How a lens is built

In the case at hand, we will refer to convergent and divergent lenses. The first are those that, due to their characteristics, converge the parallel rays of light to the main axis, towards a point called focus. The characteristic design of these lenses is to be thicker in the center than in the edges.

Divergent lenses, on the other hand, are thicker at the edges and thin at the center, which causes the parallel rays of light as they pass through them to separate as if they were starting from a virtual point.

Lenses can be in their shape, flat, concave, convex or the combination of these types of surfaces. The convergent lenses are biconvex and the divergent biconcave lenses but there is also the plane-convex, plane-concave, meniscus-convex and meniscus-concave lens.

With regard to the production of the image, either by electronic or photographic means, the use of lenses, or as a whole, what is also called optics, is a definitive component in the quality of the image and the visual language of the product that is made.

The optics, lens or lenses, as they are regularly called, are

they are classified into two groups:

1. Fixed focal length lenses

2. Variable focal length lenses.

Among the first, there are fixed focal length lenses called fixed lenses: normal, angular and telephoto lenses, and the characteristic that defines them is to have a field of view determined according to their focal length. So-called normal lenses encompass a field of view with an approximate angle to the field of view of the human eye. On the other hand, the angles have a higher angle of view than the human eye, which allows a very wide field of view. Its determining feature is that it has a short focal length, unlike telephoto lenses that have a narrower angle of view and larger focal length than the normal lens, being the distance or focal length, the distance between the front of the lens and the point where the rays converge called focus.

Materially we can distinguish an angular lens from a telephoto lens, since the angular lenses are much shorter in longitudinal size than the normal ones, which in turn are shorter than the telephoto lenses.

Variable focal length lenses, usually called zooms, consist of several optical elements within the lens, some fixed and others mobile that allow in their internal actuation the change of the focal length of the lens, allowing in it, different focal lengths according to the range of the design of the lens. For example, a zoom of 12-120 mm, means that the lens has the probability of showing a field of view with all intermediate alternatives between 12 mm (angular) and 120 mm (telephoto).

This type of optics, lens or lens called zoom, has become the favorite of video production equipment, especially in the performances of Electronic News Gathering (ENG), because they facilitate the capture of images quickly in different circumstances and distances. Likewise, at the time of capture, they allow the movement of approach or distance from the object and the enclosure or opening of the visual angle within the same plane. This creates the sensation of movement and a space of selection of what you want to show, all this without the need to change the lens or the lens, which at a certain moment would mean time and the possibility of losing the moment that is sought or required.

At present, it has become common for video work, the use of fixed lenses and it is a fact that some digital cameras allow to exchange the use of lenses for those of 35 mm cameras. One of the main advantages of this fixed optic is its power of resolution and of course, its greater sensitivity to light, taking into account that it has fewer optical elements that interfere with the path that light must make through the lens.

An indispensable element that needs to be considered, apart from the focal length, when selecting a type of lens or lens, is the power of resolution. This is the lens's ability to reproduce the detail of the object it is intended to record. Fine optics, as they are often called, have a great power of resolution, even working in very low light conditions and with maximum apertures. This power of resolution has a greater impact depending on the size to which the object is to be enlarged. The high definition or the high definition (High Definition), in the new technology is more demanding with the definition and resolution of both the optics and the support.

Another important factor within these mentioned characteristics of the lenses, is the luminosity or ability to transmit light. On the scale that measures these apertures of the iris or diaphragm, the lower the unit that calls this capacity, the greater the luminosity of the lens, that is, a lens whose maximum aperture is 1.2 is more luminous than one whose aperture is 1.8 or 2.5. These luminous lenses are called High Speed or fast lenses and are usually fixed focal length lenses with maximum apertures of 1.2 or 1.4.

It is worth remembering Stanley Kubrick, who died in 1999, who used in his film Barry Lindon (1975), a lens specially designed for NASA, which was also used in the first trip to the Moon by astronauts to take photos. This lens had a maximum aperture, less than 1 (about 0.7), whereby Kubrick and cinematographer John Alcott filmed memorable period scenes, illuminating only with the light that came from the lit candles on the set.

In lenses of variable focal length, zooms, the luminosity is much lower than in fixed ones, because the amount of optical elements through which the light must pass, makes it difficult to match, in terms of luminosity, to the fixed lenses. The longer the focal length of the lens, the less luminosity it will be.

The brightness in the lenses is a decisive factor when choosing the optics for the different light conditions, because this quality together with the increasing sensitivity of the cameras and the photographic support, reduce costs and make production faster.

Of course, the video cameras currently available have also achieved great development in this regard. Digital systems, combined with the latest technologies in the manufacture of video lenses, are very valuable resources for the creation of moving images with a high resolution and remarkable behaviors in their sensitivity to light.