to!

For general use - you're better of protecting against bumps and scrapes on the lens by fitting a lens hood. Some lens hoods (notably the one on the Canon EF 24-70 f/2.8L) fix onto the main barrel of the lens, meaning that the extending, telescopic inner lens barrel is also protected from being bumped out of alignment.

Potential Problems

This is where the bad news starts for the filter advocates. While the above sections may have shown that filters can help with water spray and weather resistance, there is a price to pay - and that is that optical aberrations may occur as a result of that extra element. These problems include:

• Lens Flare: This can manifest itself as multicoloured spots or streaks across part of your frame, or merely as a loss of contrast. This is due to the light reflecting off the front of the objective element, into the back of the filter and reflecting back in an unpredictable manner.
• Potential Damage: If you do manage to break the filter, there's a chance the glass shards might scratch the objective lens element. In the case of a drop, a bent filter ring might make it impossible to remove the filter without breaking it completely. This is especially true for filters with metal filter rings.
• Chromatic Aberration and Distortion: Poor filters can introduce distortion and chromatic aberration, things that designers of higher-end lenses put expensive aspherical elements, fluorite elements and low-dispersion glass elements to correct in their lens designs!

Mostly, these problems can be avoided by fitting a good, high-spec filter. As with any good photographic gear, these filters don't come cheap. The high spec UV filters can cost well more than $100 (Australian). At one filter per lens, that adds up to a lot of money (especially given that the cheapest lenses start at around $150!). Quite an expensive solution, really...

In Conclusion...

To conclude, there are some valid reasons to fit a protective filter, but it's not the reason that most people give. If you're shooting seascapes or somewhere in Antarctica where weather sealing is a major issue, then the fitment of a protective lens filter can be a good idea for peace of mind when you point your lens towards the elements. Make sure that your camera body's up to the task though, otherwise you're still not going to get many photos.

The other point that should be emphasised is that if you are going to buy a filter as protection, buy a decent one, otherwise you're introducing a whole range of optical problems to your photographs, and compromising the performance of the lens you are trying to protect. I don't believe that filters are necessary in the general case, but it's a personal decision in the end. If the filter gives you more confidence to head out to locations with your gear, then fitting one is the obvious answer.

Finally, fit a lens hood. Even if you feel that a UV filter is going to give you some additional protection, it's best to fit a lens hood in addition to the filter. Buy a hood if your lens doesn't come with one. Not only does it give better protection in more circumstances - it also has the potential to enhance, rather than reduce the image quality of your photos.

Happy shooting!