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Star Testing Astronomical Telescopes
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To order this item outside the United Kingdom, please contact us.
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Star Testing Astronomical Telescopes
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| Model / Description |
View in Showroom |
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| Star Testing, 2nd Edition |
yes |
WLBSTAT2 |
£ 40.00 |
£ 6.00 |
24 hours |
| Star Testing, 1st Edition |
yes |
WLBSTAT |
£ 30.00 |
£ 6.00 |
24 hours |
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Outline
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Many observers harbour misgivings about their telescope. The manufacturer may have
guaranteed accuracy to "one-quarter wavelength" or as "diffraction-limited" but most
telescope users have, at best, only a hazy idea of how to personally verifying such
claims. Sure, there are ways to check the accuracy of individual components but for
many they are hard to understand or require costly reference optics and other test
equipment. Besides, telescope users are interested in the performance of the entire
optical train, not just the main optical element.
What is really needed is a test that can be used at the observing site, so that all
the problems that impact on a telescope's performance can be diagnosed. Isn't there
a simpler and more complete way than the complicated shop tests? Yes, the star test
is such a method. It uses the entire working telescope. It is not a poor substitute
or a work-around that uses bits and pieces of the optical system. It is the oldest
and most sensitive of the optical tests—an inspection of the diffraction image itself.
Star-test results apply to the complete imaging performance of the telescope.
The star test is lightning-fast and requires only a good high-power eyepiece.
It tests the telescope for precisely what it was meant to do. Bad or poorly-aligned
instruments fail the star test unambiguously. The star test often allows you to correct
the optical difficulty immediately in the field, when you might be frantic to have your
telescope perform well to observe a once in a lifetime event.
While the star test has been around for centuries learning it has often been hampered
by messy mathematics and its visual nature. Most people who use it have learned it at
the elbow of a patient Master. In this book, Dick Suiter becomes your Master. He carefully
shields you from difficult diffraction theory and uses advanced computer generated graphics
to show you the appearance of each aberration. Again and again, you will look at Dick's
graphics and say "I've seen that before. So that's what it was!" The star test is a powerful
but inexpensive way of obtaining better resolution and contrast. With this book most
observers will find that they don't need a new telescope because they now can test, diagnose
and fix the one they have. Using Star Testing Astronomical Telescopes as a guide, your telescope
will perform to the best of it's abilities and perhaps it will show images better than you would
have believed possible.
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From The Reviewers
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Tonight’s the night. That $800 telescope you’ve been waiting for has finally arrived.
After excitedly setting it up, you centre Jupiter in the eyepiece. Excitement builds.
You focus and focus again, switch eyepieces, focus again. The view is horrendous!
What’s causing it? Is it just unstable atmospheric conditions or are the telescope’s
optics out of alignment? Is it heat rising off the asphalt parking lot you’re observing
on or is the telescope too warm? Or, horror of horrors—could it be that your new mirror
is not up to specifications? And what kind of flaw is it? Rough surface? Spherical aberration?
Astigmatism?
Far too many of us have experienced this disturbing scenario. But now, thanks to Star Testing,
you can answer these questions easily and probably have the telescope operating in no time.
And if there is an optical problem, you will be able to communicate it clearly to the dealer
and get prompt action.
Chapter One and Two explain basic optics in a fashion that any motivated beginner can follow.
Computer-generated illustrations of defocused star images are so realistic that you can learn
a great deal by just looking at the pictures . . . Star Testing is bound to have a big impact
on our hobby. Harold Suiter wants to help buyers assess optical quality so that it plays a
larger role in purchasing decisions. This, he feels, will give manufacturers added incentive
to produce superior products. In my opinion Suiter will succeed—if enough of us buy this book
and read it. Its cost is a small price to pay for becoming an informed consumer.
Astronomy magazine
"I’m going to tell you a little-known fact," begins Harold Richard Suiter in his new book . . .
"Telescopes are easy to test." It’s true. The hard part for most amateurs has been finding out
exactly how to do it . . . Now, at last, Suiter has analyzed the star test in book-length
thoroughness. He presents a bounty of information and instruction in a clear, practical manner
never before available . . . The book displays with perfect clarity all the star test comparison
images you’ll ever need, illustrating all kinds of telescope aberrations in their pure forms . . .
Those are just highlights of this long overdue book. It quantifies almost all the effects it
discusses, presents modulation-transfer functions indicating how they affect different types of
observing, delves into diffraction theory, and yet is full of advice and experience from real-world
amateurdom.
Sky & Telescope magazine
It is very rare to find a book that has such an immediate appeal to the telescope maker,
observational astronomer, and theoretical physicist….A first casual inspection of the book
indicates that it should reside on the applied optics book shelf of a Physics Department library.
Nothing could be further from the truth. Suiter, who is an experimental physicist, has been very
successful in using everyday analogies to explain the fundamentals of diffraction optics. There
is a great deal of good practical information for those readers prepared to persevere. For those with
a more than casual approach to their telescopes, this book will become in the widest sense,
a benchmark in astronomical telescope testing literature. Most importantly, it will give some weight
to increasing the quality assurance standards of commercial telescopes, from the viewpoint of a better
informed user.
Southern Stars
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Some Examples
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Testing your optics to confirm quality is obvious. What is less straightforward is
the way of testing. Telescope makers can use a variety of techniques, but ordinary
telescope users find that learning a workshop method is difficult. They have only
one mirror that doesn't change, so it is easier to test it on the sky. The star
test is a good way of evaluating instruments for one-time users.
You must be careful to test the instrument when it has cooled off and is under fairly
tranquil skies, as the following spherical aberration with strong turbulence figure shows.
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The following aberration types figure shows some common difficulties with telescope optics.
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Table of Contents
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Foreword
An Introduction to the Author
Preface
1. Introduction
1.1. Telescope Evaluation
1.2. Testing the Surfaces
1.2.1. Sources of Errors
1.2.2. Measures of Optical Quality
1.3. The Star Test—A Brief Overview
1.3.1. Diffraction Rings
1.4. The Reason for Star Testing
2. An Abbreviated Star-Test Manual
2.1. Some Necessary Preliminaries
2.2. Optical Problems in Turn
2.2.1. Secondary Mirror Obstruction
2.2.2. Misalignment
2.2.3. Atmospheric Motion and Turbulence
2.2.4. Tube Currents
2.2.5. Pinched or Deformed Optics
2.2.6. Spherical Aberration
2.2.7. Rough Surfaces
2.2.8. Zonal Aberrations
2.2.9. Turned Edges
2.2.10. Astigmatism
2.3. Concluding Remarks
3. Telescopes Are Filters
3.1. Perceptions of Reality
3.2. A Comparison to Audio
3.2.1. Aperture Diameter/Size of Speakers
3.2.2. Colored Filters/Equalizer Filters
3.2.3. Image Processing/Signal Processing
3.2.4. 3.2.4 Scattered Light/Audio Noise
3.2.5. Spatial Frequency/Audio Frequency Responses
3.3. The Modulation Transfer Function (MTF)
3.4. The MTF in Use
3.4.1. MTF Associated with Defocusing
3.4.2. Stacking of MTFs
4. Diffraction
4.1. The Coordinates of Light
4.2. The Consequence of Filtering
4.3. Waves Are Reborn
4.3.1. Diffraction and Focusing
4.3.2. Fresnel Zones
4.3.3. Fresnel Zones with Defocus
4.4. Nodes and Antinodes
4.5. Other Aberrations—The Pupil Function
5. Conducting the Star Test
5.1. Defocusing and Sensitivity
5.1.1. Focuser Motion Related to Defocusing Aberration
5.1.2. Sensitivity of the Star Test
5.2. Artificial Sources
5.2.1. Distance of Artificial Sources
5.2.2. Diameter of Artificial Sources
5.2.3. Using a Reflective Sphere Instead of a Pinhole
5.2.4. Setting Up a Nighttime Artificial Source
5.3. Performing the Test
5.3.1. 8-Inch f/6 Newtonian Reflector
5.3.2. 16-Inch f/4 Dobson-mounted Newtonian
5.3.3. 6-Inch f/12 Apochromatic Refractor
5.3.4. 8-Inch f/10 Schmidt-Cassegrain Catadioptric
6. Misalignment
6.1. Kinematic View of Alignment
6.2. Effects of Misalignment
6.3. The Aberration Function of the Misaligned Newtonian
6.4. Filtration of a Misaligned Newtonian
6.5. Aligning Three Telescopes
6.5.1. The Newtonian Reflector
6.5.2. The Refractor
6.5.3. The Schmidt-Cassegrain
7. Air Turbulence and Tube Currents
7.1. Air As a Refractive Medium
7.2. Turbulence
7.2.1. The Aberration Function
7.2.2. Filtering Caused by Turbulence
7.2.3. Observing Turbulence
7.2.4. Corrective Action
7.3. Tube Currents
7.3.1. The Aberration Function
7.3.2. Filtering of Tube Currents
7.3.3. Observing Tube Currents
7.3.4. Corrective Actions for Tube Currents
8. Pinched and Deformed Optics
8.1. Causes
8.2. The Aberration Function
8.3. Filtering of Pinched Optics
8.4. Diffraction Patterns of Pinched Optics
8.5. Fixing the Problem
9. Obstruction and Shading
9.1. Central Obstruction
9.2. Spider Diffraction
9.3. Shading or Apodization
9.4. Dust and Scratches on the Optics
10. Spherical Aberration
10.1. What Is Spherical Aberration?
10.2. The Hubble Space Telescope
10.3. Generalized Spherical Aberration
10.4. The Aberration Functions
10.5. Correction Error (Lower-Order Spherical Aberration)
10.5.1. Filtering of Spherical Aberration
10.5.2. Star-Test Patterns of Correction Error
10.5.3. Estimation of the Severity of the Problem
10.6. Testing for Correction
10.7. Higher-Order Spherical Aberration
10.7.1. Star-Test Patterns of Higher-Order Spherical Aberration
10.7.2. Filtering of Higher-Order Spherical Aberration
10.8. A Compact, Uniform Standard for Optical Quality
10.9. Tolerable Errors
11. Circular Zones and Turned Edges
11.1. Causes of Zonal Defects
11.2. Interior Zones
11.2.1. Aberration Function of S-Zones
11.2.2. Filtering of S-Zones
11.2.3. Detecting Interior Zones in the Star Test
11.3. Turned Edges
11.3.1. Aberration Function
11.3.2. MTF of Turned Edge
11.3.3. Image Pattern of Turned-Down Edge
11.3.4. Signal-to-Noise Ratio of a Turned Edge
11.3.5. The Width of the Turned Edge
11.3.6. Remedies for Turned Edge
12. Chromatic Aberration
12.1. Dispersion
12.2. The Achromatic Lens
12.3. Residual Chromatic Aberration
12.4. The Apochromat
12.5. Testing Refractors for Other Aberrations
12.6. The Star Test for Chromatic Effects
12.6.1. Wedge, Assembly Errors, and Atmospheric Spectra
12.6.2. Star Test for Conventional Astronomical Visual Doublets
12.6.3. Star Test of Apochromats or Advanced Refractors
12.6.4. Chromatic Effects in the Eye
12.6.5. The Eyepiece
12.7. Conclusions and Remedies
13. Roughness
13.1. Roughness Scales and Effects
13.2. The Terminology of Roughness
13.3. Medium-Scale Roughness, or Primary Ripple
13.3.1. The Aberration Function of Medium-Scale Roughness
13.3.2. Filtering Effects of Medium-Scale Roughness
13.3.3. Star Test on Medium-Scale Roughness
13.3.4. Roughness and Turbulence
13.4. Small-Scale Roughness, or Microripple
13.4.1. The Aberration Function of Small-Scale Roughness
13.4.2. Filtering of Small-Scale Roughness
13.4.3. The Great Unknown
14. Astigmatism
14.1. Astigmatism in Eyes and Telescope Optics
14.2. Causes of Astigmatism
14.3. Aberration Function of Astigmatism
14.4. Filtering of Astigmatism
14.5. Star-Test Patterns
14.6. Identification in Newtonian Reflectors
14.7. Refractors or Schmidt-Cassegrains
14.8. Remedies
15. Accumulated Optical Problems
15.1. Breaking the Camel's Back
15.2. Fixing the Telescope
15.3. Errors on the Glass
15.4. Testing Other Telescopes
15.5. When Everything Goes Right
A. Other Tests
A.1. The Foucault Test
A.2. The Hartmann Test
A.3. Resolution of Double Stars
A.4. Geometric Ronchi Test
A.5. Interferometry
A.6. How Do Interferometers Work?
A.7. The Point-Diffraction Interferometer
A.8. The Null Test
B. Calculation Methods
B.1. Diffraction Concepts
B.2. The Fraunhofer and Fresnel Approximations
B.3. Image Calculations for Symmetric Apertures
B.4. Image Calculations for Nonsymmetric Apertures
B.5. The Programs
B.5.1. Symmetric Pupil Function
B5.2. Asymmetric Pupil Function
B.6. Verification of Numerical Procedure
B.6.1. Comparison of APERTURE and ASYMM
B.6.2. A Numerical Comparison with an Analytic Solution
B.6.3. Comparison with Published Patterns
B.7. Numerical Limitations on Programs
B.8. Difficulties in Printing
C. Minor Axis and Offset Derivation
C.1. Derivation
C.2. Test Case
C.3. Approximations
D. Labeling of Diffraction Patterns
E. Eyepiece Travel and Defocusing Aberration
F. Glitter in a Shiny Sphere
G. List of Common Symbols
Glossary
Bibliography
Index
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Notice
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We are constantly checking the accuracy of the technical data. We are prepared to provide
more detailed information on request. Technical data is subject to change without notice.
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Opticstar Showroom
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Opening Hours
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updated: 2nd January 2013
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We are closed on Sundays and public holidays.
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Download the Opticstar imaging catalogue here.
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updated: 25th March 2009
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Read the latest review about the A&M 152mm f/8 A&M/TMB on
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According to the review this telescope combines the "beauty of a Ferrari" with
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