joyride said:
Speaking of the filters throwing off the AF or AE...I noticed last night as I was going through my D50 manual that it says "the D50 cannot be used with linear polarizing filters. Use the C-PL circular polarizing filter instead." Is there anyway to tewll if this will throw off the AE or the AF? I dont use the AF much, so Im not worried if it gets thrown off. However, the AE i cant afford to lose. Unless it is a consitant error. I think I would be able to compensate for it after testing several exposures. Has anyone epreienced this? Is it very minute, or will it be very far off?
Well, if the manual says that, then I would assume it definitely throws off at least one of the two. See below for more detail.
bantor said:
For some reason i doubt it would throw off the AE, logically the camera should just see a darker image and compensate, but i am no perfesional in regards to filters.
This is not necessarily true. The way it works is this. Some cameras use what are called beam-splitters to measure focus and exposure. I'm not sure exactly how beam-splitting works, but essentially it means that the camera itself also polarizes the light coming to its AF/AE sensor. If the lens filter is polarizing light in a direction perpendicular to the direction that the sensor is
*, then the two cancel each other out, and the sensor essentially sees no light coming through, resulting in an inaccurate reading that would generate an overexposed image. On the other hand, if the polarizer were oriented parallel to the sensor's beam splitter, then the proper amount of light would pass through, resulting in a relatively accurate exposure. If the filter is anywhere between parallel and perpendicular, the amount of light getting through will theoretically vary between 0% and 100%. This means that you can't easily predict how much to compensate for if your camera's metering system is thrown off by a linear polarizer.
To the best of my understanding, what circular polarizers do to correct this is they essentially un-polarize (scatter) the light once it has travelled through the polarizing part of the filter, meaning that the beam-splitting sensor will always receive the same amount of light regardless of what angle of polarization the filter makes.
*If you're not familiar with exactly what polarization is, then google will provide you with some good pages for understanding it:
http://www.google.com/search?q=polarization