Camera Filtration: A Starters Guide To Polarizers

Summary: Polarizers come in two varieties: linear and circular. Linear polarizers can affect auto focus and light meters in digital cameras, so digital cinematographers tend to use circular polarizers. Polarizers are used to enhance the sky, remove reflections, or remove glare off of leaves and grass.

Length: 3:59 minutes

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6 replies
  1. Brunoinacio
    Brunoinacio says:

    Hello!

    What did you know about polarize a source of light? (with a mirrors or gel’s)
    Is that cross polarization?

    Thanks

    Reply
    • Ryan E. Walters
      Ryan E. Walters says:

      Polarizing the light source works the same way that it does on the camera. So for example there are gels that you can get to put on windows (made by Rosco: http://www.rosco.com/FTVP/roscoview.cfm ) that polarize the light coming through. Then when you add a polarizer to the lens, you can rotate the polarizer filter on the lens to dial in how much light you want the let through the windows. It is a pretty cool trick / tool to use. But it does take some time to gel the windows.

      Hope that helps. :)

      Reply
      • Brunoinacio
        Brunoinacio says:

        Hi.

        Thanks by your reply!

        I’m trying to understand if polarizing one light (or more) on a multi light setup I’ll be able to control the specular of those light’s without affecting the highlights of the other (non polarized) sources! I saw one setup from a still life photographer and he say’s that he is using that technique, but he didn’t explained how it works, and what it changes!
        I know that a polarizer can reduce the reflect of a forecast sky on water (specular light IMO) so, if I polarize one source I will be able to control de reflect of that source! (I want to create true value colors on reflective objects and after with the non polarized give the shape to the object!

        I didn’t tested that yet because the polarizer gels from rosco are very expensive and I’m not sure if will arrive to what I’m expecting!

        Another question, A circular polarizer is variable, isn’t it? And the linear one’s? A circular lets us control the amount of polarization, correct? And the linear one? (I don’t have a polarizer but If that technique works I’ll need to buy one and the linear is more reliable because the lenses have different sizes of front element a matte box solution will be better!

        Sorry about my english…

        Thanks by your time,
        Bruno

        Reply
        • Ryan E. Walters
          Ryan E. Walters says:

          Your english is fine. :)

          I like your idea on how to polarize different light sources- that would be a creative use of those filters. Let me see if I am understanding you correctly- What you want to do, is to put a polarizer gel on a light source on a light that is falling on a part of your scene, and then use that gel to control how much light is reflected back into the camera so that you can control your highlights?

          If that is the case, then that’s not the best application of polarizer gels. Polarizers affect light rays traveling at specific angles. So as soon as the light bounces off of an object, it is now traveling at a different angle so the gel is no longer having the same effect after the light hits an object. Polarizer gels do decrease the amount of light that falls on an object regardless of how it is orientated. So it is my guess that the difference that this photographer is seeing is the decrease of light falling on the object, rather then the actual properties of the polarizing gel. And in this case, it would be better (more affordable) to just use ND gel on the lights that you want to control highlights from specific lights. (ND Gels just decrease the amount of light without effecting the color)

          Circular VS Linear:

          Both do the same thing- they can both be adjusted to change how much light they block. The biggest difference between the two is what kind of camera you are using. The simplistic answer is: Linear was developed for film cameras, and circular for digital cameras. Linear filters can throw off the autofocus function of digital cameras, and it can throw off the internal meters of some digital camera. Circular polarizers do not effect the autofocus, or the in camera meters. So if you want to buy a filter that will work with all cameras, buy a Circular Polarizer filter. If you want to save some money, and you know you will never use autofocus, and you know you will never use the in camera meters, then you can buy a linear filter.

          Cheers,
          Ryan

          Reply
          • Brunoinacio
            Brunoinacio says:

            Hello!

            My goal with the use of polarized gel’s on lightsources is to kill the specular reflection created by the light sources on shiny objects! For example, a cell phone being lited by a softbox will reflect mainly on the screen that softbox! I can see that softbox because the angle of incidence and the angle of the camera are on a particular angle (usually 90 degrees). So, in my head, lol, I will be able to kill that reflection with the polarized, and get the true color value of the phone given by the same source! In other words, kill the catch lights of some sources that are being reflected by shinny surfaces!
            About that photographer, he is shooting with flash heads and if he want to reduce power, he just need to dimm the generator!

            About the the polarizer filter to the camera, I think I’ll buy the linear one, because video is mainly done with manual focus and I work almost all the time with a 758 cine lightmeter, and if not (doing some need to be fast work), I use the wave form. I don’t have nothing against circular filters, but the front element of my lenses and some others that I’m able to rent have different sizes and the probability of have problems with that is higher because I’ll need to buy a lot of different converters and also because I already had to remove some blocked filters from some clients, and that consumes time and stress!

            Thank you by your time,
            Bruno

          • Ryan E. Walters
            Ryan E. Walters says:

            Ah, now I better understand what your talking about. If you are looking to kill the reflection of a light off of a reflective surface like a cell phone, then you can use a polarizer filter on the camera to mostly remove that reflection. I’ve done that before- which is a nice trick. I haven’t attempted using a polarizing gel on the light in order to do the same thing. It sounds like the photographer you are referencing is having success with that- so it must be possible. My only concern would be that the angle of light changes when it is reflected off of the surface of the phone- so I’d want to address it at the camera level, rather then at the light source.

            It sounds like a linear filter will work just fine for your needs. :)

            Cheers,
            Ryan

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