Linear polarizer on a DSLR?

Discussion in 'Casual Photo Conversations' started by peter_langfelder, Nov 15, 2009.

  1. My understanding is that linear polarizers are more effective than circular ones, but the optics (prism, meter, AF system) of a modern (D)SLR means the metering and AF may not work and even the viewfinder may go dark, so a linear polarizer is not practical. However, does live view (or, for landscapes, using manual focus and taking test pictures until the histogram looks right) change this equation? Anyone tried it? Thanks in advance for all answers.
     
  2. My understanding is that linear polarizers are more effective than circular ones​
    That's not really true. A circular polarizer IS a linear polarizer, but with a 1/4 wave plate following it. The 1/4 wave plate should not lower polarization efficiency.
    Circular or linear should have no affect on contrast detection AF (which is slow), but phase detection AF still uses the usual optical path and so may be sensitive to polarization. It depends if there is any birefringence in the AF optics. I'm not sure how metering is done in Live view, but if the reflex mirror is out of the metering path (which I presume it is) and metering is done directly off the sensor, then it shouldn't be polarization sensitive.
     
  3. In 1669 a Dutch physician, Erasmus Bartholinus (1625 – 1698) reported a double image is seen when looking through Iceland Spar a crystal mineral, a form of calcium carbonate. In 1808 a French engineer Etienne Louis Malus (1775 – 1812) experimented with Iceland Spar, peered at the sun and saw a double image. When examining a spot of sunlight reflected from a glass window, he saw only a single image. He concluded that light must have poles + and – as in electricity. He reasoned that the window reflection consisted of only one pole. He called reflected light polarized light.
    Edwin Herrbet Land (American 1909 – 1991) scientist concluded that large crystals were unnecessary and proceeded to make, in 1932, filters using very tiny crystals oriented in the same direction embedded in a sheet of flexible plastic. In 1948 he marketed his instant camera.
    Polarizing filters work because light from the sun is un-polarized meaning the light waves vibrate in any and all directions. As the light passes through the atmosphere the direction vibration is altered. This vibration orientation is also changed when light sticks certain objects. The polarizing filter works by selectively allowing light waves that vibrate in only one direction to pass into the camera. The photographer is required to fine tune the effect of the filter by rotating it for best effect. The net effect is the polarizing filter darkens clear skies causing white clouds to stand out. Additionally, the polarizer can subdue reflections from glass – water – and non-conductive surfaces. The polarizer also acts as a UV haze cutting filter. The bad news is, it cuts light transmission by 2 full f/stops.
    The best effects are effects are realized when the sun angle relative to the camera is 90°. The polarizer is also a great help when doing copy work, it can help minimize reflections. This time the best effect occurs when the copy is illumined using lights set 33º to the horizontal.
    Two types of polarizer screens are sold. Both function alike to reduce reflection thus they increase saturation. Circular polarizers are the preferred type for the digital camera. The Circular is made by sandwiching two filters together. One layer is a standard linear polarizer, the other layer is a retarder. The retarder is positioned facing the camera. It de-polarizes after the linear layer has done its work. The idea is to minimize interference with auto focus and exposure determination mechanism that might contain a polarizer.
     

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