Photographic Filters
This resource is a general article introducing photographic filter types, their uses, physical characteristics and optical performance. At the end there is a list of resources for further reading and links to the websites of some well known filter manufacturers. You might like to bookmark this page and use it as a central point from where you can find lots of interesting articles about photo filters. Landscape photographers may want to look at my other article on Filters for landscape photography
Introduction
Filters have an important role to play in Photography from a creative photographic standpoint and also for technical reasons. By learning about filters we open up more technical and creative options that can help improve the quality of our images on the spot rather than resorting to making corrections later in an image editor. Filters are used before the lens and not after the lens.
Some technical reasons for using filters are: contrast control, color correction and exposure control. For example when shooting landscapes in hazy weather there is no way that Photoshop tricks can cut through any haze which has already been recorded in the image. There are also creative reasons for using filters in ways that are limited only by your imagination and some special effects filters can produce effects that would be very difficult or impossible to mimic in digital photo editing applications such as Photoshop. For these reasons every serious photographer should know about filter types, what they can do and when to use them
Filters in Digital Photography
Some people say that no filter is the best filter but this a pretty naive assumption. Other people say you don't need to use filters if you are using a digital camera and this is an even more naive assumption. Although digital cameras have inbuilt controls for color correction they still can't overcome the technical problems that can be solved using Ultraviolet, Polarizing, Neutral Density and Gradient filters. Digital Photographers still need the technical benefits of filters but due to the availability of color balance controls on digital cameras there is less need for color correction filters such as those used for warming and cooling the colors in front of the lens
Filters in Film Photography
Color film photographers get full value from filters because film cameras don't have the built in white balance controls that are found on a digital camera. color films each have their own color characteristics and with color film you need to filter the light before it hits the film. If you use filters with color negative film make sure to tell the processing lab not to apply automatic color correction because this will neutralize any filtration effects you have applied. With color slide film you don't need to worry about this and your slides will look just as you expected with your filter effects in tact. With slide film what you see in the viewfinder is what you get on film
Filters for Classic Black and White Film Photography
Black and white filters are used to improve contrast and to separate those tones which are at the same level of brightness but which are of a different color. These colored filters are also used for controlling skies and foliage in landscape photography and skin tones in portrait photography. For boosting skies in landscape photography on classic black and white film the most common filters are Yellow, Orange and Red where Yellow has the most subtle effect and red the strongest
Lens Protection Filters (neutral filters)
Lens surfaces are coated in a special anti reflective coating and this coating can degrade if it is subjected to contaminants and abrasions. For this reason you need to protect your expensive lenses and you can do this with filters, lens hoods and lens caps. Hoods and caps offer some protection against lens flare and physical damage respectively but they don't protect the lens surface completely. This level of protection is best achieved using a round screw in filter
Filters offer a practical solution when protecting the lens surface from contaminants like dust, dirt, scratches and fingerprints. This is why protective lens filters are not just a gimmick and why it makes sense to use a skylight or ultraviolet filter, which is relatively cheap when compared to the cost of a lens, to protect expensive lenses that are used in risky atmospheric conditions. Shooting conditions can be harsh such as when you are using a camera for coastal scenes where there is often a lot of salt water spray and sand in the air; in industrial photography there is dirt and grime and rally photographers need to protect their lenses for obvious reasons.
Ultraviolet (UV) filters can be left on the lens at all times for protection without affecting image quality. These filters are very light yellow in color and they cut through blue haze in the atmosphere. This is due to the fact that UV filters attenuate wavelengths at the violet end of the spectrum. A strong UV filter can cut through that distant blue haze that is often prevalent on sunny days and they can also counteract purple fringing on digital cameras. Skylight (skylight 1B) filters also protect the lens and they also warm up shadow areas under blue skies, making them ideal for outdoor portrait shots and when shooting landscapes high up in mountainous regions
Color Correction Filters
The color temperature of daylight is affected by many variables: time of day; the season and the weather. Color Correction (CC) filters can be used for warming (81 and 85 series) or cooling (82 series) daylight. The 81 and 85 series are orange in color (blocks blue) and the 82 series is blue in color (blocks red).
81 A - very light red in color, good for filtering blue haze at midday
81 B - produces pleasing skin tones in outdoor portrait shots taken with fill in flash
81 C - reduces blue and green and good for reducing haze under strong blue skies
In a photographic sense there is not a lot of value to be gained from using color correction filters on a digital camera. Digital cameras have controls for adjusting white balance and this means that the warming and cooling filters used in color film photography may be irrelevant to most digital photographers. Some digital landscape photographers do use them out of personal preference because the stronger color means they can produce natural looking prints that are more pleasing to the human eye
Exposure Compensating Filters - Neutral Density Filters
Neutral Density (ND) filters attenuate all wavelengths of light entering the lens. This attenuation is very useful for increasing exposure in bright light, allowing you to use slow shutter speeds or a larger lens aperture. In daylight slow shutter speeds enable you to create motion blur on moving subjects like people and flowing water. Wider apertures allow you to create shallow depth of field for creating more striking portraits of people, wildlife and nature. Click the waterfall thumbnail below to see the larger version which clearly illustrates the motion blur effect
Close Up (Dioptric) Filters
Close up filters (supplementary lenses) allow you experiment with macro photography using the standard and short telephoto lenses which are commonly bundled with entry level SLR cameras. For many photographers the cost of a true macro lens is prohibitive but relatively cheap close up filters invite you into this type of photography at low cost. These filters are useful for photographing subjects such as postage stamps, insects and jewellery. Close up filters come in various strenghts and are usually numbered: +1, +2 and +3 where the higher the number the higher the magnification factor
Special Effects Filters
Starburst, Diffusion, Rainbow, Spectrum etc. These filters are more extreme and said by many to be just gimmicks but they can be experimented with and used in many different ways. Diffusion filters can be useful in portrait and nature photography. A centre spot diffusion filter is clear in the centre and becomes more diffuse towards the edges
Filter classification and numbering
Photographic Filters are classified and individually identified by a series of Wratten Numbers which are named after the Englishman who invented this
numbering system. The Wratten number of a filter describes the filter color, filter factor (% of light transmission) and the required exposure
correction factor in F-Stops
view wratten numbers chart
Quality and Performance of Photographic Filters
Using poor quality filters on an excellent lens makes little sense and will stop you from getting the very best quality that your lens can deliver. For any given filter type there will be noticeable differences in optical quality and performance between different brands. Sometimes you will find that an inexpensive filter type from one manufacturer might out-perform a more expensive filter from another manufacturer. Filter manufacturers produce performance charts like that shown below which might be of assistance if you want to know how quality is measured. The theory is useful for academic reasons but in photography everything eventually comes down to trial and error
Materials and Coatings
Photographic Filters are made from glass or from plastics such as Polyester and Polycarbonate. Hi tech anti reflective coating technology is used on the more expensive filters and offer an optical performance that is far superior to the quality obtained from cheaper uncoated filters. For example, an uncoated filter might reflect about 10% of the incident light before the lens whereas a high quality multi-coated filter can reduce the reflectance levels right down to something like 0.5% or even less. Uncoated filters are also notorious for causing reflections inside the lens which can cause flare and a lowering of contrast
The quality of materials use for the mechanical parts of a filter system is also important. High quality brass fittings do not wear our or become jammed in the screw thread on the front of the lens. On round screw in filters the thickness (length) of the filter housing is important because it determines how far the glass is from the lens. If it is too far out then you risk vignetting and other performance problems with wide angled lenses. To address problem filter manufacturers produce slim versions of selected filter types and sell them at a premium price
Filter shapes and sizes
Photographic filters are either round or square. The round filters have a screw thread around the outer edge of the housing so that the filter can be screwed directly on to to front of the lens. Circular screw in filters range approximately from 30mm up to 127 mm in diameter and they can be used on camcorders as well as camera lenses. Square filters require an adaptor which is first screwed onto the lens in the same way as a round filter and then you drop the square filter into a slot on the front of the adaptor. Square filters are more cumbersome and take time to set up properly and for this reason they will not suit all photographers
What size of round filters you need depends on what lenses you have in your collection. The sensible solution is to buy filters to fit the lens with the largest filter thread and use an adaptor for using these filters with other lenses
Cleaning and Storage
A lens cloth is best for cleaning filters. No chemicals should be used but clean water may be fine for removing hard stains. Round screw in filters are stored in round protective plastic cases which screw apart much like contact lens cases while square filters are stored in filter wallets. Some manufacturers sell square filters in sets that come in nice protective wallets. There are different sets available for landscape photography, portrait photography etc
Filter Manufacturers
B+W filters are German made and are the very best on the market. They all have least a single coating and are expensive but you are paying for high quality German engineering. B+W also make the best adapter rings because they are made of Brass and not Aluminium like those made by Hoya - Brass is a more durable material than Aluminium B+W filter handbook
Hoya is a Japanese filter manufacturer and their filters are of excellent quality while being less expensive than B+W filters. Their slogan is 'The Difference is Clear' and they make great products thare in held in high regard by most photographers Visit the Hoya Website
Cokin is a French manufacturer and their filters are uncoated and come in three sizes. Cokin filters are square in shape and require an adapter. product brochures
Lee manufacture resin and polyester filters and are another popular brand name in photo filters Lee website
Tiffen many people say that Tiffen filters are poor for photography but if the television industry uses them then they can't be bad Tiffen website
Nikon filters are reputed to be manufactured by Hoya and they are expensive. You are getting a high quality product that offers excellent optical performance. Their polarizing filters are coated and are reputed produce neutral colors without the color cast produced by other makes of polarizer
Related
References and resources
Neutral Density Filters - wikipedia article on varieties of neutral density filter
Wratten Numbers - a nice table on wikipedia explaining wratten numbers
Polarizing Filter - an amazing interactive little Java appplet which simulates using a polarizing filter. As you drag your mouse you see can the polarizing effect filter simulator
