The UV Filter Debate

The debate about the use of ultra-violet (UV) filters (or not) is one of those issues which polarises (pardon the pun) the photography community.

There have probably been more arguments over use of UV filters than there have been Canon vs. Nikon skirmishes.

My own position on the use of UV filters is well documented and places me very firmly in the ‘against’ camp.  I do not believe UV filters are necessary or beneficial, and I specifically will not use them.

To explain why, I’ll firstly explain why people might buy these filters.  The two main reasons are:

  1. to filter out UV light; and
  2. to protect the lens.

Filtration of UV light might be one reason for the use of such a filter, but in the digital age, and unless you’re shooting at high altitudes, it’s not necessary to use a UV filter, as digital sensors are nowhere near as sensitive to UV light as film.

The second reason concerns ‘protection’, and I use the term very loosely, as I do not believe a UV filter provides effective protection for a lens.

Firstly one must define what sort of protection is desirable.  A person might use a UV filter in a protective capacity to prevent any or all of the following:

  1. dust;
  2. moisture;
  3. fingerprints; and
  4. impact.

Let’s look at each of the above undesirable elements and assess the effectiveness or merit of a UV filter for that form of protection.

1.  Dust

I do not consider dust to be a problem.  It blows off.  In as much as dust can land on a lens’s objective element, it can also land on a filter.  Either way, it’s going to be necessary to remove dust in order to clean the glass.

2.  Moisture

Like dust, water can be removed from a lens’s objective element.  It wipes off.  It doesn’t harm a lens, and when shooting in inclement weather or conditions that would otherwise cause water to contact a lens (eg, sea spray), there is going to be some time spent wiping water off glass.

Some Canon lenses specifically require a filter (the type of filter is not specified) to complete the weather sealing capability of the lens, as the objective element moves as the lens focuses or zooms.  One such example is the Canon EF 16-35mm f/2.8L II USM lens, whose objective element moves as the focal range changes, but this movement is within the lens’s outer barrel; in other words, the lens’s entire structure does not change in length, but the recessed lens does move along the inside of the barrel’s construction.

3.  Fingerprints

Some people might use a filter to avoid getting fingerprints on a lens.  Again, fingerprints can be removed.  Personally, I have never found fingerprints to be an issue; I simply don’t get them on my lenses, and as I’ll discuss later, there are more effective preventative measures.

4.  Impact

This is the clincher.  Many people buy UV filters in the belief that it will protect their lenses from impact.  What sort of impact?

The scenarios can vary widely, but let’s look at an extreme example.

Firstly, there’s the dreaded lens drop.  People drop lenses.  I’ve done so myself.  A UV filter offers absolutely no protection whatsoever from an accidental drop.  Simple physics explains why.

In most cases, the objective element is recessed into the front of the lens, ironically due to the need to provide a rim for the mounting of screw-in filters.  With the exception of a few lenses (ultra-wide rectilinear lenses and fish-eye lenses), the objective element does not protrude beyond the rim.  In the case of ultra-wide rectilinear lenses and fish-eye lenses, these protruding elements are protected by an in-built, non-removable lens hood.

In the unlikely event that a lens were to hit the ground face-first, it would be even more unlikely for the objective element to strike the ground or an object on the ground.  In terms of probability, it is more likely that some part of the lens barrel will strike the ground, owing to the fact that there is far more surface area comprised of the barrel.

Now, in the rather unfortunate event that a lens did strike the ground or something on the ground at such an angle for the objective element to make direct, blunt-force contact, what would a thin sheet of glass to do protect it?  Absolutely nothing.

The filter would smash, and the lens it was intended to protect would still bear direct impact.  Furthermore, the shards of glass from a shattered filter would quite possibly scratch the fine coatings on the objective element.  That’s not a situation I consider acceptable or sensible.

It is also to be remembered that the objective element of a lens is far thicker and far tougher than the glass in any filter.  It would take significant force to crack an objective element.

As I mentioned above, I have dropped a lens.  A few years ago I dropped a reasonably heavy lens from waist height onto bitumen.  Now, the lens was wearing both its front and rear caps, but the damage the entire unit sustained was very low, and surprisingly so.

The part of the lens that actually hit the ground (after which it bounced and rolled away) was the side of the barrel, towards the front.  There was a minor dent to the exterior of the barrel.  The fact that the lens was wearing its caps made no difference, but I’d prefer caps on than caps off.

Naturally there was no UV filter on the lens.  Had a filter been present, the shock force of the impact would likely have shattered the filter and left shards of glass in direct contact with my lens’s objective element.

One last issue to consider with the use of a filter in this scenario is that if the rim of the filter strikes the ground, it will almost certainly be deformed, and may be impossible to remove, as the impact can compress the metal of either the filter’s rim or the lens’s filter threads, thus permanently damaging them.

Impact can also take the form of less-brutal contact with glass, such as a tree branch or some other object still coming into contact with the lens, but not with the velocity of a drop or a flying stone thrown up by a passing vehicle.  My belief, as I will explain further in this article, is that hoods offer more effective protection.

The Negative Effects of Filters

While the use of a UV filter can demonstrably be shown to be useless at best, or ineffective at worst for protection, there are also some negative consequences that arise as a result of using filters: image quality degradation.

Image quality degradation is more often the result of using cheap, non-coated UV filters, but I have seen first-hand image degradation when the filter was a Hoya HMC (Hoya Multi-Coated) filter, so even the better filters can still produce undesirable results.

The first negative side-effect is a loss of contrast and sharpness.  There are examples on the Internet showing the same scene captured with and without a filter, and a visible loss of clarity is apparent in the image captured with the filter attached.

The other issue is flare and ghosting when shooting at point sources of light.  This problem is likely to be encountered at night when shooting streetscapes and cityscapes, which often feature bright sources of light (eg, street lights or building lights) in the darkness.

This is what happens:

Light from the distance point source enters the lens.  The light reflects off the lens and falls upon the inner surface of the UV filter, from which it in turn reflects back into the lens.  The result is ghosting and flare.  Utterly undesirable.

Multi-coated filters generally reduce this, but as I mentioned, I have seen it occur even with a multi-coated filter.  In January of 2010 I took a friend from Queensland to shoot the Sydney Harbour Bridge and Sydney Opera House from Mrs Macquarie’s Chair, and while we were there, another photographer was also shooting night scenes.  Her images weren’t turning out well, and when we removed the filter and she took the same photo again, the image quality visibly improved.

Based on that first-hand experience, I would not endorse the use of any UV filter when doing night photography in locations where there are point sources of light.

My Approach

I stated early in this article that I do not use UV filters.  I believe they do not offer adequate protection, and have seen that they can degrade image quality.  I do not consider either situation acceptable.

What I instead advocate and practice is the use of lens hoods when shooting, and lens caps when not shooting.  These provide far more protection than any filter.

Lens hoods do three things:

  1. reduce stray light hitting the lens at oblique angles and thus causing flare;
  2. increase contrast as a result of keeping angular ambient light out; and
  3. keep the objective element well away from hands and other foreign objects.

If a lens is dropped, the hood or barrel (as described earlier) will be more likely to take the hit.  In most cases, lens hoods are made from plastic, so they will flex when they come into contact with a hard surface at significant velocity.  This cushioning, much like a car’s shock absorber, absorbs the force of the impact far more effectively than the rigid surface of a filter rim or the lens barrel itself.

Lens caps are simply essential to protect the front and rear elements of a lens when it is not in use.  Dust, moisture, fingerprints and blunt-force impact are all kept well out of harm’s way when caps are attached.

It would be remiss of me to neglect mentioning Hoya’s HD (high-density) line of filters.  These have up to four times the breaking strength of a normal filter.  Videos on YouTube show people deliberately slamming these into the corner of benches to demonstrate the strength of the glass.

While I have not seen these filters, they certainly have more merit than a regular UV filter for impact protection purposes, but I still believe that direct impact to the objective element of lens resulting from a drop would have velocity which exceeds the strength of the HD filter’s glass.  I’d trust my hoods before I’d trust a filter.

So, hopefully this article provides some insight into what UV filters can and cannot do — mostly what they cannot do — and also explains my philosophy behind refusing to use these filters on my lenses.

In parting, the advice I would offer to anyone who would still use a filter is this:

  1. buy the highest quality filters available;
  2. remove the filters when shooting night scenes with point sources of light;
  3. do not rely on these alone as protective devices; and
  4. use lens hoods and lens caps.
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