Berlyn Brixner

Refractive-Index Interpolation for Fused Silica*

The advantages of a four-term Sellmeier-equation fit to refractive indexes of recently produced fused silica are described. The four-term fit gives more accurate smoothing and interpolation of data than the three-term fit used previously and also indicates data of questionable accuracy. After the suspect data had been eliminated, fits with an average deviation of 4.3 · 10−6 were obtained with both three- and four-term equations over the range 0.21–2.32 μ.

Automatic Lens Design for Nonexperts

Automatic lens design by nonexperts is practical with the 1962 LASL lens-designing code, a general-purpose iterative program for evaluating and designing optical lens and mirror systems with surfaces generated by conic sections. Using skew ray traces, it analyzes lens performance statistically, finds differences resulting from design-parameter alterations, and computes a linear combination which will1, improve performance. Program characteristics, lens parameters, ray sampling, image evaluation, lens-performance weights, merit calculation, and parameter interactions are briefly described. Sample calculations are given in detail for a Lister-type lens and in summary for a special-purpose zoom lens.

Lens design merit functions: rms image spot size and rms optical path difference

The chief lens design problem is to get all the optical paths from object point to image point equal within a small fraction of a wavelength to ensure that spherical wavefronts will be converging on all image points in the field of view. The LASL lens design program minimizes the lateral deviations of the rays from their ideal image points. Results given here show that this procedure also minimizes the optical path difference and that there is a linear relationship between the rms image spot size and the rms optical path difference.

Optimization of a 4-m Asymmetric Czerny–Turner Spectrograph*

The properties of a 4-m plane-grating Czerny–Turner spectrograph have been analyzed by tracing rays through the spectrograph. Contrary to results recently reported by Chandler in this journal, it was found that the optimum position of the grating is near that predicted by the Fastie–Rosendahl analytical expression. It is also shown that the image width can be made small all the way across a 50-cm plate, that the focal curve can be made straight, and that a position of the entrance slit can be found that makes it unnecessary to refocus the spectrograph when the grating is rotated.

Lens design and local minima

The widespread belief that local minima exist in the least squares lens-design error function is not confirmed by the Los Alamos Scientific Laboratory (LASL) optimization program. LASL finds the optimum-minimum region, which is characterized by small parameter gradients of similar size, small performance improvement per iteration, and many designs that give similar performance. Local minima and unique prescriptions have not been found in many-parameter problems. The reason for these absences is that image errors caused by a change in one parameter can be compensated by changes in the remaining parameters. False local minima have been found, and four cases are discussed.

Faster LASL Lens Design Program

The following improvements have made the LASL lens design system much faster, though less versatile, and have maintained the calculation accuracy: an increment-vector damping technique optimized by a search procedure, analytic differentiation, simultaneous design on all variables, reliable convergence criteria, vignette control by biased violation errors, bounds for the variables, and an enlarged weighting procedure. The designing system optimizes the sizes and positions of many-ray image spots without consideringthe classical aberrations. As a sample problem the symposium lens has been redesigned.

One Million Frame per Second Camera

The design and construction of a 1 000 000 fps (frame per second) rotating mirror frame camera is described. Twenty five consecutive pictures 20 mm in diameter can be obtained on a strip of 35 mm film. A resolution of at least 20 lines/mm is obtained on a moderately fast film like Linagraph Shellburst. Accurate synchronization of the event to be photographed is required. The camera has been most useful in the investigation of explosive and related phenomena.

High‐Speed Turbine‐Driven Rotating Mirrors: Notes on Design, Construction, and Performance

Described in detail are the main features of design and fabrication which contribute to the production of the reliable long‐lived drives of several styles of high‐speed turbine‐driven rotating mirrors. The subjects analyzed are steel mirror fabrication, which includes heat treatment; mirror balancing and surface finishing techniques; important bearing design features; construction of the turbine; and performance of selected models.

Rotating Steel Mirrors—Failure and Success

Four main causes of rotating steel mirror failure—excessive vibration, excessive speed, hydrogen embrittlement, and defective steel—are discussed and illustrated. Performance characteristics are given for a successful, 10 000 rps, 25×38 mm mirror drive.

Optimization to create a four-element laser scan lens from a five-element design

The procedure followed in optimizing a five-element diffraction- limited laser scan lens to eliminate one of the elements is described. The starting procedure uses thicknesses found in the five-element design except for the two central positive elements, which are combined to make a single thick third element. The resulting four-element lens employs high-index glass for each element and achieves diffraction-limited performance.