Photo Tips: What Is A Polarising Filter?

[Pugwash]

You'll have read the hint on several photo topics that a polarising filter, or polariser, is the ideal solution to removing reflections. It isn't a magic bullet, as you'll see, but it certainly helps.

Firstly, what is a polariser? It's a filter you screw on to the front of your camera (or your lens, for you SLR people) to polarise light. Yeah, that helps.

Ok, light is a wave, which means it wobbles on an axis. Lots of light wobbles in lots of ways. When you're photographing a watch, what you want to do is eliminate all light wobbling on the same axis as the crystal to reduce the amount of glare it gives. For this, you need a grille that only lets light going in a certain direction through, which is what a polariser does.

To demonstrate, here's a polarising filter. You can see that it's got a white mark that shows the direction of the grille. Rotating the filter changes the axis of the grille, blocking light from the wrong directions.

To show it in action, we need a polarised light source ... and luckily for me, LCDs are polarised, as any kid wearing sunglasses (cheap polarisers in some cases) using a digital watch or calculator will tell you as rotating the watch made it go darker. Anyway, I have an LCD monitor, so that's perfect. I put some tape across my filter so you could see the axis and rotated it.

link to quicktime movie - 0.4MB

So, that's that. Now you understand what it's doing. Let's see it in action on a watch.

Polariser removed:

Polariser in wrong position:

Polariser rotated to the right position:

As you can see, it's not perfect, but it helps. It's not a magic bullet, but in conjunction with decent lighting practices, reflectors and patience (and just a little bit of Photoshop) you can achieve results that would not be as good without the filter.

One important factor is that, as I said before, Sunglasses are a polariser and inversely, a polariser is going to remove light from your scene, meaning you need more time and stability to make up for the lack of light. See the second hand in the photos above? The polariser sapped enough light to force the camera to stay open longer, causing the blur on the second hand. The shot without the polariser has no blur.

Also, for fun, look at the highlights on the strap. See how they move when you change the polarity?

For more science, try Wikipedia: http://en.wikipedia.org/wiki/Polariser

[lovepanerai]

great write up - as usual :-) thanks Pugwash

[mikellem]

Excellent as usual Pugs!

Thanks...

[Pugwash]

If anyone was having issues with the video clip, I've fixed the mime-type on the webserver so it'll play.

Sorry about the clickable link but I can't embed HTML on here.

[jonthebhoy]

Superb as always Puggy.

JTB