Yonatan |
Circular Poleraizer Hi, I got a Circular Polerizer to my Cannon Rebel G camera. I would like to know : 1. What are the golden rules of using such a filter? 2. In what area (outdoor/indoor/landscape etc...) it is most usefull?
Yonatan
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Jeff S. Kennedy |
1. I don't know of any "golden rules" for polarizers. 2. Polarizers are most effective at 90 degreee angles to the sun. They are also useful to remove glare, thus enhancing color. They will remove reflections from water and glass but not from metalic surfaces. They work under sunny conditions as well as overcast. They make nice neutral density filters to reduce the amount of light hitting your film. To find out if it will be useful under a specific circumstance simply put the filter up to your eye and rotate it. If you see a change and you think it helps then use it.
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John A. Lind |
Yonatan, The key to using a polarizer most effectively is understanding how light is polarized as it reflects off of non-metallic surfaces. Jeff has explained its major application in outdoor landscapes and the optimal angle to the sun for enhancing blue sky. For other uses, such as eliminating reflection and glare from a smooth, flat water or glass surface, a polarizer has its greatest effect at "Brewster's Angle." This is the angle at which all of the light reflected from a flat surface is polarized in one direction, which allows a polarizer to block all of it as you you rotate the polarizer ring to its optimum position. Brewster's Angle depends on the index of refraction for air compared to the index of refraction for the reflective material. Each type of reflective material has its own Brewster's Angle. For glass, it's about 56 degrees (varies some by glass type). For water it's about 53 degrees. Measure this angle from pointed straight at the surface, or perpendicular to it. As you change the angle from Brewster's Angle, the amount of reflected light that's polarized goes down, reducing the effect a polarizer can have. Pointed straight at the surface (perpendicular to it) it's zero and a polarizer will have no effect at all. What does all this mean for using a polarizer? BTW, Jeff gave a great tip about using a polarizer as a neutral density filter. Don't forget that one. Comes in handy if you don't need a ND filter often enough to justify buying one. -- John
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