Morning Kit and Afternoon Sigma!

Started Sep 29, 2013 | Discussions thread
Jeff Peterman
MOD Jeff Peterman Forum Pro • Posts: 12,859
Re: Morning Kit and Afternoon Sigma!

A polarizer can do things that an ND filter can't: selectively darkening reflected light, which can remove glare from glass/water and improve color contrast. If you use TWO polarizer filters you can have the advantages of a polarizing filter and a variable density ND filter: you put a circular polarizer on the lens and a linear one (much cheaper) in front of that: by rotating the filter on the lens you can get the polarizing effect that you want (and a roughly 2 stop ND) and by rotating the filter in front of that you can go to essentially an infinite ND.

The simple way to think of this is that a polarizing filter blocks all the light that has a wave form in a specific direction, so adding another in front and rotating it 90 degrees relative to the first with result in all the light being blocked. A circular polarizer has a plate on the back that randomizes the wave forms so that the light entering the camera is not polarized. But remember I said "a simple way to think of this..." the actual technical details are more complex.

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