Electronic systems are rapidly replacing photographic systems for most imaging applications, and in a short period of time the actual size of the sensor has been decreasing. For consumer applications the half-inch CCD is replaced by the one-third inch CCD, and the quarter-inch CCD now has been introduced. Assuming no loss of pixels, lens designs for the newer formats could be derived by simply scaling down the existing larger format designs, changing the thickness slightly to accommodate the necessary minimum edges and spaces. But by recognizing that a minimum edge of 1 mm is 25% of the 4 mm image diagonal for a quarter- inch CCD, it becomes evident that even if conventional spherical glass lens technology is employed a new type of lens design is needed. Because the lens element volumes are so small, however, consideration of molded lenses, either glass or plastic, would appear worthwhile. More particularly for consumer and commercial applications most lenses 'zoom' because there are no surplus pixels, foregoing the possibility of electronic 'zooming' to effect a change of angular resolution of the object. The following describes the development of vari-focal and zoom lenses for small image formats that can be fabricated entirely by molding processes.

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.

The world's largest refractive zoom optical system was designed and manufactured by Eidolon Corporation. Four afocal zoom systems were built as part of a mobile, laser radar tracking systems. Each zoom had an aperture of 12.5 inches and a magnification range of 1x to 2x.

Submarine periscopes often provide a field change mechanism but there is a distinct preference for fixed magnifications for immediate awareness of range. However for a variety of reasons, the standard periscope is being succeeded by television. Even high definition TV is restricted in displayed resolution points compared with a direct vision periscope, therefore as apparent size is now dependent on the display, a continuous zoom is suggested to ensure relevance of the captured image. The need for steering and stabilization of the sight line and viewing through a window, within the bounds of an unobtrusive and seaworthy package present special optical problems. A stable entrance pupil must be projected onto the window beyond the line of sight prism. It follows that the optical system incorporates a relay stage to provide a real aperture stop and that configuration changes on both sides of the intermediate image are necessary to control the entrance pupil. Compact zoom lenses are usually based on Galilean telescopes and the moving group diverging; in contrast this zoom periscope is based on the Kepler type and all the lens groups are converging. The system provides an 8:1 zoom range, is unconstrained in overall length but fits a standard 6 multiplied by 40 ocular within a tube of 50 mm in diameter. A disadvantage is the motion of moving lens groups through a focus with a risk of blemishes becoming visible but the image quality is hardly inferior to a traditional layout using interchangeable lenses.

OCA, under contract to Spar Aerospace, has developed a space-qualified zoom color video camera. The optics are a 9.3:1 f/2 zoom lens under digital servo control, using only two moving groups to accomplish zoom, compensation, and focus over an object distance range from 355 mm to infinity. Accomplishing three functions with two moving groups both improves reliability and allows better aberration correction than conventional zoom lenses using front-element motion to focus for range. The detector is a single chip array with integral color filter array. Important lens features include excellent image quality; performance in a near-earth orbit for 10 years without maintenance; and the development of an algorithm allowing accurate photogrammetric ranging from 355 mm to 10 meters.

Zoom projection lenses have been designed that have an entrance pupil that remains stationary during zooming and an operative aperture stop distinct from the system's physical stop that moves through the lens surfaces as zooming takes place. The fixed entrance pupil allows for efficient coupling to the light source throughout the magnification change. By allowing the stop to move through the lens, the lens element sizes and aberration contributions can be minimized. The concept of the operative stop can be employed for both positive and negative first-group configurations. For wide angle projection of 64 degrees total angle, a lens system with a negative front group followed by a positive zooming group has been designed with a relative aperture of f/4.5. Applications involving large LCD panels as light valves require the use of plastic optical materials with aspherical surfaces to minimize manufacturing costs. Concentrated high wattage light sources introduce temperature variations that impose additional constraints on the optical design. By combining plastic and glass elements the image position and aberration correction are stabilized throughout a plus or minus 25 degree Celsius temperature change.

First and third order principles for location of the aperture stop in infrared zoom lens systems are discussed. Factors to be considered include lens diameters, third order aberrations, chromatic correction, and illumination requirements at the image plane. In particular, the importance of aperture stop location in infrared applications is considered. An example illustrating these principles is presented.

Infrared zooms, continuous and two positions, are becoming more prevalent. Two position zooms are generally longer than other equivalent two fields of view systems, but have smaller total volumes since the switching group in the second field of view requires storage space when not in use. The optically compensated compact zoom with a negative zooming group requires at least three groups, a positive objective group, a negative zooming group and a positive focusing group. Generally these groups are made up of one or two elements. With the uses of single point diamond turned aspheres and diffractives, the three groups can be made of a single element each. The three element optically compensated two position zoom can be used in the longwave 8 - 12 micrometer region or the midwave 3 - 5 micrometer region. It can be employed as a simple imager or as an objective in an afocal telescope or in a reimager. The three element zoom can have magnifications from 3x to 5.5x with optical invariant as large as 1.61 mm. The short focal length of a zoom can be as small as 17 mm in one design, while the long focal length of another zoom can be as great as 275 mm.

This paper describes the specific design considerations and performance evaluation for ELOP's MLZFS (modular lightweight zoom FLIR system) utilizing a new athermal wide magnification range IR zoom telescope. The following aspects of the development work are discussed in this paper: MTF and MRT characteristics of the FLIR for different temperatures; comparison with existing zoom systems and with systems of discrete magnification change; calculation of lens group positions as a function of magnification and temperature, including interpolation analyses of these dependencies; implemented methods for narcissus effect reduction at the lowest magnification mode, including development of a new AR coating; critical tolerance analyses; mechanical and electro-mechanical design, answering high accuracy requirements; adjustment and calibration of the zoom system by use of an IR interferometer.

Binary optics element (BOE) used to correct the aberrations of zoom lens, especially to control secondary spectrum in apochromatic zoom lens, are considered. Principles and methods are presented. The advantages in improving image quality and simplifying construction are illustrated through the design example.

The need of coma at the exit pupil of a telescope for a scanning IR camera is well known. However, in some cases it is impossible to introduce the required pupil coma if there are not enough degrees of freedom. This paper describes the use of a binary surface in a DFOV telescope so that pupil aberrations are properly controlled. The design has been performed on an already existing telescope, maintaining design philosophy. Several positions of the surface are considered. Comparison among all possible configurations is evaluated in terms of image and radiometric quality as well as weight and cost savings. The effect of the binary surface on the system performance over the operative temperature range is also studied.

In high performance optical systems, a frequent requirement is 'athermalization' or the stabilization of optical performance with environmental temperature. This is particularly relevant in the case of refracting infrared systems for which the variations of refractive index as a function of temperature are relatively large. In this paper, as an example of an athermalization problem, the approach adopted for the stabilization of an infrared multi- magnification 'zoom' telescope objective is reviewed and the mechanism devised for introducing the necessary adjustments is described. Finally, the variation in performance of an actual athermalized system, following heat soak over a temperature range of 130 degrees Celsius, is discussed. The telescope, which was designed for use in the 8.0 micrometer to 13.0 micrometer waveband, provides a set of four fixed magnifications ranging from X3.5 to X20. It employs germanium and zinc selenide as refracting materials.

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.

In this paper, the varifocal differential equation theory of zoom lenses is comprehensively introduced, its applications are discussed. Practices show that this theory is accurate and convenient.

To determine paraxial properties of the general four-component zoom system with mechanical compensation we must have the methods to obtain the optical power distribution and test and evaluate kinematics. There are two important approaches to general conception of a four- component zoom system. The first refers to the expansion of the method for three types of zoom systems. According to the location of an object and image in relation to a zoom system, we distinguish the following zoom systems: variable focal lenses, projection or reproduction systems, and afocal attachments. The second refers to the expansion of kinematic possibilities of all zoom components and even an object plane. Research led to the conclusion that knowing the marginal positions and extreme values of the main useful parameters connected with them is quite sufficient to obtain the optical power distribution of the individual components. Changing the input data we may minimize the longitudinal dimension of the zoom system. Sort of a zoom system is determined by paraxial aperture coordinates at the edges of a zoom system. The first optical power is calculated from the equation being four degrees of polynomial. We have four solutions of this equation and have four propositions of the optical power distributions in a four-component zoom system. All remaining optical powers in the four-component zoom system are expressed by the first optical power. Calculation of optical powers in this way means that the zoom system is good only in both marginal positions. Research led to the statement that, optical conjugate and fixed image location are determined from a quadratic equation. To verify kinematics of the zoom system it is necessary to determine the variation of the main useful parameter and, if required, variation of movements of the first and fourth component. After kinematic calculations we should first test whether the travel from start to the final position is smooth. Later we evaluate kinematics and, if possible, correct it by mentioned changes or even by modification of marginal positions.

This paper presents the procedures for an initial design containing the first and third order aberrations of a four-group, rear focus video camera zoom lens using lens modules, and the real lens design from an initial design. Lens modules in the zoom system can explicitly describe the first and third order properties of each group without detailed design. The optimum initial design with a zoom ratio of about 10X and a focal length range of 6 to 60 mm is derived by assigning appropriate first and third order aberrations to each module along with the specific constraints required for optimization. For a real lens design of each group, we set up the simultaneous equations for the first and third order aberrations, and the solutions result in the optical systems which satisfy the properties of original lens modules. As a result, the design of a zoom system using lens modules is broken down into the simple problem of designing the individual groups to satisfy sets of the first and third order properties, and quickly provides the optimum system.

Analytical expressions for evaluating zoom system parameters are given, along with properties of the resulting zoom system types. Relationships of the moving component are derived, taking into account overall dimensional limits, and are shown with two examples. The possibilities of reducing image defocus with zoom are discussed.

The global synthesis and global optimization methods developed recently are based on numerical methods of search of the global extremum of the merit function. Such methods are developed without paying due regard to image formation law and with no account of the role of the separate optical subsystem for appearance of aberrations. These circumstances don't make possible effective formalization of the problem of obtaining the starting system. It should be mentioned that 'before the computer epoch' the optical system design was characterized by wide use of analytic methods based upon classical aberration theory. These methods were used both for optical system designing and the detailed study of their potential possibilities. The efficiency of said methods is proved by the possibility for an optical designer to get almost 'by hand' a real optical system. The labor-consuming and tedious procedure of the real system aberration correction took place only at final stages of operational development of the optical systems. The paper describes the author's methodology of starting system synthesis. This methodology makes possible numeric- and analytical-construction of optical systems on the basis of wide use of the classical theory of aberrations and it substantially develops 'before the computer epoch' approaches. Let us consider a set of principal peculiarities of the offered methods of starting system synthesis and the results of particular use of such methods.

In many cases the time for optical system design can be considerably reduced if the possibility exists of adoption of the real optical system with acceptable aberration properties and characteristics close to the desired ones (the so-called prototype). In order to use such a possibility a certain work has been fulfilled for realizing the data base with ready optical systems, the results of the work being reported here at our conference in another paper. But the prototype adoption requires us to carry out profound analysis of aberration properties of the possible prototypes and to select the most acceptable one. The use of classical approaches of aberration analysis doesn't permit us to investigate thoroughly the interconnection between the aberration properties and the ones of the lens forms. The questions are: how to reveal the potential possibilities of the lens forms? How to find the most optimal fields of use of the real optical systems and how to select such a lens form that can provide the best imaging? In connection with the foregoing we developed a principally new approach for investigations of the aberration analysis and limiting possibilities of optical systems. This approach is based on investigation of behavior of the aberration functionals depending on the special method of variation of an angular field of view and an aperture.

All-reflective telescopes have found significant utilization in the astronomical community, government, and industry. Until recently, the concept of an all-reflective zoom telescope, particularly having an unobscured pupil, with meaningful capabilities was unknown. Several designs of unobscured-pupil zoom telescopes comprising only three mirrors are presented. The designs discussed have fields-of-view up to 3 degrees by 3 degrees, F/#s as low as 3 and zoom ratios of up to 4:1. The rms geometric blur diameter for one zoom telescope, having a 4:1 zooming range, was found to be 45 (mu) radians in the wide FOV condition (2 degrees by 2 degrees and F/4).

Two forms of reflective zoom systems have been described in the literature. Rah & Lee (1989) and Johnson et alia (1990) show rotationally symmetric systems comprising a Cassegrain imager, followed by an inverse Cassegrain relay. This form suffers from large values of central obscuration at some zoom positions and uses independent motion of all four mirrors to achieve a stationary image. These systems employ spherical and simple conic surfaces to achieve appropriate aberration correction. Earlier Woehl (1981) described an all reflective zoom relay system, using multiple moving off-axis mirrors for use in optical beam shaping applications. The systems described here are combinations of the two types, having a fixed conventional Cassegrain imager, used at a small off-set field angle, to allow the re-imaging ray beams to pass without further obscuration through a set of off-axis zooming mirrors, to a final image. The relay mirror curvatures and separations are chosen to achieve the required zoom ratio and fixed image location, and appropriate tilts and decentrations may be impressed upon the relay elements to permit unhindered ray passage.

The distinction between mechanically and optically compensated zoom systems has an interesting counterpart in certain catadioptric systems. The simplest such system is very simple indeed: a front refractive air-spaced nearly afocal doublet near the front focus of a spherical concave mirror. The front positive lens and the mirror have a fixed separation and the following negative lens moves back and forth in the space between, while also being traversed again by the focused light from the mirror. By having the negative lens used in double pass during its zooming motion a quartic focus curve can be obtained. The image falls near the center of the front positive lens, where a detector can be placed. A sample design with a 2.5X zoom ratio is described. The two front lenses are germanium and it zooms from an f/2.0, 5.0 degree diameter field to an f/5.0, 2.0 degree diameter field with good image quality.