A dark ND filter is a necessity for long exposure times when the ambient light is very high. After reading various reviews and collecting feedback from photographer friends of mine, I bought a Hoya PRO ND 1000x filter. I could not get it on time for a recent trip that I had made but I still managed to use it for some test photographs.
Polarizing Filters or simply Polarizers were second most used filters in the film era, first being the UV filters. Polarizers work on the principle of letting only one plane of light waves to pass through. Remaining planes of light waves are blocked. Earlier polarizers had a single polarizing layer. Then came the autofocus cameras. There were times when the angle of polarized light being let into the lens would not coincide with the autofocus sensors and autofocus used to fail. Circular polarizers were introduced. These had another plate after the polarizing layer to rotate the light. This reduced the problems with the auto-focus systems. Due to their construction method, the circular polarizers show the polarizing effect only when seen from ‘thread side’. When seen from the ‘groove side’ polarizing effect is not seen, instead just a color shift is visible.
(Polarizers in different sizes and thicknesses)