I still have a circular polarizer that I used to shoot with my film SLR, but I just bought a digital SLR and someone told me that digital SLRs need a special circular polarizer... The optics in a film or digital SLR camera are virtually identical so there is no such thing as a "digital camera circular polarizer"
There are linear polarizers and circular polarizers. Older fully manual SLR cameras used linear polarizers. Because of the optics used in autofocus SLR's (almost anyone made in the last 25 years) a linear polarizer will create strange intensity patterns over the image. A circular polarizer is simply a linear polarizer followed by what is called a "quarter waveplate". The linear polarizer is what actually creates the polarization effect in the image (reduced reflections from water, pavement, or windows, darkened skys, etc). The quarter waveplate converts the linear polarized light into circularlly polarized light, which effectively looks like unpolarized light within the camera optics so the polarizing effects within the camera body optics do not affect the image.
The comment about the circular polarizer not requiring adjustment after manual lens focusing doesn't make sense. The orientation of the circular polarizer (because it still acts on the incoming light like a linear polarizer) has to be oriented to a specific angle relative to the scene. If the end of the lens rotates due to the focusing mechanism, (most don't), then the polarizer angle would have to be adjusted after the focusing operation. Digital SLR's do not need a special circular polarizer. The same ones that work for film will work for digital. The "circular" polarizer is convenient because it does not have to be rotated further after you achieve focus, making it the better choice for an auto-focus lens - whether film or digital. Maybe that someone knew about those special polarizers that you need for most digital cameras (since most of them autofocus), but didn't realize that "just" being a circular polarizer is special enough. |
