Most fil­ters (in front of lenses) that people try to sell you don’t make sense in digital pho­to­graphy. In par­tic­u­lar UV fil­ters, sky light fil­ters or pro­tect­ive fil­ters — the first two are irrel­ev­ant, and you usu­ally pro­tect your lens much bet­ter by using a lens hood. All that these “use­less” fil­ters do is degrade image qual­ity.

The only two fil­ters that make sense, I guess, are polar­isers and neut­ral dens­ity (or just “grey-​”) fil­ters. I might talk about the lat­ter at some other time, today’s topic is the polar­iser. If you don’t have one, get one. Unfor­tu­nately, the bet­ter ones (that’s the ones you want to buy, since they have decent coat­ings on them, are more col­our neut­ral and usu­ally live longer) can be quite pricey, espe­cially when you have large lens dia­met­ers.

Why? Well, the main effect of these fil­ters is one that you just can’t repro­duce prop­erly in post-​processing: They reduce reflec­tions. There are mainly two situ­ations where this is import­ant 1) in the sky and 2) on col­our­ful objects (well, actu­ally 3) on trans­lu­cent sur­faces). In the sky the fil­ter gives you much deeper blues as it removes some of the sun­light reflec­ted off the haze in the air (which leaves the deep blue rather “milky”). On objects, such as grass, leaves, build­ings, etc. it reduces the reflec­tion of the ambi­ent light to again just give you the actual sig­ni­fic­antly more sat­ur­ated col­our of the object. Third, it allows you to shoot through win­dows or water sur­faces to reveal what’s behind (again, by can­cel­ling out reflec­tions of the sur­round­ing).

Sounds great, doens’t it? Well, there’s a catch or two. On the one hand, you lose about 1 to 3 stops of bright­ness. On the other, in order to be able to can­cel reflec­tions, you need to get the angles right (this has to do with the phys­ics behind all this). Since the post is already long enough, I won’t go into explain­ing how exactly to use them — if you’re inter­ested you can have a look at this art­icle for instance, or this page.

As for the photo above — you guessed right, it’s been shot using a polar­ising fil­ter. No post-​processing really, just the filter’s magic :-)