Lens design: then (1964) and now (1996) by Bruce H. Walker
K_Kz8qV.? "`V:4uz Much has been said and written about the changes to the lens design process over the recent decades. Having worked in this field for the past 30+ years, I have enjoyed being involved with many of those changes. This paper will share some general observations on the subject, and then quantify the impact of those changes by review of a specific lens design first executed in 1964 and then updated in 1996 by application of today's technology.
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bpa^ The lens design process
_=K\E0I.m Typically, the lens design process begins with a set of
optical specifications describing a lens that must meet an established set of performance criteria. Next, the lens designer calls upon personal experience, along with that of others, to identify an existing lens form that has the potential of meeting those specifications with a minimum of modification. This starting lens form is then manipulated by the lens designer, in an effort to make it conform to the established optical specifications. Key to this lens optimization stage are the tools used by the lens designer in the process. Typically, there are three basic tools involved: the computer (hardware), the lens design program (software), and the skill of the designer. All three are essentialno one is more important than the others. The final phase of the lens design process is the unambiguous documentation of the final lens prescription (suitable for manufacture), and of the optical performance that can be expected of the final design.
bwK1XlfD.s :n OCs Hardware and software
C_ W%]8u While the experience and skill of the lens designer is difficult to quantify, improvements in hardware and software over the past 30 years have been vast, and are easily identified. Each lens designer who has worked in the field during these years has followed a path somewhat different from that of his or her colleagues. While typical may not be the best term, I believe my experience accurately reflects many of the changes that have occurred during this time period. Prior to establishing an engineering consulting business in 1991, I had worked for three companies, each involved in a unique aspect of the
optics industry. Initially my lens design work was accomplished using a small (that meant it all fit into the same room) IBM-1620 computer, with a rudimentary software package provided by the computer manufacturer Later, I would work using a computer terminal, connected via phone lines, time sharing a large remote computer, with an optical design software package (ACCOS) installed on that computer. Around 1980 this changed to an arrangement where an in-house minicomputer was available, to be used with a leased software package (CODE IV). Today, I work with a Pentium PC, and have installed on that computer a reasonably priced lens design and optical engineering software package1, which meets all of my optical engineering and lens design requirements.
gWl49' S>+ :m0 pm@ h$d`Jmaq While attempts at cost and speed of computing comparisons are possible, I feel they have lost much of their relevance in recent years. Suffice it to say that the speed with which calculations are now executed far outstrips the designers ability to keep up with the volume of useful data output. Likewise with cost of computing, the speed with which solutions and data are generated, the bargain prices of today's hardware, and the cost of today's typical optical design software package, make the overall cost of computing (in most cases) trivial when compared with the fees being earned by the competent optical designer. Hats off to everyone involved in bringing about this spectacular revolution. Not only have they made all of us better designers and engineers, they have made our lives and work easier and a lot more fun.
POQ4&ChA A typical example
G)gPL]C0 I would like to illustrate a few of the changes that have occurred over the past 30 years by taking a single lens design, one that I was responsible for in 1964, and describing how that design was generated. Recently, I have restored this design, evaluated its image quality, and examined the potential for its improvement by application of today's tools and techniques.
{3 BWT (r-PkfXvIf Early in 1964 I was presented with a request for a lens design that would meet the following specifications:
|~+bbN|b gb26Y!7% Effective focal length (EFL): 260 mm
;O uu+#s Aperture: f/3.0
] YUst]gu3 Image size: 25-mm dia. (5.5-deg field-of-view)
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v~ Wavelength: 1.06 µm (laser energy)
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