Some of the light coming from the sky is polarized (bees use this phenomenon for navigation[2]). The electrons in the air molecules cause a scattering of sunlight in all directions. This explains why the sky is not dark during the day. But when looked at from the sides, the light emitted from a specific electron is totally polarized.[3] Hence, a picture taken in a direction at 90 degrees from the sun can take advantage of this polarization. Actually, the effect is visible in a band of 15° to 30° measured from the optimal direction.
Use of a polarizing filter, in the correct direction, will filter out the polarized component of skylight, darkening the sky; the landscape below it, and clouds, will be less affected, giving a photograph with a darker and more dramatic sky, and emphasizing the clouds.[4] Perpendicularly incident light waves tend to reduce clarity and saturation of certain colors, which increases haziness. The polarizing lens effectively absorbs these light waves, rendering outdoor scenes crisper with deeper color tones in subject matter such as blue skies, bodies of water and foliage.[5]
Much light is differentiated by polarization, e.g. light passing through crystals like sunstones (calcite) or water droplets producing rainbows. The polarization of the rainbow is caused by the internal reflection. The rays strike the back surface of the drop close to the Brewster angle.[6]
Polarizing filters can be rotated to maximise or minimise admission of polarised light. They are mounted in a rotating collar for this purpose; one need not screw or unscrew the filter to adjust the effect. Rotating the polarizing filter will make rainbows, reflections, and other polarized light stand out or nearly disappear depending on how much of the light is polarized and the angle of polarization.
The benefits of polarizing filters are the same in digital or film photography. While software post-processing can simulate many other types of filter, a photograph does not record the light polarization, so the effects of controlling polarization at the time of exposure cannot be replicated in software.
Ultraviolet (UV) filters are optical filters which can be used to filter light in the ultraviolet part of the spectrum. These filters reduce haziness that can be created by the presence of ultraviolet light. UV filters appear clear and neutral to the naked eye, and can be left on for nearly all applications. They are commonly used for reflection, transmission, absorption, and blocking UV light or wavelengths, which they do without affecting light within the visible region.
Ultraviolet (UV) filters are optical filters which can be used to filter light in the ultraviolet part of the spectrum. These filters reduce haziness that can be created by the presence of ultraviolet light. UV filters appear clear and neutral to the naked eye, and can be left on for nearly all applications. They are commonly used for reflection, transmission, absorption, and blocking UV light or wavelengths, which they do without affecting light within the visible region.
00Ultraviolet (UV) filters are optical filters which can be used to filter light in the ultraviolet part of the spectrum. These filters reduce haziness that can be created by the presence of ultraviolet light. UV filters appear clear and neutral to the naked eye, and can be left on for nearly all applications. They are commonly used for reflection, transmission, absorption, and blocking UV light or wavelengths, which they do without affecting light within the visible region.
Demonstration of the effect of a neutral-density filter. Note that the photograph was exposed for the view through the filter, and thus the remainder of the scene is overexposed. If the exposure had instead been set for the unfiltered background, it would appear properly exposed while the view through the filter would be dark.
Set of ND filters.
In photography and optics, a neutral-density filter, or ND filter, is a filter that reduces or modifies the intensity of all wavelengths, or colors, of light equally, giving no changes in hue of color rendition. It can be a colorless (clear) or grey filter. The purpose of a standard photographic neutral-density filter is to reduce the amount of light entering the lens. Doing so allows the photographer to select combinations of aperture, exposure time and sensor sensitivity that would otherwise produce overexposed pictures. This is done to achieve effects such as a shallower depth of field or motion blur of a subject in a wider range of situations and atmospheric conditions.
For example, one might wish to photograph a waterfall at a slow shutter speed to create a deliberate motion-blur effect. The photographer might determine that to obtain the desired effect, a shutter speed of ten seconds was needed. On a very bright day, there might be so much light that even at minimal film speed and a minimal aperture, the ten-second shutter speed would let in too much light, and the photo would be overexposed. In this situation, applying an appropriate neutral-density filter is the equivalent of stopping down one or more additional stops, allowing the slower shutter speed and the desired motion-blur effect.
