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There was a request from a Thursday Tips readers for a piece on filters, so this is the start of an episodic series on the subject.  There’s simply too much for me to say on this topic for a single installment, so I’ll periodically cover a variety of different filters and related issues in future entries.

When I was still shooting with film, I had quite a selection of photographic filters that I hauled around in my gear bag.  After converting to digital capture 8 ½ years ago, I ended up ditching more than half of them.  In this series, I’ll discuss the filters I still use, the ones I’ve discarded and explain the whys behind both groups.

By way of introduction, there are enough different kinds of filters out there to keep glass and resin companies in business for years.  Polarizing filters, color enhancing filters, color subtraction filters, warming filters, cooling filters, neutral density filters (standard and graduated), color filters (mainly for black & white work), protective filters, diffusion filters and probably a number of other classifications that I’ve overlooked are all part of the mix.  What’s more, most of the above categories of filters come in different strengths and different sizes (to fit the different sized front elements on various lenses).  Many filters also come in varied thicknesses; slim filters are specially designed to avoid vignetting on wide angle lenses.  Many come in both screw-on varieties (that literally screw on to the end of your lens) and in forms designed to slide into filter holders that attach to the end of a lens assembly.  Some exotic prime lenses—300 mm/2.8 and up—require what is known as a “drop-in” filter that slips into a socket in the lens assembly.  The whole enterprise can be quite dizzying.

In this installment, I’ll cover protective filters.  What are they and what are the arguments—yea and nay—surrounding them?

A protective filter is basically a clear filter that screws on the end of any lens designed to accept screw-on filters.  They are typically referred to as UV (i.e. ultraviolet), or Skylight filters.  Once upon a time, way back in the film era, a UV filter could be relevant to certain types of emulsions that were highly susceptible to UV rays, but this is effectively irrelevant in the digital era (and frankly was irrelevant in the modern film era as well).  A UV filter on a lens attached to a digital camera is good for one thing—protecting the front element of the lens from damage.  There is scarcely any practical difference between a UV and Skylight filter.

What kind of protection do these kinds of filters provide?  Well, they can protect the front element of your lens from becoming scratched.  And, in a worst case scenario, if your lens (heaven forbid) crashes to the ground, the filter may absorb the brunt of the impact.  I know of several people who swear by protective filters after experiencing near disasters of this sort, losing the filter to breakage in the process but retaining the use of their much more expensive lens, intact.

This sounds like good insurance, doesn’t it?  I mean, why wouldn’t you want a protective filter on all of your lenses all of the time?  Like everything else in photography, there’s a tradeoff.  First and most importantly, any additional piece of glass on the end of your lens has the potential to degrade image quality.  A cheap filter certainly will degrade the quality of your image, so that means getting an expensive, high quality filter.  (By the way, I always recommend a high quality filter if you’re going to use one.  There are fewer things sillier, in my mind, than those photographers who stick a cheap, low quality filter at the end of an expensive, high quality optic.  It’s rather like wearing top-of-the-line undergarments below torn shorts and a t-shirt.  If that sounds elitist, it isn’t; I wear low quality undergarments below my torn shorts and t-shirt.)  Frankly, scratches on a front element typically have less impact on image quality than a low-end filter and the cost of a high end filter is often as much as the price of repairing a lens.  And even a high end filter can negatively impact image quality.  Anything you stick on the end of your lens will, at least minimally, degrade image quality.  This is a maxim worth remembering.

So, in light of the above paragraph, I don’t own any protective filters, right?  Well…actually, I do…but I don’t’ routinely use them.  I have a pair of high end B+W protective filters that I purchased specifically for shooting amidst the salt spray of the seaside or blowing sand on the beach or inland dunes environments.  The images accompanying this entry demonstrate the sorts of places where I would be inclined to use a protective filter.  I don’t want to have to deal with the potential nightmare of saltwater or blowing sand hitting my lens.  But those are the only times I have these filters in place (and, in fact, if it’s not windy I don’t even use them then).

To protect or not to protect with a filter is a fairly active—and surprisingly passionate—argument among photographers.  I’m fairly unusual in that I don’t have especially strong feelings about the subject, but I generally take the attitude that protective filtration isn’t worth the trouble and expense.  Your mileage may vary, but at least consider the pluses or minuses of using protective filters before making a decision either way.

Thursday Tips is written by Kerry Mark Leibowitz, a guest blogger on 1001 Scribbles, and appears every other Thursday.  To read more of his thoughts on photography, please visit his blog:  Lightscapes Nature Photography.