Polarized filter

BigDaddyCan

worth picking one of these up? I've noticed a lot recently that I have been getting a little bit too much lens flare in some of my shots, I'm using a Canon 500d with the kit lens and a UV filter!

.Longshanks.

In my experience a Polarized filter wont do anything about the flare, it might even make it worse. You would probably be better looking for a lens hood

BigDaddyCan

I assumed it would help the issue! what exactly would a Polarized filter do?

.Longshanks.

BigDaddyCan wrote: »

I assumed it would help the issue! what exactly would a Polarized filter do?

It makes blue skies even blue'r and kills reflections in shinny surfaces.
But the proper answer via google http://en.wikipedia.org/wiki/Circular_polarizer#Circular_Polarizers

BigDaddyCan

nice one!

would it be a common thing to use one?

5uspect

For landscapes, yes.

A circular polariser, as the name suggests, polarises light. Ambient light has random phase angles and when it bounces off a surface like water or glass and into your camera it becomes a bit less random.

Adding a CPL into the mix removes more randomness from the light and only lets through light at a certain phase angle. By rotating the filter you select which phase you let through.

So if you are taking a photo of still water the reflected light from the surface is already quite well filtered by bouncing off the surface. The ambient light coming from above and below the surface is still pretty random. When you adjust your filter to the sweet spot you will see the reflections effectively disappear. You're now blocking the light bouncing off the surface. Turn the filter 90 degrees and the reflection is back.

If you use two polarisers together and turn one at 90 degrees to the other all light is blocked. This is because the first removes all but one phase angle and the second removes this remaining phase angle. Doubling up two polarisers is a fun way to make a variable ND filter for super long exposures.

With a sky you can achieve a very deep blue by removing sunlight.
Here are a few examples:

FoxT

5uspect, this isnt quite right....

"If you use two polarisers together and turn one at 90 degrees to the other all light is blocked. This is because the first removes all but one phase angle and the second removes this remaining phase angle. Doubling up two polarisers is a fun way to make a variable ND filter for super long exposures."

If you use linear polarisers, this is correct. However, a circular polariser consists of 2 filters in one - the first is a linear polariser, which allows polarised light to pass through, and this is then followed by another filter which converts the linearly polarised light into light that is circularly polarised . The reason for this is that modern AF systems can have trouble dealing with polarised light. With a CPL, you get the same visual effect as a linear, but stacking them in the way you describe will work only if you reverse one of them. Try & see!


- FoxT

5uspect

Oh I know about circular polarisation. I just wanted an illustrative example without adding too much confusion.

Promac

You can get a variable circular ND filter quite cheap these days:


This is £43.99:

http://www.amazon.co.uk/Polaroid-Optics-Variable-Neutral-Density/dp/B004GYXRRE/ref=sr_1_4?s=electronics&ie=UTF8&qid=1303890965&sr=1-4

DaireQuinlan

It can go a wee bit crazy sometimes though. I have a few shots of Dubrovnik taken with a wide angle & polariser that I often use as examples of when not to use a polariser :-)



This is one. Polarisers are problematical with wide-angles because the angle of polarisation varies across the sky, strongest at 90 degrees to the sun, weakest looking directly at or away from the sun. If you have a sufficiently wide angle lens you can get a pretty dramatic gradient across the scene. Sometimes it works, sometimes it doesn't. I think these would have been better off without.




Of course shooting them with Velvia probably didn't help either ...