Photographic filter is an attachment that will allow certain kinds of light to be able to pass through, and able to reduce or block out other unwanted light sources.In short, the term filter really means anything that modifies the incoming light in some way and includes: polarizing screens, multi-image prisms,close-up attachments, soft focus filters, neutral density (ND) filters, graduated ND filters, and color filters for black and white photography. Filters come in two main shapes: round and square.
Filters add color and a certain touch to a photo that complements the individuals style of photo taking. When you are using a black and white film with filters, you can darken or lighten the tone of the subjects color. The color filters that are used can darken the tone of an opposite color and brighten the tone of the color filter that is being used. For an example, a red filter will make the red leafs on an autumn tree look very rich and bright, while on the other hand the sky behind it that was blue, is now almost black.
Neutral density filters reduce the light entering your camera so that a slower shutter speed,or a larger aperture can be used. Graduated ND filters are used to balance out bright skies against darker foreground scenes.
A neat filter is called the star filter. This type of filter in photography is placed on the cameras lenses to create a star look effect form any source of light. This is very popular with television game shows and used for portraits to provide a soft overall diffusion. A split field lenses is really a full lenses but only half of it is close-up, it is great for taking a picture of something close-up at the bottom like a small flower or bug in focus. The top of the lenses is just blank or empty and the camera uses its lenses to background in focus, say the mountain in the distance.