Filter Photography.com

• Clear Filters
• UV Cut Filters
• Polarizing Filters
• Neutral Density Filters
• Graduated Neutral Density
• Black and White Filters

• Cross Screen (Star)
• Diffusion (Softening)
• Transparent diffusion
• *Diopters and split diopters
• Software "Filters"

In the realm of digital photography, camera filters have seemingly gone the way of the dodo. Now light temperature can be altered with in-camera white balance settings and in post-production. For b&w shooters, the yellow, orange, and red filters commonly used in film cameras are no longer needed as many digital photographers now shoot in color and then use photo editing software to convert their photos to b&w to emphasize tones any way they wish. Even the staple grad filter is often cast aside by digital shooters who now prefer to blend multiple shadow and highlight exposures of the same scene into one photo using programs such as Adobe’s Photoshop CS line of software. So why do we still need camera filters?

Clear filters, are completely transparent, and (ideally) perform no filtering of incoming light at all. These are technically not true filters and are purely used to protect the front of your lens from being scratched or smudged.

UV filters are used to reduce haziness created by ultraviolet light. A UV filter is mostly transparent to visible light, and can be left on the lens for nearly all shots. UV filters are often used for lens protection, much like clear filters. A strong UV filter, such as a Haze-2A or UV17, cuts off some visible light in the violet part of the spectrum, and so has a pale yellow color; these strong filters are more effective at cutting haze, and can reduce purple fringing in digital cameras. Strong UV filters are also sometimes used for warming color photos taken in shade with daylight-type film.

While in certain cases (such as harsh environments) a protection filter may be necessary, there are also downsides to this practice as well.

For:

• If the lens is dropped, the filter may well suffer scratches or breakage instead of the front lens element.
• One can clean the filter frequently without having to worry about damaging the lens coatings; a filter scratched by cleaning is much less expensive to replace than a lens.

Against:

• Adding another element degrades image quality due to aberration and flare.
• It may reduce the use of lens hoods, since threading a lens hood on top of the clear filter might cause vignetting on some lenses, and since not all clear filters would even have threads allowing a hood to be attached.

Additionally, users of UV filters must be careful about the quality of such filters. There is a wide variance in the performance of these filters with respect to their ability to block UV light. Also in lower quality filters, problems with autofocus and image degradation have been noted.

A polarizing filter, used both in color and black and white photography, can be used to darken overly light skies. Because the clouds are relatively unchanged, the contrast between the clouds and the sky is increased. Atmospheric haze and reflected sunlight are also reduced, and in color photographs overall color saturation is increased. Polarizers are often used to deal with situations involving reflections, such as those involving water or glass, including pictures taken through glass windows (this uses the phenomenon of Brewster's angle).

Polarizers are the type of filter whose use is least affected by digital photography; while effects that may visually resemble the results of a polarizing filter can be simulated with software post-processing, many of the optical properties of polarization control at the time of capture simply cannot be replicated, particularly those involving reflections. The effects of a polarizer on the sky in a color photograph. The picture on the right has the filter. The effects of a polarizer on the sky in a color photograph. The picture on the right has the filter. In the first picture, the polarizer is rotated to minimise the effect, and in the second it is rotated 90° to maximise the effect - almost all reflected sunlight is eliminated. In the first picture, the polarizer is rotated to minimise the effect, and in the second it is rotated 90° to maximise the effect - almost all reflected sunlight is eliminated.

There are two types of polarizing filters. A linear polarizer filter transmits one of two states of linearly polarized light. A circular polarizer (sometimes called a CPL filter) similarly selects a linear state but then converts it to circularly polarized light, by adding a birefringent layer (typically a quarter-wave plate) to the filter after the linear polarizer. The metering and auto-focus sensors in certain cameras, including virtually all SLRs, will not work properly with linear polarizers, both because of the mirror and because of the beam-splitters used to split off the light for focusing and metering. Circular polarizers will work with all types of cameras.

A Neutral Density (ND) filter creates a reduction in light that is neutral and equal for the film or sensor area. This filter is often used to allow for longer exposure times whenever a longer exposure would normally create over exposure in the camera.

A Graduated Neutral Density (GND) filter is a neutral density filter that varies the effect with a gradient so it can be used to compress dynamic range across the entire scene. This can be beneficial when the difference between highlights and shadows of a scene are too great to allow for proper exposure for both.

A Graduated Neutral Density (GND) filter is a neutral density filter that varies the effect with a gradient so it can be used to compress dynamic range across the entire scene. This can be beneficial when the difference between highlights and shadows of a scene are too great to allow for proper exposure for both.

Black and White Filters are commonly used in black and white photography to manipulate contrast. For example a yellow filter will enhance the contrast between clouds and sky by darkening the latter. Orange and red filters will have a stronger effect. A deep green filter will darken the sky too but will lighten green foliage and will make it stand out against the sky. Also see diffusion filters, which are used to reduce contrast.

• Red filter: Harsh reproduction, intense color deviation, strong cloud formation, good rendering of distance, even with haze.
• Orange filter: Similar effect as red filter, but not such harsh contrast and fewer color deviation effects.
• Yellow filter: Functions without color deviation.
• Green filter: Best for landscapes with a lot of forest and meadows. Creates a contrast between different shades of green.
• Blue filter: Intenifies haze, reduces contrast, produces a mist effect, obscures the distance.

A cross screen filter, also known as a star filter, creates a star pattern, in which lines radiate outward from bright objects. The star pattern is generated by a very fine diffraction grating embedded in the filter, or sometimes by the use of prisms in the filter. The number of stars varies by the construction of the filter, as does the number of points each star has.

A diffusion filter (also called a softening filter) softens subjects and generates a dreamy haze (see photon diffusion). This is most often used for portraits. However, this also has the effect of reducing contrast, and the filters are designed, labeled, sold, and used for that purpose too. There are many ways of accomplishing this effect, and thus filters from different manufacturers vary significantly. The two primary approaches are to use some form of grid or netting in the filter, or to use something which is transparent but not optically sharp.

Both effects can be achieved in software, which can provide a very precise degree of control of the level of effect, however the "look" may be noticeably different. Additionally, if there is too much contrast in a scene, the dynamic range of the digital image sensor or film may be exceeded, which post-processing cannot compensate for, so contrast reduction at the time of image capture may be called for.

The Softar diffusion filter manufactured by Zeiss is widely noted to be made of many tiny globs of acrylic deposited on one surface which act as microlenses to diffuse the light. In some versions the globs are on the inside of the filter (facing the photographer) while on others they face outwards (towards the subject). In various versions the globs vary in number and diameter, from approximately 97 to 150 globs each 1 mm to 3 mm wide.

Homebrew approaches to transparent diffusion filters are generally based on modifying a clear or UV filter by placing various materials on it; the most popular choices are petroleum jelly, optical cement, and nail polish. Transparent filters are more commonly used for the "dreamy" or "misty" effect than for contrast reduction.

Diopters and Split Diopters are simple single or two-element lenses used to assist in close-up and macro photography. They provide some number of positive optical diopters, which magnify the subject and allow objects very close to the lens to be brought into focus. They are sometimes sold singly, and sometimes sold in kits of +1, +2, and +4 diopters, which allows them to be combined to produce a range from +1 to +7.

A split diopter is a diopter in which only half of the camera's lens area is covered by the filter. A round split diopter has a usual filter ring, but is filled with only a semicircle of glass (or plastic). This allows the photographer to photograph an object which is very close against a background much further away, effectively extending depth of field. Careful composition is required to make effective use of this device.

The digital age of photography has also given birth to digital, or post-production filters that you may apply to your digital photo files once they have been imported onto your computer. These include digital versions of many of the filers above and hundreds upon hundreds of additional filter effects ranging from subtle lighting effects to outrageous artistic stylings and abstract algorithms.

While the range of digital filters far outnumbers that of their traditional brethren you should keep in mind that none of these filters will allow you to recapture permanent loss of highlight or shadow detail that a traditional filter may help to avoid. (One the picture is taken digital filters can only manipulate data that the camera has captured.)