Television lenses of the third millennium beginning

By Leonid Chirkov

Review contents:
Television lenses of the third millennium beginning Television lenses Lenses from “Optics-Elite” Lenses from Angenieux New lenses from Canon E-cinema lenses from Fujinon Fujinon lenses for TV journalism and TV production

The science and technologies already past second millennium under curtain of XX age have proved that they “…can all. Well, almost all”. So in the third millennium instead of TV glass lenses, which are very expensive and fragile instruments, this is time to provide with its imitation, executed by means of integral optics. Theoretically this is simple task. Only one master device is made. Then it is necessary to write its hologram or, in other words, interference field of two beams. One of they get through lens, the other plays the reference role. Strictly speaking, record follows to execute for each allowed foreshortening; this is an operation more stodgy, than complex. In total weighty, it is enough big sized device, which is necessary to guard against impacts, humidity, sun light, low and high temperature and many others, will be replaced, due to integral optics (theoretically), by plate — fine, light, possibly inexpensive, probably shockproof, etc. It is need to repeat once more, that in theories all this is real, but… All of this is realizable if instead of laminated interference coverings to use persisting three-dimensional record in media by thickness in millimeter at least or more. Here is this great “small” obstacle brakes the progress in the field of integral optics and, in particular, in creation of television lenses of new generation.

For a long time shooting and television techniques was solely orientated (certainly, not from good life) on lenses with constant focal lengths. The different types of the shootings were provided by sets of removable lenses. But to accelerate their change, the special mechanism was used at one time — a turret (from French word tourelle — a small tower). The turret is the revolving disk with openings and landing places for lenses and afocal extensions. The simple rotation of turret it is possible to install quickly before camera required lens from set, selected in accordance with shooting mode. The improvement of optical systems production technology and (that extremely it is important), development of the methods of their calculation, including accounting syntheses (including computer), have allowed to develop and carry in practical the lenses with variable focal length. Presently even home video cameras are equipped such lenses, which are enough efficient.

The first reconfigurable lenses with variable focal length, or scaling (zooming) of the picture, were come up in medium of 1950-years. So the first television lens with manual realignment of the front focal length the Canon Company has submitted for the market in 1955.

Approximately all 1970-years in that sphere, which it is possible to name as television optics, have been passed the serious competitive fight between lenses with constant focal length and a novelty — the lenses with variable focal length or “zooms”. The modern television practically completely abandoned to lenses with constant focus. One of the reasons, naturally, a permanent deficit of time, which completely can come short for lens change. And simply on-worldly: one zoom always better than big set of “invariables”.

While the main product of TV optics are remained the lenses with constant focal length, which production is comparatively simply even under enough heavy requirements of the television to these products, in the world were acted many companies, risky to make and trade the professional television optics. Only in Europe it was a good ten of them. De facto presently it is a triad: Angenieux (in Europe), Canon and Fujinon (in Japan).

Fig. 1. Optical scheme of zoom lens

The modern lens is enough perfected device. Some simplified version of the optical scheme of the modern lens is on the following figure. In this lens composition are a few glasses (lenses), which, with some clause, can divide into three functional groups. The set 1 is a frontal group. Functionally its is that that is accepted to name by an object glass of the lens. To word, the group 3 is an eyepiece. The main function of the frontal group is a focusing of the lens. Its front and back glasses are still. Only internal glasses are moveable. This circumstance is emphasized by term “Inner Focus”.

The group 2 controls the main function of a zoom, namely a variable focal length. It is necessary to select two subgroups. The first of them is 2.1, which moves accordingly to linear law, the second of them moves accordingly to nonlinear law. As a rule, immediately after zoom group the iris diaphragm is set. The group 3 is a group of the still lenses. Exactly this group is provided the stillness of the picture planes, which the lens forms. There are exactly important its stillness and exact position in space since it is necessary to provide their joining with CCD surface (i. e. photo converters of the camcorder). In lens with built-in multiplexer an according group of lenses also falls into group 3.

As is well known, the surfaces of the lenses are spherical. At the last years the aspheric elements have begun to include in groups of the lenses. Their elements have provided the solution of many difficult problems of the aberration distortion suppressions. Also, a large number of the lenses in composition of modern lenses has back side (rather it is unattractive), i. e. a large number of the media section borders with miscellaneous factors of the light refraction, on which light flows are not only refracted, but also are reflected and partly polarized. As a whole, this is not only worsens the general transparency of the system, but also conducts to appearance glare. Modern technologies offer some efficient means for the fight with such troubles. The integral optics already it is enough “has became skilled” in production of clarified, contra glaring and other laminated coverings.

The modern TV lenses are obliged to be and are the twice-formatted on picture. These formats are the following: 4:3 and 16:9. Presently in television cameras CCD of several sizes are used, such as 2/3“, 1/2” and 1/3“. These numerals are the diagonal sizes of photosensitive part of the matrixes in inches. This is necessary to remember when you are interested of concrete lenses choice. At present the TV-production can be either studio or ‘beyond studio’ that is to say ‘field’, on nature. Television journalism is the next specific direction of TV-production. In some relations the news production is closer to last named direction, but is not absolutely the same. And quite separately are located some special types of the television shootings. The modern production of TV lenses is nearly copes with the impossible task of the lenses fabrication for all cases, but the lens specialization is remained as very important feature.

TV lens is a complex optical device and has some technical parameters, which collection gives the full belief about him. Amongst them there are such, which any potential consumer would like to know. The main group of zoom parameters include the focus parameters (zooming). The operational range of focal lengths is defined by minimum f_min and maximum f_max focal length values. However, in the first place a potential consumer is interested by multiplicity M of focal length change, or, in accordance with professional slang, of zooming. The factor M is defined as ratio of maximum and minimum values of focal lengths: M = f_max / f_min. These parameters are obligatory elements of any lens marking.

Fig. 2. View angle of the lens compliant with 2/3” CCD

The following valuable parameter of the lens is a field of vision. It value is accepted to mark as 2σ. The angular size of the field of vision is greatly depended from current focal length. This dependency is explained on figure 2. The numeric parameters on figure 2 are corresponded to CCD 2/3". It is necessary to notice that under greater values of the field of vision the minuteness of picture and, consequently, information saturation is higher, than under lower values. The higher angle values of the field of vision are typical for shooting in limited space.

To lenses parameters, about which it is necessary to know, also belongs the relative hole, usually marked in technical literature and prospects as o. Lens illumination value allows to compare luminosity of shooting objects with luminosity of their pictures. Lens illumination value is defined by means of remarkable mathematical rule, the known as “gold cross-section”. Well, a certain value, named as relative aperture, it is necessary multiply on the distance to shooting object and equate the total with square of corresponding focal length value. The relative aperture in a considerable extension is depended from acting focal length of zoom. It value is maximum under the smallest focal length and is minimum under highest focal length. As a rule, as consumer feature the normalized parameters are used. One more important feature is a minimum distance to shooting — S_min.

The modern lenses are automated completely. Their obligatory element now is a microprocessor, which controls all work functions in optimum mode. However in all lens is provided also a manual function that is manual control. In this mode the operator is provided by possibility, with orientating on him experience, to understand the light and play of light and color drawing, to choose own style of the illumination of the scenes and shooting objects.

At March 2002 (“625”, 03/2002, pp. 54-61) in article “Television optics 2001” we have represented the latest for that moment optical equipment for television. In particular, champions of multiplicity for that year have became the lenses Fujinon XA87×13,2E with M = 87 and Canon 86TELExs c M = 86. Now Fujinon, to example, offers the telescopic lens XA101×8,9 with multiplicity M = 101. For these optics masterpieces is hidden the exact calculation of the schemes which is possible only with provision of computing progress and, certainly, of glass processing technologies progress. Ii is not difficult to prove the general theorem, which confirms the possibility of the making of optical systems with any beforehand given characteristics and functions. But to make things as calculated — it is a labor, and enormous labor. Multiplicities above hundreds — this is a record even for modern technology.

During many ages the optometrists saw the same and very awful dream. Its name is aberrations. The highest accuracy of the optical devices processing, calculations and corrections has nearly removed this problem. Again, serious changes have occurred in materials, used for fabrication of the lenses. These are already not glassy oxides of the quartz. Calcium fluorite for instance as material for optical glasses now is used. On the opinion of, in particular, Canon specialists, exactly this material distinguishes the most ingenious ratio of high value of the refraction factor and small value of the dispersion factor.

The modern lenses are classified on CCD-matrix sizes, as well as on picture format: 4:3 or 16:9. But in this case the format can be switchable mostly. There are general-purpose devices, as well as specialized devices, for instance, instruments with high scale factors or telescopic lenses. The special lenses can be intended for functioning in studio or in field conditions. For showing of the sport competitions some special lenses are produced. And about this it is necessary to remember.

The modern television lens is a complex and automated device. Inherently, the whole stale work on lens control is transferred to automation, though this does not exclude and manual control, when such mode is required by operator.