In this paper the construction of both mechanically and optically compensated zoom lenses is discussed. Particular attention is paid to the Computer Optics Inc. Optically Compensated Zoom Lens as well as the Arriflex Variable Prime Lenses.
This paper summarizes two subjects; one is theoretical development of zoom lenses and another is their configurational advances.In the former part, a general zoom equation is presented and its paraxial analysis is, in general, derived. In the latter part, it is enumerated and analyzed newly developed configurations of zoom lenses, such as a built-in range extender, an electronically compensated zoomlens, a two-component telephoto type and others.
In the design of high performance optical systems, the goals of superior color correction and reduced cost can be achieved when abnormal dispersion liquids are incorporated into a design. A complicating factor in these designs is the potential for degraded performance due to the significant changes in refractive index of all liquids with temperature (dN/dt). The thermally induced performance changes of glass-liquid systems can be virtually eliminated through a combination of proper liquid selection (i.e. at least two liquids are required: one to provide color correction, and one to provide thermal compensation) and multi-temperature optimization (i.e. zooming in temperature). In this presentation, the required optical and thermal characteristics for the correcting and compensating liquids are developed and the optimization techniques are discussed. Finally, the optical performance of glass- liquid objectives using several correcting and compensating liquid pairs are contrasted with a similar all-glass design.
The process behind compact cameras, capable of achieving high zoom ratios are described. In addition to the development of a suitable new type of zoom lens, the internal focusing is essential to the design. The study focuses upon current major lens types, especially a three-group zoom lens which are composed of positive, positive and negative refractive powers for respective lens groups. First, requirements on the development of zoom lenses are described. Then properties of lens types are discussed. Using similar specifications, applications of standard zoom lenses providing higher aperture are shown. The characteristics of these zoom lenses are then summarized.
Hughes ELCAN has developed a family of video projector zoom lenses. These lenses cover a large range of optical parameters, i.e. zoom ratio, F number, projection distance, LCD size. Most configurations use only two moving groups accomplishing zoom, compensation, and focus functions. This particular architecture allows the design of a well corrected compact zoom lens. This paper presents the procedures for initial design, using the paraxial optics equations, and the final system design using the Code V.
By the lens module theory, an initial design containing the first and third order properties of the four-group video camera zoom system with zoom ratio of 14X, and its real lens design are presented. The optimum initial design with focal length range of 4.1139 to 55.6148mm is derived by assigning appropriate first order quantities and third order aberrations to each module along with the specific constraints required for optimization. In order to obtain the real lens system equivalent to each lens module, we have optimized each real lens group with the constraints composed of the first order quantities and all third order aberrations of module. In order words, a real lens for each group has been designed to match the first order quantities and third order aberrations at a given conjugates. Finally we have combined to establish an actual zoom system. The combination of the separately designed groups results in a system which satisfies the properties of the zoom system consisting of original lens modules.
The advent of the Advanced Photo System has led to more stringent requirements for high-performance photographic zoom lenses due to the increased enlarger magnification needed to form equivalent size prints from the smaller Kodak Advantix film negatives. Additionally, the trend towards more compact cameras that are easier to carry has reduced the space envelope alotted to the lens in NSLR cameras. Several novel designs that utilize the advantages of glass and plastic molded aspheres to achieve high performance, while maintaining a compact form factor, will be discussed.
Because of their obscured entrance pupils, variable focal length catadioptric object lenses have characteristics unlike their refractive counterparts. Zoom relay lenses are used to reimage an intermediate image formed by the objective without any reduction of entrance pupil diameter, but the relative aperture varies directly with focal length. Nonetheless the aberrations are correctable, and advantages of the combined field lens and focussing lens together with the liberal space constraints allow insertion of beam splitters, mirrors, temperature compensating lenses, and spectral range correctors. By adding different lenses on either or both conjugates of the relay lens, the zoom relay is used with a family of aspherized Maksutov objectives ranging in aperture form 100 to 300 millimeters.
The evolution of an unobscured all-reflective zoom optical system for utilization in the infrared spectrum is presented. The objective is to develop a system which has a flat image surface, wide field- of-view, spatially remote entrance pupil, 2:1 zoom range, and is spatially compact The optical system comprises three aspheric mirrors sharing a common optical axis where the primary mirror is spatially fixed with respect to the entrance pupil, and secondary and tertiary mirrors move during zoom. The field-of-view ranges from 2.2 degs by 2.2 degs to 4.4 degs by 4.4 degs. The focal ratio varies from F/4 to F/8. The inherent characteristics of this type optical system are discussed, as are design methods to control aberrations, distortion and anamorphic error over the zoom range. The baseline design configuration is presented along with MTF performance data. The results of tolerance sensitivity analysis are also discussed.
Optically compensated refractive zoom lenses use lens groups which are mechanically coupled at a fixed separation, moving between another set of fixed separation lens groups. Such systems exhibit an image position which oscillates about a mean focal plane as the lens is zoomed. These systems are simple to implement mechanically, but they have the disadvantage that they are bulky compared with equivalent mechanically compensated zoom lens types. In a catadioptric optical system we can exploit the same sort of mechanism by moving lens groups placed between (catadioptric) mirrors, and in this case the overall system can be compact. The simplest form of system of this type consists of one lens and one mirror and this has similarities to a three-lens optically compensated refractive zoom system. In this paper the first order analysis of optically compensated catadioptric systems is given and the design of some simple representative systems are developed.
The continued development of focal plane arrays of increasing size provides new challenges in the design of the associated imaging optics. The main aim must be to achieve an acceptable balance amongst a range of conflicting requirements, principally, optical performance, mass, space envelope and low cost. In this case the development of a high relative aperture zoom optic, operating in the 3 to 5 µm waveband, is described. The basic configuration is that of a mechanically compensated zoom objective with additional pupil relay optics. The relatively long focal length and high aperture of the optical system combined with the need for compactness presents particular problems regarding chromatic correction over this waveband. Whilst the conventional silicon/germanium combination is employed, this alone proved to be inadequate, hence the inclusion of diffractive surfaces, also the use of an additional high dispersion material. In order to maintain useful optical performance over the temperature range, a multi-sensor athermalization algorithm is derived to re-position the moving zoom groups. The design process is described, through to component testing.
A camera zoom lens produces a constant image size at constant relative aperture, which implies a varying field of view and varying entrance pupil size during zooming. In contrast, the zoom collimator of this paper is designed for a constant field angle and constant size entrance pupil, and this implies a varying image size and varying relative aperture during zooming. The optical design and engineering of a 10 to 1 zoom ratio, 2 to 5 pm waveband, diffraction limited infrared collimator is described. The application of the zoom system was a variable magnification scene generator, used to test infrared imaging and seeker systems. Although the field of view and relative aperture are modest, namely 2 degrees and F/5 at one zoom extreme, the required image quality was very high. RMS. aberration residuals of less than 1/10 at 2 µm wavelength for all field angles and for all zoom positions, were specified. The design adopted was an eight element, all spherical silicon and germanium re-imaged configuration.
IR materials have very high rates of index change with temperature. These index changes cause thermal defocusing that is an order of magnitude worse than that seen in the visible spectral band, and result in focus shifts usually too rapid to be compensated by housing material selection. The alternative is to actively compensate focus using motorized motions of a lens subgroup. Compensation of a zoom lens is more complex since the required thermal refocusing varies with zoom position. This paper presents a method for thermal compensation that is done in software for computer controlled, stepper motor driven zoom lenses. Compensation can be done to within an arbitrarily small temperature increment.
A 3-5 µm zoom lens system is designed with four moving components. Even though the optical system is designed to provide high resolution throughout the 4:1 zoom range, it is still compact. A special optimization method is used for finding the cam solution of the zoom lens . The polynomial equations from the optimization method are used for fitting zoom run during the optimization process. This method can minimize the cam sensitivity at the start of the first order design. The concept to achieve aberration balance is described. The detail design was accomplished through the use of a computer optimization program. A cam modification procedure is used to compensate the image shift after the final design. The one mrad image resolution requirement is achieved throughout the zoom range.
It is impossible for a zoom lens to image perfectly throughout its zoom range. That is, regardless of how complex a zoom system is made, there are necessarily residual aberrations. The principles of Hamiltonian optics can be used to determine the smallest level of such residual aberrations for a specific set of design requirements: zoom range, field of view, speed, etc. The best imagery that can be achieved by a zoom system, in the geometric limit, is referred to as the fundamental limit. The nature of the residual aberrations at the fundamental limit is investigated for a particular class of zoom system. It is found that the coefficients of the wave aberration function associated with each of the lens groups is not unique at the fundamental limit. As an example, the fundamental limit for a particular zoom system is determined, and the possibility of using this information in design is discussed.
Methods to solve paraxial pupil problems in zoom systems are not sufficiently developed up till now. A method intended to solve any paraxial pupil problems in different types of zoom systems is presented here. Among pupil problems such as the correction, stabilization, and required pupil location, stabilization is the most important. In the first stage of the method a zoom system is treated as a black box. Outside imaging parameters of this black box are determined by means of two-conjugate ray parameters. In the second stage of the method a zoom system is treated as a white box with the given number of thin components. Construction parameters of this white box, i.e. optical powers and spacings, are determined as those fulfilling the outside imaging parameters. In the third stage of the method components' kinematics is determined to keep both conjugations. The third moving component is called a pupil stabilizator, however, all moving components collaborate with each other to maintain the stabilization. To solve the non-linear system of equations the available standard mathematical software is used.
In any zoom lens, individual zoom groups experience both image and pupil magnification changes during zooming. Deliberate aberration can be introduced into zoom groups to produce an overall compensatory effect over the zoom range. When using a modular design approach, in which lens groups are designed independently, one has to take into account pupil matching among zoom groups. This is analogous to the design of relay optical systems. In a zoom lens, pupil matching becomes a dynamic problem. Perfect pupil matching among zoom groups in theory cannot be maintained for a continuum of zoom positions. With the deliberate introduction of pupil aberration on the group level, compensatory effects can be obtained and a more desirable pupil match can be achieved, resulting in better stability of system image performance over the zoom range. This paper presents a systematic explanation on how pupil spherical aberration can be used in controlling residual system distortion in zoom lenses. The study involves "black box" lens modules design with the help of computer ray trace program.
Most variable spherical aberration generators have differential moving components or floating elements, much like a regular zoom lens but with insignificantly small overall magnification change over the "zoom" range. The main purpose of the differential movements is to generate a variable amount of spherical aberration (SA). Such aberration generators can be used as standalone systems for aberration control or as subsystems for aberration compensation. The theory can also be applied to macro focusing mechanism as well as soft-focus mechanism. This paper presents a survey of different variable SA generation mechanisms. Examples of some applications of the theory are presented.
The principal part of the any zoom system is a two-component zoom system, which creates the necessary range of magnifications, focal lengths and fields of view. Over the last fcw years the utilization of the zoom systems has significantly increased. It is possible to avoid unnecessary design complica or by developing new design forms based on theory rather than adapting existing solutions. This paper explains the basic theory of two component zoom systems and presents a few new relatively simple high performance designs.