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June 23, 2012

Polarizing filter in digital photography

CPL filter.jpgAs have been said in article about filters in digital photography last week, polarizing filter is a must have accessory for every photographer. Firstly because it has got usage across all fields of photography and secondly because its effect is very difficult, if not impossible, to reproduce in Photoshop. 

So what is polarizing filter and what it does? I don't want to bore you with complicated physics of light and stuff, so simple explained, polarizing filter is a filter which allows only some rays of light from the spectrum through and the rest reflects out. At the same time, it regulate chaotic rays of light spectrum to much cleaner flow.  For example light reflected from shiny surfaces such as water, glass and metal is polarized and by using polarizing filter, this polarized light will not get through the filter. That is why you can get rid of some reflections using this filter. 

Usage of the polarizing filter

Polarizing filter has I think biggest usage across landscape photographers thanks to its ability to darken sky, increase contrast in clouds and eliminate reflection from foliage which gives you richer green color. But be aware, this only works if you shooting in certain position related to sun. Effect is at its best if you shooting in 90 degree angle from sun, any different angle will decrease the effect, but it is still usable, except if you shooting directly towards sun, or with sun behind your back, where the effect is equal to zero. 

landscape no CPL.jpg landscape with CPL.jpg
Polarizing filter in landscape photography - sun is coming from left side, position was not 90 degrees, but effect is still enhancing. Left - no filter, right - with filter

Polarizing filter is architectural photographer's best friend as well. Photographer will benefit not only from its ability to darken sky and make stand out clouds, but also from eliminating reflections. Using polarizing filter, photographer can control if he wants to have reflection of the building in water, same with windows on the building. For this it is very important to shoot with the polarizing filter, because unlike with dark sky, you won't be able to do this in Photoshop, unless you are a graphic designer and you will paint there a completely new building.

building with reflection.jpg building no reflection.jpg
Left - no polarizing filter used, building with its shiny surfaces makes reflections, right - those reflections eliminated by polarizing filter. 

Polarizing filter can be used in product, portrait or fashion photography as well. In fashion and portrait especially if you shoot outside, where your background can benefit from "landscape effects" of polarizing filter. If you'd like to shoot products, polarizing filter will help you to get rid of some nasty reflections and make picture cleaner.

bentley with CPL.jpg RR with CPL.jpg
Details of the cars shoot with circular polarizing filter to get rid of distracting reflections.

For Black and white shooters, circular polarizing filter will make good foundation to your later conversion from color RAW to black and white final picture. After conversion to B&W, pictures thank to polarizing filter has more dramatic, little bit infrared look, especially sky. If you like converting your pictures to black and white and you've never tried polarizing filter, it is about the time for you to start, it may takes you to another level.

Broadway tower CPL colour.jpg Broadway tower CPL BW.jpg
Image shot with polarizing filter is quite dramatic in color, but black and white conversion took it even further.

Polarizing filter and Photoshop

Some say you are not able to simulate effect of polarizing filter in Photoshop. I'd say it is not completely truth, because some effects you can simulate to certain extend. With clever plugin it is not even that difficult and time consuming. But it is fair to say it will never be as good as filter shot. See examples bellow.

example no filter.jpg example CPL in Photoshop.jpg example CPL.jpg
Left - image without any filter, center - left image with Photoshop simulated polarizing filter effect, right - image shot with actual polarizing filter. You can see the difference.

Although the effect above can be more or less simulated, you will not get rid of the reflections in Photoshop. At least not in easy and painless way.

polarizing simulation.JPG polarizing simulation1.JPG
Here are pictures I've used at the top of the article, now I've tried simulate polarizing filter in Photoshop. As you can see, left picture was shot without polarizing filter and Photoshop polarizing filter has no effect at all, if you forget about darker sky. Right picture was shot with polarizing filter, again, no change with Photoshop polarizing effect.

What filter should I buy?

For this question there is a very simple answer, which is as well universal answer to all gear-related questions. Buy the best one your wallet, or wife lets you to buy. You get what you pay for, it is simple as that and there is no point to spent thousands on camera and lens and then ruin it with cheap filter. At the top of the game, there are B+W and Hoya, bit cheaper is Kenko, which is basically made by Hoya, but it comes in different pack. Always look for Multicoated filters, which will do the trick you want, but they won't mess with color balance. Also consider on which lens you will use the filter. If it'll be wide angle lens, you should look for the thin filters to avoid vignetting in the corners of the picture. Thin filters are in general more expensive, but if you have wide angle and tele-zoom with same diameter, you can use one thin filter on both lenses. Also if you'll combine filters, two thin filters are as thick as one thick filter, so consider that as well.

Next time ND filters.

 

Posted by pkuzmin at June 23, 2012 12:35 PM

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