Saturday, July 26, 2008

Buying A Polarizing Filter

photographyOne of the benefits of digital photography is that one doesn't need to have a whole kit of lens filters in order to achieve different looks. Most processing can be done in "development" on the computer. But one filter that is still critical for outdoor photography is the polarizing filter. In this article I'll tell you why you need one, link to some further resources, and enter the dark and confusing world of available types, brands and models.

To start with, why would you want to use a polarizing filter? Simply, to increase contrast and get rid of glare, to make your images punchier (higher in contrast) and to improve colour saturation. A polarizer can darken clouds, plus get rid of annoying reflections from glass, water and foliage. The price you pay for all of this is a reduction in the light that reaches the sensor... from 1 to 4 stops depending on the degree of polarization of ambient light.

Yet even this can be a benefit. If you deliberately want to reduce the light getting to your camera, a polarizing filter can work well either on its own, or in concert with a Neutral Density filter. This is a common technique when shooting flowing water. Cutting the light several stops means you can shoot with a slower shutter speed and get that nice smooth water effect. (Of course you'll need a tripod.)

Please note that none of these benefits are easily achievable in post-processing. You need the polarizer on your lens when you shoot. For more read the articles at photo.net and Digital Photography For What It's Worth.

So, which ones to buy? This is definitely a confusing topic because of all the different variations and similar names. Be assured I have tried very few, so most of this information has been culled and collated from other experts.

First, there are two different systems you can use. The first involves a mounting kit into which you can insert one or more square filters. The most popular brand is Cokin, but there are more professional makes like Lee and Hitech. In my opinion these are too fiddly and expensive to bother with unless you have very specific needs. In that case you are likely not reading this article. (I had a Cokin system when I shot film, but in those days combining multiple filters was more commonly useful.)

The second system comprises circular filters which screw directly onto the front of your lens. These are individually cheaper and more commonly available than the above systems. For digital cameras they are recommended.

Next, be aware that there are two basic types of polarizers, linear and circular. (This "circular" is not the same usage as in the previous paragraph. Here it's the polarization effect that's circular; previously it was the shape of the glass itself that was a circle. Got it?) Just get a circular polarizer since it will definitely work with your camera.

A few other factors...

1. You'll want a filter with a front thread or you won't be able to screw a hood on. And you should always shoot with a lens hood.

2. You absolutely need a filter with multi-coating, to prevent flare and ghosting. This can be particularly bad with filters since the gap between the filter and the front lens element provides ample opportunity for unwanted bouncing light.

3. You can either buy a filter in each size your lenses cover, or buy the largest size and get step-up rings. That's way cheaper but more fiddly.

4. Thinner filters may help reduce vignetting at small focal lengths. But on APS-C sensors I haven't read of people having trouble with good makes.

So what are the decent makes? These are generally recognised to be Tiffen, Hoya/Kenko, B+W and Heliopan, in escalating cost order. Eliminating the top and bottom of the scale helps narrow the purchase choice.

The double-threaded Hoya's include the "Hoya HMC" with 3 coating layers at 9mm thickness, the "PRO1 Digital DMC" with 3 layers at 5mm and the "Super HMC PRO1" with 6 layers at 5mm. But avoid the similarly named "Hoya Super HMC".

The B+W offerings have a superior brass mount. The two options here are the "B+W MRC" (not the "B+W MRC Slim"... sigh) and the superior "B+W Kaesemann MRC", which is sealed around the edges to help longevity in extreme climates. Perhaps if I was shooting in the desert or jungle I could justify that. But not here in moderate Ireland.

Following this process, the choice for me came down to the "Super HMC PRO1" or the "B+W MRC". Comparing available prices I bought the latter in 77mm, along with requisite step-up rings. This even though I don't own a 77mm front filter lens. Yet.

Here's something else to look out for. If I stick a 67-77mm step-up ring on my most used lens, and then mount a 77mm filter, how am I going to attach the original lens hood? Well, I'm not, so I spent a couple bucks for a 77mm collapsible rubber hood. Now I can use that anytime I am using the polarizer.

For €100 I snagged the B+W 77mm MRC F-PRO* Circular Polarizer, 52mm to 77mm and 67mm to 77mm step-up rings (metal not plastic), a 77mm collapsible rubber lens hood, a Lens Pen for cleaning and a wallet to hold the rings and filter. That's a reasonable price for a complete kit.

I hope these tips help you get started with these useful filters.

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2 comments:

iordakis said...

Great post, check here everything about polarizing filters http://polarizingfilter.blogspot.com/

robin said...

As a late addendum I should note that cost does not necessarily equate with quality. The very dear Heliopan do not perform as well as cheaper makes in tests. The Lenstip site has scientific tests of many brands that confirm this:
http://www.lenstip.com/115.4-article-Polarizing_filters_test_Results_and_summary.html

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