Red Filters (and other colors)

The other day I wrote about Black and White photography (Black & White) and the very next day, I got an email about the red filters. It seems that they are some of the least understood filters now a days. Instagram users apply the red filter at times to improve their selfies (a term which I fail to understand). I am talking here of the true red glass that fits over the lens. They are also denoted by the Wratten numbers from 23A to 29.

What are these red filter and how are they used? First let me clarify a few things. Instead of calling them red filter, they should ideally be called blue/green-inhibiting or blue/green-subtraction filter. That is exactly what they do.

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Polarizing Filters

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

(Polarizers in different sizes and thicknesses)

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To use a clear filter or not?

One of the heated debates in photography is about the use of clear filters (UV/Haze/Clear) for protection.

The photographers discouraging use of the filters give arguments about the ineffectiveness in providing real protection to lens in case of fall, adding a piece of glass in front of an expensive lens bringing down the quality of the whole setup, increased flares and halos. Hoods provide better protection. There are incidents where the lens with a filter fell down and the filter failed to provide any protection and in a few instances ended up scratching the front element.

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