It is sometimes necessary to go back to basics when too many lens design requirements are suspected of drastically reducing the potential solution set. Results from a study of a family of plastic-glass triplets that have to be temperature compensated as well as optically corrected, reveal the limited number of promising solutions. At this point, logical decisions can be made to increase the set of potential solutions. This culminated in the design for the lens used in Kodak's "EKTRAMAX" Camera. The design is compared with several all glass solutions, and justification for using an asphere is discussed.
The optical system design of the ATMOS Fourier transform spectrometer to be operated from SpaceLab for the measurement of stratospheric trace molecules contains features which enable it to achieve the required fringe contrast of 80% and spectral resolution of .02 cm-1 (apodized) over a spectral range of 2-16 µm. In particular, the design for high performance and stability is based on the following key features, which alleviate to a substantial degree the usual requirements for alignment precision: 1. "cat's eye" mirror configuration in the two arms of the interferometer for retroreflection stability. 2. tilt-compensated system of beamsplitter, compensator and fold mirrors for wavefront directional stability. 3. paraboloidal "cat's eye" primary mirror for wavefront stability against shear. 4. rotable compensator for matching chromatic dispersion. 5. wedged refractive components to avoid channel spectra due to the Fabry-Perot effect.
Once a Cassegrain telescope has been selected for an application, only four orthogonal parameters - back focal length, system f/number, primary mirror f/number, and system aperture diameter - need be specified in order to predict the first-order performance of the entire optical system. Frequently, one or more of these parameters, as well as the form of third-order aberration correction, are allowed as variables and, therefore, can be used to optimize the system for performance, optical tolerance sensitivity, and cost. A set of parametric equations ("K" factors) has been developed so that this optimization can be performed before resorting to any detailed optical design and the subsequent evaluation of optical sensitivity. This paper describes the variables and the parametric equations, as well as the engineering scenario into which they fit. Examples of the ways in which they are combined with structural and thermal engineering technologies to produce an optimum design are discussed.
MTF tolerancing has not been a practical tool in the past, due to prohibitively expensive computer costs, in combination with lens designer calculations that are both extensive and dull. The design and use of a new computer program is described to demonstrate that the majority of the drudgery and computation costs are no longer necessary. Given the nominal design and the spatial frequency of interest, the program automatically generates a default set of tolerances, using defined boundaries and compensators, and predicts fabricated MTF performance. The user can override any of the assumptions to easily tailor the MTF drop, constraints, and compensators to those most appropriate to the specific manufacturing process and end use intended. RMS wavefront error can be used instead of MTF if appropriate. Examples are provided including computer-generated tables that can be directly used by an optomechanical designer.
The performance of optical systems is often specified in terms of encircled energy. It is difficult to assign fabrication and assembly tolerances to such systems because there is no simple way to predict the combined effect of tolerances on encircled energy. This paper presents a new, simple formula which, while not exact, can be used to quickly give approximate answers to many tolerancing questions. It is based on diffraction theory and gives some interesting insights into how aberrations, surface figure tolerances, and environmental perturbatons affect encircled energy.
The unwanted sunlight that enters a coronagraph through the diffraction process is the li iting factor for viewing the solar corona. The techniques initiated by B. Lyotl and expanded by Newkirk and Bohlin2 for coronagraphs with an external occulating assembly are presented. Scientific requirements for even better stray light suppression in the inner corona, and for observation of a broader spectrum now call for more sophisticated optical designs. The approaches for these improved characteristics, the problems they present and the methods to overcome these problems in the coronagraph for the International Solar Polar Mission (ISPM) are discussed.
The NASA Space Telescope (ST) is a 2.4-m aperture, f/24 Ritchey-Chretien telescope coupled to five on-board astronomical scientific packages. The very accurate line-of-sight stability required by ST during operating periods of up to 24 hours is maintained by the Pointing Control System whose optical system, the Fine Guidance Subsystem (FGS), is described. The Pointing Control System includes three identical FGSs, any two of which provide line-of-sight stabilization by tracking guide stars while the third performs astrometry. The optical design of each provides a well-corrected demagnified pupil at which the fine guidance field of view is scanned. Traditionally, field-aberration correction is performed by placing a refractive field group near the telescope image plane. Designs of this type are difficult to correct and complex, and require large and difficult-to-manufacture elements. The optical system for the ST FGS performs the field aberration correction within the FGS near a pupil plane measuring only 52.7 mm. The refractive group thus required is relatively small and easily manufactured. The design, up to that pupil plane, consists of a collimating mirror located after the telescope image and a five-element refractive group placed just before the pupil plane. The design is simple and easily corrected, and offers substantial advantages over the traditional approach in terms of manufacturability.
The use of Fresnel lenses is expanding rapidly and they are now found in highly sophisticated optical systems. Their use has helped to solve many difficult optical problems but has also introduced some new design considerations. This paper will explain some of the advantages as well as some of the limitations of Fresnel lenses. "Special" optical design problems related to Fresnels will be discussed briefly. A description of tooling and part manufacturing methods and their related tolerances will be covered. Examples of existing Fresnel and "hybrid" systems will be given. On-going improvements and future developments that will make the use of Fresnels even more widespread will be described.
Applications of the Cooley-Tukey Fast Fourier Transform (FFT) algorithm to varied computer analysis problems of EO systems are presented. EO systems synthesized by models using the FFT are laser monopulse trackers, COAT, and null trackers such as quadrant detector and spinning reticle seekers. Computation time reductions in excess of 600 times have been demonstrated by the introduction of the FFT.
Over the last several years there has been a growing consumer interest in Large Screen Television; large screen being defined as a 45 inch to 96 inch diagonal image. Present technology accomplishes this size imagery by using a lens to project a CRT image onto a viewing screen. Systems being manufactured today consist of front or rear screens, one or more CRT's and one or more lenses. The primary performance requirement most difficult to achieve economically is sufficient light output to permit comfortable viewing with a high ambient light level. This requirement, in conjunction with maintaining image quality, a reasonable configuration and low cost, established the need for inexpensive large aperture lenses. Several types of all-plastic objectives and large plastic Schmidt correctors are presently in production at U. S. Precision Lens to meet this growing requirement. The following discussion describes the optical design of the large refracting systems and some of the difficulties associated with these designs.
It is the task of an optomechanical engineer, starting with a lens design provided by the optical designer, to devise a structure which holds various components of a lens in proper axial and radial alignment. This structure, the lens barrel, must provide a means of interfacing with the customer's system, and must be designed so as to maintain optical and mechanical integrity under a multitude of environmental conditions. This discussion encompasses the design and analysis efforts undertaken by the optomechanical engineer to comply with this requirement. Additionally, some special areas of concern to the optomechanical engineer such as various centration and assembly techniques, cementing of optical components, sealing and leak rate analyses and reliability estimates of lens assemblies are discussed.
Military optical systems must operate over a wide temperature range and the effect of temperature change on the performance of some optical systems is described. Methods used to counteract such variations in optical properties range from servo-controlled motion of the components and bi-metal mounts with reciprocating motions to, as this paper describes, a simple choice of appropriate optical and mount materials. The optical systems considered include single and doublet lenses, laser beam expander and high quality imaging systems.
Aerial reconnaissance optical systems are often subjected to extremes in thermal environ-ment. Designers have been able to engineer systems which maintain stable performance over a wide range of steady-state temperatures. But, how long does it take a reconnaissance system to reach steady state after being subjected to a thermal shock (or step function)? This paper reports on experimental measurements made on several long focal length reconnaissance lenses exposed to thermal step functions. The most significant finding showed that the thermal recovery time is on the order of hours....a period during which the recon-naissance mission may already have been completed.
The traditional submarine periscope optical layout and the modern high powered laser system represent a first order example of incompatibility. Recent requests for a laser rangefinding capability built into a submarine periscope system have precipitated a new optical design configuration that eliminates most of the inherent problems, making the combination feasible. The evolution of this new design configuration and some of its unique characteristics will be presented.
The Nd:YAG laser is finding more uses every day, in both military and commercial applications. The laser is now treated more as a component than a separate system, and this trend has led to a whole new set of engineering challenges. The layout of an integrated system, optical design considerations, damage problems, alignment needs and techniques, and integrated system testing will all be discussed in this paper. System layout must take into account all interfaces, especially from a maintainability viewpoint, and often includes the use of a common optical path for several subsystems. Optical design problems include a spectrum which is much wider than normal, restrictions on intermediate foci, and a new meaning to the term "multiple configurations". Careful attention must be paid to laser-induced damage of both people and hardware. Narcissus is the biggest nuisance, and the use of cemented surfaces is severely restricted. Elements must sometimes be added to avoid problems. Alignment, both internally (between subsystems), and externally (boresight) must be a major design factor. Finally, testing requirements often influence system layout. Some examples of design tricks and gadgets are included, based on both a military rangefinder and a com-mercial welder system.
Basic principles of stray radiation suppression are employed in a FORTRAN computer pro-gram that assists in the design of well-baffled axially symmetric optical systems. Called GOSBOP (General Optical System Baffle Optimization Program) , this program can design the baffle structure of a typical system according to the user's specifications in less than a second on a CYBER 175 computer. The program can also be used in conjunction with a new version of the first APART (Arizona's Paraxial Analysis of Radiation Transfer) subprogram to design and evaluate a baffled optical system in a single computer run with a minimal amount of input. The programs enable the user to identify and eliminate troublesome single diffuse scattering paths so that a preliminary design can be optimized in terms of both optical performance and stray radiation suppression in only a few successive computer runs. As an example, the technique is applied to optimizing the baffle structure of a typical Cassegrain telescope such that the stray radiation reaching the image plane is reduced by up to three orders of magnitude. The stray radiation rejection of the final design compares favorably with relatively more complicated designs.
It is well known that the decentering in the lens manufacturing process decreases MTF-value of lenses. A computer simulation method is developed which estimates loss of the yield in the manufacturing process caused by decentering. The method is useful to evaluate the productability of the designed lenses for massproduction, and, moreover, will give proper suggestions to improve the yield without changing lens element. This method also enables us to select proper lens type. The method to improve the yield is discussed in detail referring several examples.
I have spoken several times, in different locations, about the Multiple Mirror Telescope and what it is. This is the last time, at least at SPIE. In this engineering symposium it would be appropriate to discuss some of the lessons that we have learned from the project. This will include both positive and negative lessons along with some illustrations which will help you understand why I consider them something we have learned. The comments made here are to be interpreted as mine and will be primarily related to the optical fabrication. Others on the project may view some of these problems in a different light!
An advanced Holographic One-Tube Goggle (HOT Goggle') has been designed for the U.S. Army Research. and Development Commands,' Night Vision and Electro-Optics Laboratory, Fort Belvoir, VA. The goggle is essentially a unit power night-vision, electro-optical sight consisting of an 'objective lens, image intensifier tube (converting visual and near-IR. radiation to visual at 0.5430 p.m), and an eyepiece. The eyepiece portion is of particular interest, as it uses two diffraction optical elements to provide the user with a biocular view of the output of the intensifier tube. Since the goggle is designed for use by ground troops, the physical. requirements are for a lightweight, low-moment unit that is compatible with the infantry helmet and gas mask. Optical requirements include: milliradian resolution, large exit pupils, interpupillary adjustment, large field of view overlap, and low distortion. The use of diffraction optical elements allows the user the unique ability to simultaneously view and superimpose the actual and intensified scenes.
The infrared scanning optical system to be considered is an 8 to 11. 5Ã‚Âµm dual-field-of-view configuration. With production, the ultimate goal of such a system--a cost-effective, productioncompatible design--assembly and alignment methodology is imperative. The optical design approach of previous configurations was modified so as to provide a modular system whereby preassembled, aligned, and tested modules can be "bolted together" and, with a minimum of adjustments, yield an acceptable level of performance. This paper discusses many of the optomechanical design tradeoffs which lead to a final modular system design. Module assembly, alignment, and test methodology are discussed.
The historical background, of U.S. Army individual night vision, goggles is briefly traced and the current status is summarized, leading to the conclusion that a dramatic reduction in unit cost is essential for maximum military utilization of such devices. System. requirements are outlined for low cost night vision goggles. A. current development program is described in which low cost is achieved by use of one image intensifier tube, by extensive use of injection molded aspheric plastic optical elements and by molded Plastic mechanical components. System concepts and design. considerations are presented.
There are two general types of systems for performing the imaging function in a copying machine. The first is the scanning type in which successive portions of the original are sequentially imaged on the continuously moving photoreceptor. These systems can usually be fitted into a comparatively small space, but result in a relatively high process velocity, thus imposing velocity constraints on other machine functions. The second is the full-frame type in which a complete image of the original is formed, at one time, on the (flat) photo-receptor. These systems permit, for a given copy rate, use of minimum process velocity, but require comparatively more space, resulting in an undesirable increase in size. Both types have additional interactions affecting machine performance parameters that should be considered at the earliest stages of architecture development. The various interactions will be discussed and the effects of these interactions on selected, existing copying machines described.
The use of electro-optics in sophisticated quality control systems has long been a standard in the machine tool and allied production industries. In the printing industry, however, apart fro, recent technological advances in optical character recognition, page scanners, and print character generators, little has been done in the field of printing quality control. This paper describes the relationship of electro-optical scanner systems for quality control in printing instruments of value (e.g. bank notes, Travelers Cheques etc.) and the subjective techniques currently employed by printers to evaluate such documents. Involved in this study is the application of image analysis, including spatial frequencies, authenticity verification, and processing techniques for the design of high speed quality control document processing systems.
Pictures have been taken with several miniature cameras, the smallest of which is 1/8" x 1/8" wide and .030 " thick, the thickness dimension being aligned to the object being photographed. When cut to size, most available films and thin filters can be used. However, the object or surface being photographed must be within zero to .005" of the camera sensing face to produce pictures of .001" resolution. Thus, the camera may have endoscopic applications in medical diagnostic and industrial evaulation. The author has a patent pending on the camera.
A new holographic information display element has been developed. The element is applicable to a superimposed information display in a camera finder or window display. The types of hologram is image and volume type hologram. The multiple information display can be realized by utilizing the sharp coupling efficiency of volume hologram.
In the scanning optical system for laser beam printer, so-called f-0 lens is utilized to provide a scanning spot of constant velocity from deflected light beam having constant angular velocity. Then, f-8 lens is designed to have proper amount of residual distortion. One important point at the optical design of such kind of optical system is to find out the relationship between distortion and point spread function of the lens. In this report, the relationship is made clear by using aberration theory. With some designed examples it is shown that f-8 lens is suitable for scanning purpose, and that the lens makes us highly effective use of laser beam energy by reducing the deformation of point spread function with respect to the deflection angle of beam. As the example of application, the optical elements for semi-conductor laser scanning system are presented.
The derivation of earth relative motion (or "smear rate") in a step-stare spaceborne optical system is presented. Suggested methods of compensating for the smear by focal-plane manipulation are also given. The simulation results of smearing for a 4-hour orbit optical system operating in a step-stare mode (above 45Ã‚Â° North Latitude) are provided.
A concept for near real-time automatic processing of interferometric data from a Laser Unequal Path Interferometer (LUPI) using an EO camera and mini-computer is presented. A major advantage of this system is a straightforward replacement of the standard film camera by an EO camera (with no further modification required to the interferometer). Testing of the optical systems with obstructions and/or spiders and baffles within the aperture is done automatically. The system is designed for implementation in the fabrication/test cycle of ultra-high quality optical components and systems; where averaging is used to reduce random test errors (e.g., vibration and air turbulence). The system is configured as having portable E/O cameras and monitors hooked into ports at various lab facilities via cabling to the mini-computer at the Data Reduction Station. Itek's Optics Package Fringe Reduction (FRED) software is available at the Data Reduction Station for full analysis capability.
The large collimator is designed to test laser tracking systems with apertures as large as 1 m. To reduce the l-m aperture of the large collimator to a reasonable working size, two confocal parabolas (Mersenne) reimage the pupil to 0.1 m with a 1.4-m off-axis parabola decentered 1 m. Near the reimaged pupil two cylindrical mirrors are used to introduce near-field defocus and astigmatism while a two-axis tilt mirror simulates target motion and atmospheric tilts. A second Mersenne reduces the beam size further with the intermediate focus used for far-field atmospheric turbulence and thermal blooming simulation. A bandpass beamsplitter allows the incoming laser beam to proceed to a laser analyzer section, for directional and spot size information, while allowing the infrared radiation from the target to pass to the tracker. A large focal ratio allows for zooming the target by a "trombone" set of movable mirrors and fixed target. Rotation is provided by a K-mirror image rotator. The optics are chilled in a cold box and situated on an optical bench in a van for transportation.
To simulate the wavefront perturbations produced when an optical system moves or scans through a static atmosphere, a rotating phase plate was situated in the vicinity of a focus in a collimator. The phase plate is a mirror with statistically defined deviations from flatness etched into the surface. Its diameter is considerably larger than the collimator clear aperture at that location. The collimator beam is decentered from the rotation axis such that the mirror rotates past the beam and presents a changing wavefront whose appearance to the test optical system resembles atmosphere streaming past the aperture. The computer simulation of the statistical perturbations, fabrication method, interference testing, and computerized reduction of the results to compare with the experimentally observed five-thirds law are discussed.
We have found that reliance on theoretical models or incomplete manufacturers data is not adequate for predicting the result of combining optical and electro-optical components into a system. The complete imaging characteristics of each component must be accurately known if reliable predictions are expected. Inhouse testing then is desirable where possible. Some components have well established evaluation procedures. Others such as coherent fiber optics, require various test techniques some well established and others must be devised if complete characterization is needed. This is especially true where changes in magnification are a feature of the bundle. A description of the techniques we use for testing the MTF, image rotation, magnification, image size variation, distortion, shear, transmission efficiency, transmission variation, transmission defects, flatness and acceptance angle are included in this paper.
The Periscope Optical Test Equipment (POTE) is designed for use with submarine periscopes. The POTE concept provides for a measurement of a specific parameter - rather than a comprehensive analysis - to determine if the periscope optical performance is satisfactory. The system design incorporates custom optics (reflecting the photographic use of submarine periscopes) in conjunction with a microcomputer - based image processor. Special fixturing was designed to allow for rapid installation and alignment aboard a submarine. The use of a single spatial frequency, a programmable criterion level and automatic self-checks are discussed.
Evaluation of the quality of cylindrical optical elements has always presented severe difficulties. Previous techniques have depended on either indirect methods or methods providing relatively poor resolution. A new basic interferometric technique makes possible direct figure characterization for cylindrical optics utilizing conventional interferometric equipment. Several variations are possible for different test conditions for both cylindrical mirrors and cylindrical lenses. This measurement technique has been applied successfully to cylindrical mirrors and lenses. The basic technique and several variations are presented and discussed. Examples of the results of actual tests are included with test conditions specified, and a complete listing of necessary conventional interferometric equipment is given.
Steep domes and nearly hemispherical shells are difficult to test from the center of curvature because of the very wide angle the test piece subtends from that position. To test the whole piece at once would require exceedingly fast f# test optics. A mosaic picture of the whole element can be built up by sequentially looking at subaperture areas, but this is clearly not ideal and is not suited for large-volume production situations. This paper describes a simple double-pass null test for wide-angle concentric domes and shells that greatly reduces the f# speed required of the test optics, and yet fills the whole aperture while giving a perfect null. The test involves an auxiliary Mangin mirror type of element nearly in contact with the dome or shell, and makes use of the aplanatic points of the inner surface of the test piece.
The demand for cylindrical lenses and reflectors with precise surfaces has prompted an investigation into manufacturing techniques which is still underway. The paper describes the findings so far in such areas as curve generation, coarse and fine grinding, and polishing. The effects of various type of generation on subsequent manufacturing processes are also being considered. Inspection techniques for cylindrical surfaces, including test glasses, Foucault tests and performance tests are also being investigated. The design and construction of machinery for the grinding and polishing operations, as well as generating, will be described, giving consideration to the geometry, requirements for rigidity, lack of chatter, types of motion, accuracy required for various processes and differences from conventional spherical grinding. The design and manufacture of grinding tools and laps, as well as the precisions required for various stages will also be discussed.
Instrumentation to detect surface flaws in cartridge cases has been developed for high speed on-line inspection. Scattering of light from a line focused on the case surface indicates the presence of surface flaws and the instrumentation permits rough categorization of flaws into dents and scratches. Two methods of light detection have been implemented, and the purpose of this paper is to compare these techniques. The first technique uses fiber optics to collect the scattered light and carry it to a photomultiplier tube to generate a signal, while the second technique uses solid-state diodes to produce the sig-nal. Angled surfaces such as the shoulder on the cartridge case influence the response of the fiber-optics due to the acceptance cone of the fibers. To circumvent this problem, the fibers must be judiciously positioned during manufacture of the fiber-optic bundles. The solid-state diodes do not have the limited acceptance angle and thus provide more uniform response. However, the diodes require placement of electronics on the rotating exam wheel near the detectors. The processing electronics for-both systems are identical.
A dimensional measuring system, the profile monitor, has been developed to measure part dimensions with a standard deviation of 0.0001 inch at a throughput rate of 1200 parts/ minute. The monitor is one measurement system on an advanced high speed inspection system designed to monitor the production of cartridge cases. The complete system includes a mechanical handler, measurement instruments (which make five measurements), system monitoring instruments and a dedicated minicomputer. This paper describes the profile monitor and its performance. The profile monitor is an electro-optic system that utilizes fiber optics to project an image of the case onto charge-coupled device image sensors. Measurements are made for five different case dimensions: 1) head thickness, 2) head diameter, 3) extractor groove diameter, 4) gas seal length and 5) total length. The profile monitor consists of five major elements: the case gauging fixture, the optical system including an illumination source and folding optics, the diode array (detector), the processing electronics and the computer. Electronics consist of the diode array and driver, thresholding circuit, measurement timing logic and data buffers. The square image conduit (six micron fibers) is structured to take the edges of the projected case image and transfer the image to a 0.125 inch linear charge coupled device (CCD) sensor. Logic is employed to detect the shadowed edges of the case and count the number of elements darkened by the shadow.