Filters are circular objects, that are screwed onto your camera lens, or square pieces of transparent material which are attached to an adapter and a lens holder. They add certain effects, or abilities, such as increasing contrast, reducing reflections, extra zoom etc.
These days, fewer people use filters, because it is easier, and in the long term, less expensive to add these effects in post production.
UV stands for ultraviolet, it is a type of light wave length we cannot see. The filter reduces haziness, and while digital sensors are not so sensitive to this, they are still used because they offer protection to the lens.
ND neutral density filters allow less light in, and are used for long exposures, often for shooting waterfalls or motion burring clouds, or in overexposed scenes.
Graduated ND Filters are similar to ND filters, but the effect is not the same all over. They darken the sky, while leaving the foreground normal. They are useful, but the gradual transition is straight, while natural horizons are usually not, so they do have limitations. They are always square, so tha the effect can be varied.
Polarizing Filter (Coming soon!)
These reduce the reflections on non metallic surfaces, such as water, or glass. They can be adjusted by rotating the front of the filter. They are useful, but expensive.
Macro Filters, also known as close up filters, or diopters are not ordinary filters, they act like a second lens. With these you can get a macro image, with a telephoto lens. They can be stacked on top of each other for extra effect. WARNING! They reduce quality, making the image softer, and so should be used with caution.
Extension tubes have a similar effect, but dont soften the image as much.
Colour filters are rarely used, they change the colour and contrast slightly, but this is now usually done in post production.
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