Filters made to call those things which change the composition of the light passing through them. In addition, a number of these filters is to connect different optical attachments for different lenses, are not, according to essence, filters in the full meaning of this concept. For example, the diffusion nozzles of soft focus, called soft-filters “soft-filter”, various tools for obtaining special effects (radiation filters, prismatic nozzle, nozzle diffraction, supplementary lenses with the purpose of the macro), etc.
From the variety of filters and optical lens attachments are only a small part of them has a very specialized purpose. Most filters are applicable in various types of shooting, but the rest should be used only in accordance with its intended purpose, and to create impressive spectrum of special effects for creative photography.
For the manufacture of filters are generally used the same materials as in the manufacture of lenses of high quality optical glass or optical plastic advanced.
Filters used in photography, have, for the most part, or round, or rectangular shape.
For installation on rectangular camera lens filters apply special fastening system that includes a special holder. Here you can set up to three filters simultaneously, adapter ring for mounting a holder along with filters on various lenses, advanced composite (modular) lens hood, protective covers, etc.
Round filters (like glass and plastic) are fixed in a metal frame, fitted with threaded (or bayonet) for mounting on a camera lens. The size of the connection thread for attachment to the lens filters, and other attachments in a different position, the manufacturers of the lenses of the standard series. The most common thread diameter 46, 49, 52, 55, 58, 62, 67, 72 and 77 mm. However, if the set of lenses with different diameter of thread for light filters, acquire a large number of sets of filters is not recommended – it is very wasteful. For such cases there is a better way – threaded adapter ring “step-up” and “down” type. The first allows you to set the filter together with impressive, than the lens thread diameter and the second smaller diameter filter. The practical importance of this first “step-up” rings. The filter is of larger diameter than necessary for the purpose of application on this lens, will probably cause inconvenience only one kind – the impossibility of application of the “native” blend (whatever the method of its mounting on the lens). For example, having the lenses along with the size of the thread for light filters 52 mm and 62 mm, it is convenient to collect a set of filters and nozzles with thread 62 mm than the lenses along with the 52nd thread to set the filters and nozzles via an adapter ring 62-52 mm.
The use of “down” rings should result in a significantly more pleasant effects of vignetting of the marginal rays of light (particularly oblique), and the result is a darkening of the corners of the frame. Therefore, using a filter with smaller than the lens diameter of the threads should be checked carefully for the absence of vignetting when fully open and closed apertures, especially at the edges of the zoom range (for zoom lenses).
The great value has the similar parameter of the filter, as the light transmission. From the unenlightened filter the reflection coefficient at the border “glass – air” is about 5%. The kind of UV filter having two surface “glass – air”, the light transmittance will be slightly less than – 90%. It’s not terrible, but about 1/3 of the remaining 10% of the light still hits the film or matrix in dispersed form. Particularly noticeable drop of contrast from the scattering of light on the filter when shooting contrast scenes.
Variety of filters
Ultraviolet filter UV (0) is one of the most common and frequently used. The main function of this filter does not pass to the film or sensor invisible ultraviolet light (together with the shorter wavelength of 370-390 nm). In the distance are not all UV radiation of the sunlight reaches the Earth’s surface. The short-wave ultraviolet radiation (wavelength of 290-300 nm), called “hard ultraviolet”, has been delayed surrounding Earth layer ozone, however, the weak ultraviolet radiation having a wavelength of 300-400nm, is delayed to different degrees of atmospheric haze, the density of which depends on the location, as well as on weather and time of day.
Usually the UV filter is colourless, the multiplicity is equal to 1 (in this case, filtering out ultraviolet light, it does not absorb light rays involved in the formation of useful images).
To protect the lens from damage and pollution is the protective filter (marking on the rim “protect” or “neutral/clear”). This filter does not change either the spectral composition or intensity or other characteristics of the light passing through. An important purpose of this filter is to protect the front of your lens from adverse environmental influences, in particular dust, drops of moisture, but also from oily fingerprints as well as items that could damage the delicate surface anti-reflection coating the front of the lens.
As a protective filter is allowed without removing it from the lens, apply a UV filter.
Neutral gray filters (marking on the rim “ND” is an indication of the frequency of the filter or optical density). Neutral density filters do not affect the spectral composition of light through them, weakening the light output. It would seem, what for to weaken the luminous flux, because there are many other ways to reduce the number of light entering the camera is to close more the aperture, or the shutter speed shorter, the exposure with 1/2000 – 1/4000 with so long ago became the norm for Amateur equipment? There is a saying that says that “light is never too much!”. In practice, a professional photographer, often there are situations that only use nd filters allow the desired artistic effect. For example, a survey of current water mass in the short excerpt presents a very undesirable effect – “frozen” short excerpt, it is more like glass than water. With shutter speeds slower than 1/30s, water is already becoming like water, allows you to achieve closing the aperture all the way (down to f/22 – f/32), however, does not fall allowing the value of the lens, and no possibility to apply depth of field with the purpose of arrangement of “emphases” in the image. But exposure of the order of 1 – 2 seconds and longer, in which current liquid becomes similar to a shimmering haze, but without the neutral density filter certainly not to achieve in any way – even in the forest in the morning light so many with the purpose of such images. Other example of the use of nd filters shooting portraits in daylight. In such shots for better extraction of the subject (in order to tear it from the background) used a high-aperture lenses, which when shooting almost never defragment (using aperture f/1.4 – f/2.8) that it is often difficult in addition to the use of neutral filters. Most often for this purpose apply neutral density filters reduce the light output at 2, 4 and 8 point. Like, for special purposes, are neutral gray filters and greater multiplicity, letting just a small proportion of light flux falling on them. They are used for observation and photography of objects with very impressive brightness (for example – the surface of the Sun), also similar to shooting with very long exposures (from tens of seconds up to tens of minutes) for the sake of effect “deserted” at what time in the picture remain only stationary objects.
The propagation of light is a wave process, similar to the surface of a pond from a thrown stone in the water. Only the vibrations of light waves is not restricted to one plane, like in the case with surface water masses, but occur in all directions (perpendicular to the direction of wave propagation). But it is permissible to artificially pile that way, to fluctuations of the data occurred in the same plane. In this case, a sort of light will become known as linear-polarized, and also have some non-natural (unpolarized) light properties.
The most obvious use of a polarizer is to remove (or at least the decrease of the intensity) glare formed by bright non-metallic surfaces, in particular glass cases and Windows, painted or plastic-coated surfaces, the surface of the water. Use a polarizing filter is very simple – after all, they produced obvious effects on the eyes and well visible in the viewfinder of the camera. The only thing that is desirable to explore from theory is the fact that the degree of polarization of reflected light varies with the angle of incidence (reflection) of light. So in order to using a polarizing filter completely eliminate the unwanted reflection from the bright surface, you can select shooting parameters so that the reflecting surface (glare with which it is supposed to clean) was located almost at the optimum angle to the camera.
The multiplicity of a polarizing filter is an average of 3 to 4, in this case, there is the use of a polarizing filter requires an increase in exposure by 1.5 – 2 stops (3 – 4 times) in comparison with exposure in addition to the filter.
Polarizing filters have two types: circular and linear. The system circular polarizing filter in addition to protective glass plates and plates of Polaroid, is still the album of the “1/4 wavelength”, which converts linearly polarized light into circularly polarized, which is not attenuated upon further passage through the optical part of the camera, having the properties of a linear polarizer.
The polarizing filter is applied one by one or in pairs, using a neutral filter with variable density. Rotating one filter relative to another, it is possible to change the transmittance of such pairs in a wide range from low of 3 to 4 degrees until almost opaque state at what time the plane of polarization filters are perpendicular, and the light is attenuated more than the 12-15 degrees. Using such combination, we must not forget that now a prominent polarizing filter has to be linear, but close to the camera (in the case of an autofocus apparatus) – circular.