"Možda su crne tačke bile ptice u letu..." (Maybe the black dots were birds in flight)

Notes on
AMATEUR TELESCOPE OPTICS

On an early autumn day of 1608, Hans Lipperhey, a spectacle maker from Middelburg, in the Netherlands' coastal province of Zeeland, applied before the States General of The Hague for a patent on an "instrument for seeing far". By that time, use of small rounded glass disks to aid the natural eyesight wasn't new. Those bulging out on both sides, resembling lentil - or "lens" in Latin - have been used to correct for farsightedness since the mid 13th century. The idea of a device for magnifying distant objects may have been already grasped for some time as well. But this was the beginning of something else. In the summer of 1609, Galileo, Harriot, and others, turned the new Dutch invention - the "spyglass" - toward the night sky. The telescope was born.

This tale grew old, but our fascination with telescopes has not. Following text is an attempt to give more of an insight into their inner workings. More specifically, how do they form images and what factors determine their quality. Somewhat unusual, the main aspect is that of the optical wavefront, as opposed to the geometric (ray) "interface". That deliberate choice, while perhaps somewhat less convenient, allows for more accurate qualitative assessment, and should throw more light at the underlying physical fundamentals. Main reference sources are as follows: (1) Astronomical Optics, Daniel J. Schroeder, (2) Aberration Theory Made Simple, Virendra N. Mahajan, (3) Optical Imaging and Aberrations I and II, Virendra N. Mahajan, (4) Optics, Eugene Hecht, and (5) Telescope Optics, Harrie Rutten and Martin van Venrooij. Most of raytracing plots and routine checkups are by ATMOS, Massimo Riccardi, and OSLO, Sinclair Optics. Most of diffraction patterns were generated by Aberrator, Cor Berrevoets.

For additional reading, see extensive coverage of telescope optics and related subjects at Bruce MacEvoy's Astronomical optics

TABLE OF CONTENTS:

 1. IMAGE FORMATION IN A TELESCOPE
Rays and waves  Diffraction  PSF
1.2. Reflection and refraction
1.3. Optical system of a telescope
1.3.1 Gaussian approximation

2. TELESCOPE FUNCTIONS
2.1. Light grasp 
2.2. Resolution
2.3. Magnification

3. TELESCOPE ABERRATIONS: Types, causes
3.1. Wavefront aberrations
3.2. Ray (geometric) aberrations
3.3. Conics and aberrations 2
3.4. Terms and conventions
3.5. Aberration function Seidel Zernike 2 3

4. INTRINSIC TELESCOPE ABERRATIONS     
4.1. Spherical  Primary 2 Higher-order•  
4.2. Coma  
4.3. Astigmatism  
4.4. Defocus   
4.5. Fabrication errors 4.5.1. Optical tests
Double pass test Interferometry 
Foucault
Ronchi Waineo Hindle Dall/Ross Offner
4.6. Distortion 
4.7.
Field curvature
4.8. Chromatism axial• lateral effect
4.9. Optical coatings - effects

 5. INDUCED ABERRATIONS
5.1. Air-medium errors
Seeing error
Model limitations
Seeing and aperture
The seeing Strehl, resolution, OTF
5.2. Low-level turbulence, tube currents
5.3. Alignment errors
5.4. Forced surface errors

 6. EFFECTS OF WAVEFRONT ABERRATIONS
6.1. Aberrations and optical quality: Criteria
6.2.
General effects•  6.3. Object type related 2
6.4. Diffraction pattern  Star test
6.5. Strehl ratio  6.6. MTF• 2• 3•

 7.
OBSTRUCTION EFFECTS 2• 3 4 5

 8. REFLECTING OBJECTIVES
8.1. Newtonian off-axis collimation diagonal flat
8.2. All-reflecting two-mirror 2 3 4 5 6
8.3. Three-mirror
Cassegrain-Gregorian Paul-Baker FAA
8.4. Off-axis and tilted elements
Herschelian schiefspiegler/Stevick
• off-axis Newtonian

 9.
REFRACTING OBJECTIVE Achromat Apo 2
Designing

 

 10.
CATADIOPTRIC TELESCOPES
10.1. SUB-APERTURE LENS CATs 2 3 4
10.2.
FULL-APERTURE LENS CATs
10.2.1. Dialytes Hamilton Schupmann Busack/Honders
10.2.2. Schmidt corrector
Schmidt camera 2
Wright, Baker SN SCT 2 3 SC camera
10.2.3. Meniscus corrector
Bowers/Maksutov camera 2 MN MCT
2 3•
10.2.4. Houghton corrector
Houghton camera
2 HN HCT 2 3 4 5

11. Special purpose telescopes Solar

 12.
TELESCOPE EYEPIECE 2 3

 13.
THE TELESCOPIC EYE
Aberrations
2 3 4 5 6 Response 2

 14.
TELESCOPES Past ATM Observatory Commercial
  
APPENDIX: Telescope specifications 2 3 4

• UPDATED Aug-Oct 2014
NOTE TO FIREFOX USERS: View>Zoom out can help display subscripts partly legible

 


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Web-published on July 14. 2006. by Vladimir Sacek

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