Zemax in general

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Optical Systems Design

with ZemaxLecture 1


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February 18, 2014 Optical Systems Design 2

Why Optical Systems Design

Optical system design is no longer a skill

reserved for a few professionals. With

readily available commercial optical design

software, these tools are accessible to thegeneral optical engineering community and

rudimentary skills in optical design are now

expected by a wide range of industries who

utilize optics in their products.


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Course Aims

To introduce the design principles oflens and mirror optical systems andthe evaluation of designs using

modern computer techniques. Thelectures will cover lens design,

aberrations, optimization,tolerancing and image quality

metrics.


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ZEMAX

The ZEMAX Optical Design Program is a

comprehensive software tool. It integrates

all the features required to conceptualize,

design, optimize, analyze, tolerance, anddocument virtually any optical system. It is

widely used in the optics industry as a

standard design tool. This course will

introduce the basics of ZEMAX.


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Other Optical Design

Software!Code-V (Optical Research Associates)

!OSLO (Sinclair Optics)

!OpTaliX (Optenso Ltd)

!ASAP (Breault Research)

!TracePro (Lambda Research)

!

FRED (Photon Engineering)



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Local Experts

! Jurgen Schmoll

! Stephen Rolt

!Colin Dunlop

!Tim Morris


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Course Outline

! Lecture 1: Introduction

! Lecture 2: Sequential Systems

!

Lecture 3: Optimization! Lecture 4: Tolerancing

! Lecture 5: Non-sequential & other stuff

Web page: http://astro.dur.ac.uk/~rsharp/opticaldesign.html


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Objectives: Lecture 1

At the end of this lecture you should:1.

Be able to install a version of the Zemax opticaldesign programme on a Windows PC

2. Understand the main tasks involved in optical

systems design with Zemax3.

Be aware of Zemax notation for the 5 mainSeidel aberrations

4. Know the relevance of the terms: optical axis,

stop, pupil, chief ray, marginal ray, point spread

function for Zemax5. Use the Zemax lens data editor to enter the

specifications of a simple lens


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Getting started

!

Download a copy of Zemax fromhttp://www.radiantzemax.com

! CfAI/Atmol members can use the sharedlicense server onzemax.cfai.local. This

requires a copy of the filesntlconfig.xmlfromthe server Exchange/installers/Zemax to becopied into the main Zemax directory (C:\Program Files\Zemax)

!Fivelicences are available. See who is using

them at http://zemax.cfai.local:7002! Non-CfAI/Atmol members should use the

Zemax demo


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Recommended Texts

! Zemax manual

! Introduction to Lens Design with Practical ZemaxExamples, Joseph M Geary (Willmann-Bell Inc.)

! Optical Systems Design, Robert Fischer & Bijana

Tadic(SPIE Press)!

Practical Computer-Aided Design, GregoryHallock-Smith (Willmann-Bell Inc.)

!Astronomical Optics, Dan Schroeder (AcademicPress; GoogleBooks)

!

Optics, Jeff Hecht (Addison Wesley)

Also the Zemax knowledge basehttp://kb-en.radiantzemax.com/Knowledgebase/


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Optical Systems Design

Science or art of developing optical systems toimage, direct, analyse or measure light.

!

Includes camera lenses, telescopes, microscopes,

scanners, photometers, spectrographs,

interferometers, ! Systems should be as free from geometrical optical

errors (aberrations) as possible.

! Correcting and controlling aberrations is one of the

main tasks of the optical designer (includes

performance evaluation and fabrication/tolerancing

issues).


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Historical Note! Lens design has changed significantly since

~1960 with the introduction of digital computersand numerical optimisation.

! Equations describing aberrations of lens/mirrorsystems are very non-linear functions of systemparameters (curvatures, spacings, refractive

indices, dispersions, )!

Only a few specialised systems can be derivedanalytically in exact closed-form solutions.

! Analytical design methods (Petzval, Seidel) werehistorically based on a mathematical treatmentof geometrical imagery and primary aberrations

still useful for initial designs.

! Numerical evaluation methods ray trace manylight rays from object to image space.


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Seidel (3rdorder) Aberrations

1. Spherical aberration

2. Coma

3. Astigmatism

4. Field curvature

5. Distortion

6.

Longitudinal chromatic aberration7. Lateral chromatic aberration


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Numerical Evaluation Methods

! Assume only trigonometry, law of reflection andSnells law

!

! For each ray calculate new ray parameters at

each surface!

Sequential ray-tracing assumes that light travelsfrom surface to surface in adefined order.

! Non-sequential ray-tracing does not assume apre-defined path for the rays, but when a ray hits

a surface in its path, it may then reflect, refract,diffract, scatter or split into child rays (scatteredlight).

n1sin"

1= n

2sin"

2


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Numerical OptimisationMethods

!Given a starting configuration, thecomputer can be used to optimise adesign by an iterativeprocess.

!Final image quality is best that can be

achieved under constraints of basicconfiguration, required focal length, f/number, field of view, wavelength etc.

!Programs are still dumb. Designer must

supply intelligence through selection ofstarting configuration, control ofoptimization parameters, understandingof underlying optical theory, etc.


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Objects, Light Rays &Wavefronts

! Objects composed of self-luminous (radiant) points oflight

!

Trajectories of photons from each of these points

define the light rays

!

Neglecting diffraction, these physical rays becomegeometrical rays (ray bundles)

! Wavefronts are surfaces normal to rays

! Light travel times along all rays to the wavefront from

an object point are the same (for a fixed

wavelength)!

Neglecting diffraction, physical wavefronts becomegeometrical wavefronts (good approximation

except near boundaries or edges)


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Objects, Light Rays &Wavefronts


ObjectPlane

ImagePlane

Optical axisWavefronts

Ray bundles


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The Optical Axis

! Most optical systems are collections ofrotationally symmetric surfaces whose centres of

curvature are all located along a common axis

(Optical Axis)

!

Plane surfaces have infinite radius of curvature! Intersection of the optical axis and a surface is at

thesurface vertex

! Longitudinal cross-section defines a meridionalplane (all equivalent)

!

Ray in this plane are meridional rays. Rays out of

plane areskew rays.


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Stops & Pupils

! Every optical system contains one physical aperture that

limits the extent of the wavefront for the ray bundle which is

transmitted through the system to the on-axis image point(aperture stop orstop)

!

If optics are large enough then this will also be true for off-axisimage points

! In many cases this is not true leading to mechanical

vignettingof off-axis image points

! Size and location of the aperture stop can have important

impact on system performance through its effects on

geometrical aberrations

!

Image of the stop in object space is the entrance pupil.Image of the stop in image space is the exit pupil.

! Focal ratio (e.g. f/5.6) is ratio of focal length (for object at ")

to entrance pupil diameter (EPD)


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Stops & Pupils


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Marginal & Chief Rays

!Marginal ray originates at the object point on axisand goes to the edge of the stop of the system.

! Chief ray (principal ray) originates at the object

point at the edge of the field of view and passesthrough the centre of the stop of the system.

Axial height (transverse distance away from the

optical axis) of the marginal ray is zero at the object

and all images of the object. At these locations the

axial height of the chief ray determines the size

(semi-diameter) of the object and its images(magnification). These roles are reversed when

considering the aperture stop and its images (pupils).


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Marginal & Chief Rays


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Point Spread Function (PSF)

!Impossible to image a point object asa perfect point image.

!PSF gives the physically correct light

distribution in the image planeincluding the effects of aberrationsand diffraction.

!

Errors are introduced by design(geometrical aberrations), optical andmechanical fabrication & alignment.


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Co-ordinate Systems andSign Conventions

!No standardization betweendifferent codes!

!Zemax uses a right-handed

cartesian co-ordinate system, wherethe Z-axis is the optical axis and lightinitially moves in the direction of +Z.

!Co-ordinate breaks (rotations) aredefined in a right-handed sense.



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Optical Prescriptions

!An optical design is described by a set ofsurfaces through which the light passes

sequentially.

!

Surfaces are tabulated in the lens dataeditor and are numbered sequentiallyfrom the object surface (surface 0) and

ending with the image surface.

!A minimum of 3 surfaces is required

(object, stop, image).



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Surface Parameters

!Surface number

!Radius of curvature

!Thickness to the next surface

!

Glass type in the next medium!Aspheric data (if any)

!Aperture size (semi-diameter)

!Tilt and decenter data (if any)

One surface is designated the stop surface.



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Using the Lens Data Editor

!Gen button: define entrance aperture

!Fie button: define field angles (FoV)

!Wav button: define wavelengths

!

Singlet lens prescription:

R1 = 100 mm, t1 = 10 mm, Glass = BK7, Semi-D1 = 25 mm

R2 = -100 mm, t2 = Quick-focus, Air, Semi-D2 = 25 mm

An aperture stop (entrance pupil) is placed at the 1st

lens surface (D = 40 mm).


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ZEMAX Lens Data Editor



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First Order Properties



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Summary: Lecture 1

!Optical design has changed radicallysince the introduction of modern ray-

tracing software packages

!ZEMAX is a comprehensive software tool

which integrates all the features requiredto design an optical system

!The optical design process involvesdeveloping a conceptual optial design,

ray-tracing an optical layout and varyingparameters of the specification to

improve performance


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Exercises: Lecture 1

!Install Zemax (or the Zemax demo)on your PC

!Use the lens data editor to input the

optical prescription of the biconvexsinglet from the lecture

!Investigate how the focus dependson wavelength and lens curvatures

!

Investigate how the image qualitydepends on the thickness of the lens


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