This issue of Optical Engineering offers a series of articles highlighting the reduction-to-practice phase which takes place in the development of an optical system. In this issue, optical hardware evolves from system specification to assembly and test. This evolution follows a pattern that has changed little in the past 364 years, when Gallileo first perfected, then used Hans Lippershey's telescope to discover the satellites of Jupiter. While the pattern remains constant, significant changes have occurred in the development of improved tools and techniques. Science and engineering has provided the lens designer with large computers and faster programs, the optician with better machines and optical materials, and the technician with lasers and other sophisticated test equipment in a concerted effort to advance the state of the optical art. The development and application of this more advanced equipment constantly challenges the experience and training of the applied scientist and optical engineer.
On more than one occasion, responsible engineering people have produced specifications for a lens system that are totally unachievable due to either diffraction effects, manufacturing limitations or both. This paper examines several typical examples of perfect and near perfect lenses, showing the magnitude of degradation that must be expected. Evaluation is accomplished first by examining the effect on energy distribution within the Airy Disc pattern. Then, in order to demonstrate the effect on images of extended objects, Modulation Transfer Function data is presented for the same condition. The data indicates that diffiaction at the system aperture, particularly where an obscuration is present, and minute residual wavefront imperfections ( X/4 OPD), will have an effect on the final system performance that must be taken into account. An important factor iri determining the significance of these errors on final system performance would be whether the optics are forming point images or extended images of real world objects.
In this paper we discuss methods for testing and evaluating lenses to determine how well the lens fulfills its designed function over the entire field. The actual image testing system for testing production lenses is described in detail.
The utilization of optical alignment instrumentation in the assembly of certain large telescopes provides a convenient means for installing and calibrating these massive systems in the observatory. An experiment was performed during the factory acceptance test of a 1.22 m (48 in.) aperture Cassegrain to determine the accuracy which might be realized in practice. Scatterplate-interferometry and Hartmann tests were used with a 1.24 m (49 in.) optical flat to quantify laboratory performance. The results were impressive. The telescope alignment not only met the one-quarter wavelength peak-to-peak specification but also demonstrated that this type of calibration procedure can be performed on site, requiring a minimum of time, equipment and operator experience.
This column, which is written as a paper, is the first of a series dealing with subjects of interest to those involved in fabrication and testing. The title of the column will be "Optical Systems Manufacturing Technology," and it will appear regularly in the Forum section of the SPIE-Glass. We would like to solicit comments on the opinions expressed in the column.
Coded aperture imaging of X ray or y ray emitting objects using on-axis Fresnel zone plate apertures was the original method suggested by Mertz in 1961. Since then other forms of coded aperture imaging have become more popular. We show in this paper that, under certain well-defined conditions, high quality images can be obtained with Mertz' original encoding method.
A highly accurate electrical subtraction technique has been developed for detecting and imaging very small periodic contrast changes in a video signal. The process uses two electrical-in electrical-out vidicon-like cathode ray tubes. The first tube puts out a video difference signal only when there is a change in the input video signal. The second, a silicon target storage tube, is used for integrating the difference signal. This storage tube is alternately operated above and below the first crossover point on the secondary emission characteristic for increased common mode rejection in the integrated difference signal. Periodic signals occupying .06 percent of the full scale video scene have been detected. This represents a factor of 10 increase in sensitivity over previously reported results.' The technique has been successfully used for detecting and imaging very small concentrations of non-radioactive iodine and xenon in x-ray phantoms using a conventional television fluoroscopy system. The details of the image subtraction electronics will be described.
At the Laser Laboratory of the Medical Center of the University of Cincinnati for more than 11 years detailed studies have been done with laser surgery in animals and in clinical investigative studies in a large series of patients. It is evident that the optical engineering phase of current laser surgical instrumentation requires considerably more research and development. Reliable high-output lasers, preferably CW, Md-YAG, CO2 are argon are required. Optical engineering requirements include flexibility and efficiency of beam transmission through small, sterilizable precise operating probes capable of incision, coagulation or fulguration. Probes must be adaptable for use with operating microscopes and for laser surgery in body cavities.
Common path interferometry is perhaps less common today with the availability of laser sources, but its usefulness has not been diminished. It offers many advantages in terms of ease of operation under difficult shop environments that may even preclude unequal path interferometry. Since only the classical requirements for coherence length of the light source need be met, conventional arc lamps may be used. The laser still provides a better source since the intensity is generally so much higher than can be obtained with arc lamps that short photographic exposures can be used in obtaining interferograms.
GENERAL REMARKS The heart of every electro-optical device is the radiation detector. It has the function of converting the incident radiation into an electrical signal (voltage or current) which in turn can be amplified, processed, drive displays, and which constitutes a meaningful measure of the incident radiation. The term, detector, usually is applied to a physical device which consists of the radiation transducer itself as well as windows, limiting apertures, possibly electron optics, and cooling units. But the performance of the detector and its capabilities are almost entirely determined by the radiation transducer.