H. Sun — Lens Design (2016)

Автор: H. Sun
Название книги: Lens Design
Формат: PDF
Жанр: Физика
Страницы: 374
Качество: Изначально компьютерное, E-book

A Practical Guide to Lens Design focuses on the very detailed practical process of lens design. Every step from setup specifications to finalizing the design for production is discussed in a straight forward, tangible way. Design examples of several widely used modern lenses are provided. Optics basics are introduced and basic functions of Zemax are described. Zemax will be used throughout the book.

Lens design is the technique to find the minimum of a nonlinear equation with tens
to hundreds of variables and tens of restriction conditions. Mathematically, such an
equation does not have an analytical solution, and even a numerical solution can be
extremely hard to find. Before the invention of computers, lens design was a daunting
task and the preserve of a few well-educated and highly experienced experts. It often
took hours of hard work to vary the surface profiles and positions of several lenses in
order to focus one ray to a desired point. The fast computing speed of modern computers
and the development of several commercial lens design software dramatically
simplified the lens design process. Nowadays, even those scientists or engineers who
are not major in optics can try to design some simple lenses.
When the lens to be designed is simple, say containing a few elements, a lens
design software can be used to find the true minimum of the equation, we call such
a minimum global minimum, and the design result can be the best possible, even the
designer does not have a lot of optics knowledge. If the lens is complex, say containing
more than 10 elements, a clear global minimum may even not exist, instead several
similar minima may exist. That means there are several designs of equal quality.
Sometimes, a lens design software status can trap in a local “valley” and only find a
local minimum, which is much larger than many other existing minima. Such a design
result is not good. A lens designer needs to determine based on his/her knowledge and
experience whether the design result is reasonably good. If not, he/she needs to manually
change some selected parameters to mathematically move the design status out of
the local valley so that the software can start a new search for a minimum.
For a system with hundreds of variables, a pure scientific accurate evaluation of
the design is often not realistic. Some kind of feeling or “art” needs to be involved
to evaluate the design, as pointed out by some well-known lens designers. The lens
designer’s caliper can make a difference here. The knowledge base of a good lens
designer should include two parts:
1. A sound understanding of optics as expected by everyone.
2. A lot of experience of dealing with the problems occurring during the
design process and manipulating the lens design software to get around the
obstacles encountered. This knowledge is beyond an optics textbook and a
lens design software manual can provide, and can be learned only through
extensive design practice.
It’s not surprising to find that some optical engineers, who have graduated from
top optical schools, cannot effectively design a lens, because they don’t have the
knowledge, which means a lot of design experience. On the other hand, in this
author’s opinion, based on his 15 years of experience as a full-time lens designer,
one can design good quality lenses even without mastering the complex optical aberration
theory. Anyone with a college-level optics knowledge can reasonably design
lenses well as long as he/she has certain design experience, because the increasingly powerful lens design software can solve most of the optics problems encountered
during the design process.
About 10 well-written lens design books have been published now. All these books
emphasize on the part one (knowledge base: optics principle, particularly the aberration
theory) and relatively less on the part two (knowledge base: the very practical
details of design process). Many design examples are given in these books, but often
limited to the design of these well-known classic lenses with only a few elements.
Some of these books were first published more than 20 years ago and understandably
do not discuss the use of lens design software in detail. Some books are textbooks with
many problems for students to solve and to prove the optical principles. Some of these
books are reference books for already experienced lens designers. All these books
are good books, particularly for optical professionals or future optical professionals.
The unique characteristic of Lens Design: A Practical Guide is that it focuses on
the very practical detail process of lens design including how to run the design software,
Zemax. Every step from setup lens specifications at the beginning to finalize
the design for production is discussed in a straightforward way. Designs of several
types widely used modern lenses are discussed. The basic optics is only briefly introduced
in this book. Compared with most other lens design books, this book has a
smaller and concise content, and is relatively easier to read.
Several commercial lens design software are commonly used. They are Code V,
Zemax, ASAP, OSLO etc. Among these, Zemax is probably the most widely used,
because Zemax is an entry-level software, relatively easier to learn, and its price is
relatively low. It is also the personal preference of the author. In this author’s experience,
Zemax is adequate for most lens designs. There is no apparent difference in
optimization power, speed etc. among these lens design software. Therefore, Zemax
is used through this book. The current version of Zemax is OpticStudio 15.5. Zemax
updates the software every few months with some new functions added in and occasionally
with some existing functions being rendered obsolete. All these changes
are progressive and relatively minor. So, once we are familiar with one version of
Zemax, we should be able to run the later version without much difficulties. In this
book, we use italics to denote many terms in Zemax used for special purpose.
The Zemax manual has a large content and is written with a focus on rigorous following
of instructions. A new lens designer may feel lost when reading the manual.
On the other hand, most lens design books do not teach how to use Zemax to design
a lens. Another purpose of this book is to bridge the gap between Zemax manual
and lens design books. The functions of Zemax are often introduced during a lens
design process. Only the main functions of Zemax relevant to specific design steps
are explained. Some useful functions that can easily be overlooked are explained.
Readers of this book learn lens design and Zemax at the same time in a gradual way
and may feel lens design is not difficult.
The author hopes this book can help readers, even those who have not opted for a
major in optics, and help them rapidly gain lens design skill in a short period of time.
Those readers, who don’t intend to become professional lens designers, but want to
occasionally design some lenses for own use, will find this book useful, since the cost of
hiring a lens design consultant is a couple of hundred dollars per hour and on the whole
the cost of designing and tolerancing a lens can often be tens of thousands of dollars.