Lobre s.r.l. was set up in Brescia in 1946 by the engineer Simone Marcucci and has been designing lenses and objectives for a variety of applications ever since. Its catalogue includes everything from the simple magnifying glass right up to microscope lenses, those for fixed headlight projector lenses, objectives and numerous other applications.
Commonly used optical lenses are called customised spherical lenses, as they are delimited by spherical surfaces. In a lens constructed like this, the optical axis is defined as the straight line passing through the two centres of the spherical caps that delimit it. The optical axis is the line passing through the centre of the curvature radii of the surfaces and, in plano-convex or plano-concave lenses, this is perpendicular to the surface and passes through the centre of the curvature radius of the other surface.
The centre of the customised spherical lenses is the point that has the feature of not diverting the light radii. The most significant element of a lens is the focus, which is defined as the point where light beams that are travelling parallel to the optical axis will converge. Its distance from the centre of the lens is called the focal length and is usually denoted with the letter F.
To construct the image of an object produced by the customised spherical lenses, one usually follows the path of two particular radii: one that starts from the top of the object, passes through the lens parallel to the optical axis and is then diverted towards the focal point, and the other one that starts at the top of the object and passes directly through the centre of the lens and continues onwards without any deviation. The intersection of the two radii defines the image point.