Zoom lenses have greatly improved to the extent that today many major performance characteristics are now equal to or come close to matching those of fixed focal length lenses. Some of these characteristics including size, weight, cost, producibility and general image performance are dependent on widely differing technologies. For example, optical design, coatings, refractive materials, surface types and the use of computers with suitable optical design software are just some of the technologies that when combined have driven the continuous development of zoom lenses and their optical designs.
Zoom lens optical designs have advanced for over a century with technology and manufacturing development transforming the capability of zoom lenses. Although there have been many different kinds of zoom lens developed, most fall into three main categories: fundamental, enabling, and improvement technology. Indeed, some technology and manufacturing developments had been crucial to zoom lens optical design development in a pioneering way and yet are now generally considered obvious or even simple. In comparison, other developments are incremental improvements that may be combined together like building blocks. Altogether, the capability of zoom lenses has greatly improved to the extent that today many major performance characteristics are now equal to or come close to matching those of fixed focal length lenses. Some of these characteristics including size, weight, cost, producibility, and general image performance are dependent on widely differing technologies. For example, optical design, coatings, refractive materials, surface types, and the use of computers with suitable optical design software are just some of the technologies that, when combined, have driven the continuous development of zoom lenses and their optical designs. Using zoom lens optical design examples taken from literature and patents, the evolution of zoom lens optical design technology and manufacture is described following a mainly historical order.
A lightweight, single-aperture, and multispectral imaging system operating from visible to long wavelength infrared has been manufactured and tested based on an innovative three-mirror anastigmat optical design. The complex off-axis aspherical toroidal mirrors of the optics have been obtained by electroforming replication from masters having a shape opposite to the mirror shape and manufactured as stand-alone parts by using five-axis single-point diamond turning. The technology is extendible to full free-form optics without any process modification enabling affordability of complex optics since multiple identical copies of the mirrors can be produced from each master. Moreover, thin (∼1 mm ) electroformed mirrors keep the imaging system mass less than 3 kg . With an effective focal length of 136 mm, the system is suitable for airborne surveillance applications and provides a full aperture F/# of 1.4, a field of view of 4.3×3.1 deg , and a nominal contrast better than 75% in the visible waveband at 25 cycles/mm . A beam splitter can be accommodated to provide two separated channels for two or more spectral wavebands. Stray light and thermostructural design has been performed to comply with airborne applications. Experimental results demonstrate the feasibility of the technology, although process improvements are required to reach the extremely demanding theoretical performance of the optical design.
A lightweight single-aperture and multi-spectral sensor operating from Visible to LWIR has been designed, manufactured and tested exploiting a Three Mirror Anastigmat (TMA) telescope featuring thin free-form mirrors electroformed from negative masters. Manufacturing complexity is in place only for the master realization, the contribution of which to the sensor cost decreases with the number of replicas. The TMA, suitable for airborne surveillance applications, has F/no. 1.4, focal length 136 mm and field of view 4.3° × 3.1°, and provides two channels, in the MWIR-LWIR and in the visible waveband. The nominal contrast is better than 75% in the visible at 25 cycles/mm. Electroformed 1 mm thick mirrors keep the sensor mass below 3 kg. Stray light and thermo-structural design has been done to comply with airborne conditions.
With the advent of digital camera systems which provide high performance imaging combined with reduced size,
weight and cost, this has created a demand for zoom lenses to meet new specific requirements. In addition, there is
also a need to meet preferred optical characteristics; therefore, contemporary zoom lens optical designs may become
less attractive for use with modern digital camera systems. Zoom lens optical designs which more closely match
digital camera requirements such as high resolution, high contrast, high relative illumination (for low picture
shading), low residual chromatic aberration and near telecentric radiation output at the image sensor, are described
in this paper. To achieve the desired requirements, the optical design power configuration of these zoom lenses
comprise four lens groups, with a first negatively powered lens group followed by three positively powered lens
groups. To provide zooming, a movable optical stop is located after the negatively powered lens group and is
followed by two positively powered movable lens groups. Additional features including low ‘breathing’ throughout
the focus and zoom ranges are also described via the optical design examples given.
Specific developments in optical technology over the past 30 years including refractive materials, thin film coatings, and surface profiles will be discussed. A large variety of optical designs which depend on some of these developments will be described. The optical design examples presented will cover the infrared, visible, ultraviolet, and combinations of these wavebands. A novel multiwaveband optical system that utilizes many of these developments will be illustrated in several possible configurations to meet different application requirements. A summary of the technologies employed in all of the optical design examples will indicate whether or not there may be trends in optical technology development. The optical design examples will be taken from issued Patents or published Patent applications, and hence their optical prescriptions will be available for detailed analysis.
Specific developments in optical technology over the past thirty years including refractive materials, thin film
coatings and surface profiles will be discussed. A large variety of optical designs which depend on some of these
developments will be described. The optical design examples presented will cover the infrared, visible, ultraviolet and
combinations of these wavebands. A novel multi-waveband optical system that utilizes many of these developments will
be illustrated in several possible configurations to meet different application requirements. A summary of the
technologies employed in all of the optical design examples will indicate whether or not there may be trends in optical
technology development. The optical design examples will be taken from issued Patents or published Patent applications
and hence their optical prescriptions will be available for detailed analysis.
Variable length viewfinders which provide constant focus, magnification and pupil conjugate stability, in motion picture camera systems employing different size zoom lens objectives, are described.
The optical design of a visible waveband, high performance zoom lens objective system, which utilizes aspherical surfaces and a zoom group internal stop, is described.
The optical design of a high performance short focal length lens system and several derivatives thereof which cover the Super 16 mm film format is described. Particular areas of discussion include the use of internal close focusing optics to eliminate the need for precision focusing mechanics and the use of multiple aspheric surfaces, as well as, internal filtration to reduce system size, weight and cost. Other areas, concerning optical `breathing', distortion and material choice, especially very high index glasses, are also addressed.
The optical design of an unconventional telephoto lens, which employs a single front objective element with spherical surfaces, one anomalous dispersion glass element and multiple liquid lens elements, is described. Particular areas of discussion include the utilization of internal zoom optics for constant aperture focusing to macro magnifications and abnormal dispersion liquid lens elements for high order chromatic aberration correction, as well as, passive optical athermalization of back focus and image quality. Other areas concerning lens system size, volume, weight, cost, and spectral transmission are also addressed.
Observations made on the macro focus conditions of fixed focal length lenses are used to provide an unusual but simple approach to appreciating the first order principles of zoom optics.
A long focal length close focusing zoom lens for the visible waveband which rivals the performance of fixed long focal length lenses is described. Particular areas of discussion include, the utilization of anomalous glasses to control secondary color and the choice of focus system configuration to minimize breathing, provide continuous close focusing to macro magnifications and the reduction of the number of large diameter elements required.
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