Accessories for television lenses

By Lyudmila Berezenceva

Review contents:
Accessories for television lenses Optical accessories and converters from Okno-TV Company Canon Accessories Optical accessories from Cavision Products from Chrosziel Film & Video Optical accessories from Cinema Technologies Optical accessories from Fujinon: a glance in the other dimension Expanded possibilities of DSR-PD170

The optical accessories play the very important role in modern shooting technology, where they are vastly increased the working possibilities of the television cameras under TV-shooting.

Under all variety of zooms, produced by leading television optics manufacturers, the TV and cinema cameramen broadly use the optical devices, allowing to solve the difficult problems (the close-up shooting, extension of the shooting space margins, artistic expressiveness of concert programs, etc).

The main types of optical devices are the following:

• Converters (wide-angle and of long focal length);
• Extensions and auxiliary lens (wide-angle or superwide-angle);
• Extenders;
• Lenses for short-distance shooting;
• Effect filters and light filters.

The optical accessories application in the same shooting conditions can be different and only professionalism of the operator allows to choose the most optimum accessories.

The converters are afocal systems which include 3…5 lenses, installed before TV camera lens. The converters of two types are produced: wide-angle and of long focal length.

The wide-angle converters enlarge the maximum angle of the field of vision of the lens to 20…30%. The broader angle of the field of vision enables to get more information, particularly under shooting in small rooms. Herewith the depth of definition is increased and the minimum distance to object is decreased that allows to the operator to approach to the shooting object without deterioration of the focusing. The converter does not cause the light losses so there is unnecessary to change the endurance or luminosity. Aside from increasing of the angle of the field of vision the advantage of the wide-angle converters is in conservation of the scaling possibility in the range of the focal lengths changing. The factor of the modern wide-angle converter increasing is in the range of 0.65…0.8, and their weight does not exceed 1kg.

TV-converter (of long focal length) is fixed on front surface of the lens, enlarging the range of the maximum focal lengths. The minimum distance of the shooting of the lens in combinations with TV-converter is proportional to square of the factor of picture expansion. The light loss on reflection and absorption in glass does not influence for colour rendering and luminosity level. TV-converter is working only within the range of greater focal lengths (2.2…3.5 m). As a rule, the factor of these devices extension is in the range of 1.5…1.7, and weight is 0.7…0.9 kg.

As well the reversible (up-down) converter is produced, in which the features of wide-angle and of long focal length converters in one device are combined. It is intended for extension of the angle of the field of vision and focal length of zooms for professional and home video camcorders (which depends from installation version on lens).

All converters are produced with different fitting diameters and are supplied by connecting rings or adapters for working possibility with lens of different types.

For extension of change the focal length limits to the maximum values the built-in and withdrawal extenders are used, which are installed between lens and television camcorder. They are particularly reasonable supplied at shooting of playing close-up scenes, for instance, for sport program shooting. Depending on conditions of the shooting, the removable extenders can be used in combinations with TV-converter. But it is necessary to remember that unlike from TV-converters the extender reduces the optical performance which is proportional to the square of the extender extension factor.

The advantage of wide-angle extension is an increase the angle of the field of vision of the lens along with smaller size and weight in contrast with wide-angle converter, as well as smaller transparency losses. These accessories consist, as a rule, from one, sometimes from two or three negative lens for greater extension of the angle of the field of vision. The main disadvantage at shooting of wide-angle accessories is a possibility of the work with them only near minimum focal length and in mode of macro shooting only, by means of which the sub-focusing is executed. When a wide-angle accessory is used the lens speed does not change. The factor of the accessory extension is 0.7…0.8, the weight is 0.45…0.55 kg.

To make the effect of the vision with essential distortion of the picture the superwide-angle extensions named fish Eye are produced provided by angle of the field of vision equal to 130 degrees and more. They enlarge the depth, approaching the close objects. Due to distortion by the “barrel” it is the change of the frame sections which are found at up and down. For eliminating of the geometric distortions the accessories with aspherical surface are produced.

The lenses of the near shooting (close up) are the single plano-convex lenses. They are used in shooting of scientifically-popular programs about nature, when the small objects are shot. Their advantage is in significant extension of the shooting object (in 2…3 times) and in possibility of the scaling in whole range of the focal lengths that unfeasible at shooting in the “macro” mode. At present the lenses of the near shooting with focal lengths 300…1300 mm and the weight 0.35…0.5 kg are produced.

The effect accessories are the following:

• Multiplying lenses. These are the accessories, which are created the frequentative pictures. They can be with 3 or 6 edges (with different angles at top) and are assembled in revolving mount for making the necessary effect;
• Multiplying prisms with parallel edges. Create the repetitive picture. It can be used for creation of the quick motion effect;
• Lenses with clean centre (by different diameter of the clean centre). Create the clear picture in the centre of the frame and blurred picture at edges;
• Effect light filters. They are broadly used in television shooting for creation of visual effects, different light and color effects, raising artistic expressiveness of TV programs. It is necessary to note that the light filters are produced according the original technology and are made from optical glass, they are exactly processed and polished, checked by laser interferometer on parallelism of both sides and thickness of the filter. They are provided by increasing moisture and grease stability etc. When contaminated they can be cleaned by any organic solvent or soapy water.

Under all filter variety, produced at present by different foreign companies, it is necessary to decide in favor of the main types. The effect filters subdivide to several main groups according to the type of the obtained effect. During the shooting through any light filter a portion of light from picture is spent for the light effect making.

The ultraviolet filters (UV) are intended for absorption of the short-wave portion of spectrum, since ultraviolet rays though invisible for eye, create the colour haze. Often they are used for shooting in mountain terrain, on sea, as well as protective glass for front lenses. The ultraviolet filters are colorless.

Light filters of sky-blue color (Sky Light) are used for eliminating of bluish-green tone, appearing on unlighted foliage at clear sunny days. They exclude the shade, which can be sent by blue or other cool tone under upper light. Sky Light filters do not let pass the ultraviolet portion of spectrum, they have the pinkish tone and can be used also as protective glass.

The neutral light filters reduce the light flow, which is passing through lens. This is particularly advisable during shooting by lens with wide aperture, when because of low depth of the lens field resolution the expressiveness of the shooting object on defocused background and the volume effect is created. They are produced in three versions: ND2, ND4, ND8, with reducing of light flow in 2, 4, 8 times accordingly.

Low-contrast filters reduce the general contrast of the picture. They are right for portrait shooting. They are produced with miscellaneous degree of the reinforcement.

The diffusing filters are divided on misty, diffusion and softening (diffusing) filters.

The misty filters are intended for making of the mist or haze of different density. These filters are provided by the following features: the reduction of the contrast and saturation of the picture colour, the formation of halo around brightly luminous surfaces. The more filter density, the stronger display of these particularities. These filters can be used in combination with the other filters.

Diffusion filters are intended for the general or partial reduction of the picture sharpness under low reduction of the contrast. They soften the undesirable details, and picture gains “soft focus”.

Softening or diffusing (Soft Focus) filters are used for softening of the picture that it is particularly necessary at the shooting of portrait and lyrical scene. The net filters excluding the defects (the wrinkles, face spots etc.) of the shooting object are fallen at this category. In such filters the many-colored nets are used such as black, white, flesh-colored, red. The less net, the more result. Black net, softening picture, does not create the halo around bright subjects, reduces the contrast, muting a bright tone. White net creates the dissipating effect, softening a picture, forming haloes around brightly illuminated surfaces, reduces the contrast, and clarifies a shade. The color nets have even tonality of the whole picture.

Effect color light filters made from glass, mass colored plastic, or from colored gelatin, poured on glass, are intended for change of the picture color tonality, for receiving of the painted picture by established color. The color and saturation assortment of these light filters is wide. Color semi-filters are the filters, half of which is evenly painted, but the second half is transparent with sharp border of the transition. Light filters of this type are used for partial shading the picture, for instance, blue filter is assigned for the sky and water shading, yellow filter — for reception of the hot sun effect, etc. At this group are the double filters, such as double-colored, prepared by fifty-fifty cutting of sharp border. There are the yellow-green, blue-red and yellow-purple filters; the three-colored strip filters, divided on three parts with parallel borders, for instance, blue-yellow-purple, multicolored (the many-section) color sector filters, with color in each sector is different. At rotation of this filter it is possible to control by the position of different color fields on picture.

Shaded light filters are the most interesting since the color gamma is wide and varied. Either as color and semi-filters, they are intended for partial painting of pictures in wanted color. Density of coloring can be changed according to different linear laws and increases to edge that does the connecting border of the wedge practically imperceptible. Filters are manufactured both with one shading, and with two counter shading, etc.

The starry filters are intended for reception of starry effects from powerful light source. The brighter and less the size of the light source, the stronger the effect both from the source itself and from source picture on reflecting glass, water of metal surface. They are mostly used for night shooting and shooting on the stage. Depending on number of dispersing beams the starry filters are divided on 4-beam (Cross Screen — starry), 6-beam (Snow Cross — snow), 8-beam (Sunny Cross — solar), as well as 16-beam and etc.

Diffraction filters are intended for making of the glare color bright stars, rings, hyperboles interrupted by spectral beams, around bright light sources. These filters are based on diffraction laws on periodic structure, created by mechanical or holographic way. The lattice made by mechanical way, presents itself the collection of parallel equidistant touches of the same with frequency from group of ten to hundreds touches in one millimeter. Varying the frequency, the form, the depth and other parameters, it can possible to get the multiform effects. All diffraction filters are used in revolving mount.

Polarization light filters are used for eliminating or weakening of undesirable glare from wet, polished or brilliant surfaces. In the last case the color saturation often increases. They change the tonality of blue sky, making it at will darker. Also, the effect of polarization is used in shooting of the object on blue sky background, since is herewith suppressed the sky-blue color and an object (for instance, the mountains) is raised above noticeably. Polarization light filters are also manufactured in revolving mount. Under their use it is necessary to control the white balance, since the factor of light transition is decreased on 25% and the color balance is changed.

Light filters and the other accessories applicable for effect creation, are fixed on TV camcorder by means of compendium. The compendiums produced for modern video journalism camcorders, are differed by the design, the possibility of the simultaneous installation of several filters and accessories of the different diameters and by the installation on camcorder: on the lens mount directly, or on handle of the camcorder or on tripod of the camcorder. As a rule the compendium include two filter-holders, one of which is rotary (for functioning with polarization filter), blind (“harmony” or hard blind), connecting rings set of different diameter for possibility of the work with any camera and with any lens type (wide-angle, with internal focusing, standard and other).

Thereby at present to the specialists the wide choice of optical devices for journalist camcorders is offered, allowing creating the different effects. The aim of the user is in their skilful using for decision of the creative tasks.