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Making Your Own Telescope - by Allyn J.Thompson



telescopetelescope mirror grinding


I discovered this book by talking with all the telescope makers and astronomy hobbyists that came here to buy plate glass. The few who had a copy of this book told me what a prize it was. The level of detail in this book is incredible. You rarely see that today.


So...

I've got a digital copy  for sale.

$7

If you would like a copy email me at:



You'll have to type that in.

It's a picture so the spammers can't get it





rough grinding pitch lapearly reflecting telescopetripod









angular magnification filament testangular magnification

CONTENTS

Note: If you're looking for something specific most web browsers have a "find" tool listed under "edit".
That should help.

Chapter I. STORY OF THE TELESCOPE
................................................................

1 The Galilean Telescope...
2 The Keplerian Telescope...
3The Gregorian Telescope ...
6 The Cassegrainian Telescope ...
7 The Newtonian Telescope ...
8 Further Developments ...
11 Herschel's Contributions ...
14 The Achromatic Refractor...
16 The Modern Era...
18 Reflector or Refractor? ...
21 What Size Reflector?... 24

Chapter II. MATERIALS AND EQUIPMENT
........................................
27 The Template ...
29 Channeling Tool...
30 Grinding Stand...
30 Mirror Testing Rack ...
30 Testing Stands...
31 FoucaultTesting Device...
32Theory of the Foucault Test...

Chapter III. MIRROR GRINDING.
.................................
39 Strokes ...
39 What Abrasive Does ...
40 How the Curve Is Obtained ...
41 We Go to Work...
42 How to Determine Contact...
45 Cleaning Up ...
47 Fine Grinding ...
47 Examining for Pits ...
 
Chapter IV. THE PITCH LAP
............................

Making the Lap ... 51
A Better Lap ... 53
MakingContact....... 57

Chapter V. POLISHING - TESTING - CORRECTING
...................................................

Theory of Polishing ... 59
Polishing Procedure ...
60 How to Use the Foucault Device ...
62 Further Polishing...
67 Examining for Pits...
68 Correcting...
69 Turned-down Edge ...
70 Turned-up Edge ...
70 Correcting the Oblate Spheroid...
71 Correcting the
Hyperboloid... 72

Chapter VI. THE PARABOLOID
............................
The Reference Spheres... 75
Knife-edge Magnification ...76
Surface Tolerance ... 77
Error of Observation ... 78
Testing the Paraboloid ... 78
Testing at Focus ...
85 Test forAstigmatism... 85
Parabolizing Strokes... 86
Aluminizing ... 89

Chapter VII. THE DIAGONAL
.............................
 
How Large a Diagonal? ... 91
Preliminary Preparations...97
How Flat a Diagonal? ... 98
The Light Source... 99
Testing for Flatness... 100
Making the Diagonal... 103
The Lap ... 106
Polishing and Testing... 106
An Elliptical Flat... 108
 
Chapter VIII. TUBE PARTS-ALIGNMENT-THE FINDER
...............................................

The Mirror Cell... Ill
The Tube... 113
Eyepiece Support...114
Diagonal Holder...
116 Spider Support... 117
The Saddle...119
Optical Alignment... 120
The Finder... 121
 
Chapter IX. EYEPIECES AND RELATED PROBLEMS
.............................................

Magnification ... 124
Field of View... 126
Exit Pupil and Eye Relief...
126 Eyepieces... 129
Aberrations of the Eyepiece... 132
Assembling Eyepiece Components... 134

Chapter X. THE MOUNTING
.....................................
 
The Babbitted Bearings... 142
Further Suggestions... 145
A Portable Mounting... 145
The Tripod ... 146
Machining the Parts... 148
 
Chapter XL ALUMINIZING AND CLEANING
........................................

Aluminizing... 155
Packing for Shipment... 157
Care of the Optical Parts... 158

Chapter XII. SETTING CIRCLES - EQUATORIAL ADJUSTMENT
.......................................................

Making the Circles... 160
Adjustment of the Tube ... 161
Adjustment of the Polar Axis... 162
Sidereal Time from the Stars... 167
Locating True North by the Sun ... 167

Chapter XIII. OPTICAL PRINCIPLES - ATMOSPHERE - MAGNITUDES
.............................................................
The Diffraction Image of a Star... 171
Resolving Power ...172
Diffraction from Obstructions ... 175
Extra-focal Diffraction Rings ... 176
Atmosphere, and Thermal Disturbances... 177
The Limiting Visual Magnitude of a Telescope... 181
Aberrations of the Paraboloid... 182



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Galileos TelescopePipe Fittings for Telescope Mount Telescope Pipe Mount

Index

INDEX Aberration, chromatic, 4, 5; in eye, 173; of eyepieces, 132; paraboloid, 182; spherical, 4, 5, 10, 17; to find in mirror, 194 Abrasives, 27, 37; action of, 40; charges used, 48; how applied, 40, 49; series, 36 Absorption of light, lenses, 22; mir- rors, 15, 21; prism, 91 Achromatic lens, cost of, 19, 24; in- vention of refractor, 16 Adapter tube for eyepiece, 114 Adjustment, optical parts, 120, 189; polar axis, 162; telescope tube, 161 Airy disk, 171 Alignment of mirrors, 120, 189; star test for, 176, 190 Altazimuth mounting, 137 Aluminizing, 155; packing for ship- ment, 157; when to have done, 89 Aluminum film, care of, 158; most efficient, 20; quality of, 155; reflec- tivity of, 20, 21, 91, 155 American Ephemeris and Nautical Almanac, 162 Angular diameter, Jupiter, 4; moon, 96; stars, 171 Angular field of view, 92, 126, 130, 187 Anti-reflection coating, see fluoride coating Apparent field, 97, 126; of compound eyepieces, 130; of simple eyepiece, 129 Astigmatism, 183; in diagonal, 99; in mirror, 90, 184; test for, 85, 176 Atmosphere, 177, 181; correction for refraction in, 167 Babbitt metal, bearings, 142, 191; melting point, 143 Barnesite, 27, 28, 106 Beam-splitter, 100 Beeswax for lap coating, 53 Beveling, mirror, 45; tool, 42; un- equal disks, 195 Bibliography, 205 Blind flanges, 196 Carborundum, 27, 37; how applied, 40, 49; series, 36 Cassegrainian telescope, 7; perfora- tion loss, 95 Cell, for mirror, 111; springs for, 196 Center of mirror not used, 94 Cerium oxide, 27, 28, 106 Channeling tool, 30; using, 52 Chromatic aberration, 4, 132; defined, 5; in eye, 173 Circle of least confusion, 184 Circles, setting, 160 Cleaning, optical parts, 158; cleaning up during grinding, 47 Coefficient of expansion, fused quartz, 20; glass, 19; pyrex, 20; specu- lum, 19 Cold-pressing, 67, 68, 70, 71; in flat making, 203; onion sacking used in, 70 Coma, 90, 183 Concrete base, 139; suggestions and mixture, 195 Contact, how to determine, 45; mak- ing, 44, 57, 86 Correcting, 69; hyperboloid, 41, 62, 72; oblate spheroid, 71; turned- down edge, 70, 88; turned-up edge, 70 Correction of mirror, 76; tolerance, 77, 193 Curvature of field, 133 Curve, how obtained, 41, 43 Dewing of mirrors, 158 Diagonal, diffraction from, 95, 175; elliptical, 108; flatness required, 98; flexure in, 176; formula for size, 94; holder, 116; how long to make, 197; lap for, 106; making, 97, 103, 108; obstruction effect, 94; offset of center, 117, 189; polishing and testing, 106; proportions, 92; reason for, 90; shadow, 128; shape of, 92; size, 91, 95, 186; supports for, 116, 187; testing for flatness, 100 Diffraction, from diagonal, 95, 175; from vanes, 17S; image of star, 171, 177; ring test for turned edge, 70; rings, extra-focal, 176 Disks, broken, 195; unequal in size, 195 Dispersion, 6 Distortion, 133 Ellipsoid, definition of, 6, 73; for secondary, 6; undercorrected mirror, 76 Elliptical flat, 108 Emery, 27, 36; application of, 49 Ephemeris, American, 162 Equatorial, adjustment, 160; mount- ing, 137 Erecting eyepiece, 18 Error of observation, 78 Exit pupil, 126, 187 Eye, acute vision of, 169; fovea, 169; lens, position for observing, 127; pupil size, 128, 169; relief, 126; resolving power, 173; structure of retina, 169; visual limit, 173 Eyeglasses, see spectacles Eyepiece, 129; aberrations, 132: adapter tube, 114; apparent field, 97, 129; assembling components, 134; dimensions of, 130; Galileo's, 3; Herschel's, 16; Huygens, 11, 130; Kellner, 132; Kepler's, 3; Ramsden, 17, 131; support for, 114; terrestrial, 18; to find focal length, 127, 129; useful focal lengths, 130 Field of view, 25, 92-97, 129, 183, 187; best for finder, 122; defined, 126; of early telescopes, 4; of Galilean telescope, 3; useful, 90; with various magnifications, 96 Figuring strokes, 70, 71, 72, 86, 188; on optical flat, 203 Finder, 121; field of view of, 122 Fine grinding, 47; test for, 49 Flanges, blind, 196 Flat, see optical flat Flatness of surfaces, diagonal, 98; optical flat, 85, 204; plate glass, 99; prism, 99 Flexure, of diagonal, 176; of lenses, 21; of mirror, 19, 112, 176; star test for, 176 Fluoride coating, 22, 91, 132; for mirrors, 89, 157, 200 Focal length, 126; eyepiece, 127, 129; Herschel's eyepieces, 16; lens, 134; longest practical, 185; mirror, 44, 48, 49; of beginner's New- tonian, 25; paraboloid, 74; shortens in polishing, 48 Focal plane, 92 Focal ratio, defined, 8; higher, 191, 193; lowest for Newtonian, 188, 191, 193; of reflectors, 23; of re- fractors, 23 Focal surface, 90, 184 Focus, testing at, 85 Foucault test, device for, 31; inven- tion, 18; magnification, 76; sensi- tivity, 77; errors of, 78; theory of, 34; use of, 62, 78, 192, 193 Fovea, 169; extra-foveal vision, 170 Galilean telescope, 2 Garnet powder, 27 Gregorian telescope, 6, 12, 14 Grinding, 39; action of, 40; fine, 47; large mirrors, 192; length of stroke defined, 39; of broken disks, 195; motions in, 39; optical flat, 202; pressure used in, 40, 48, 50; pro- cedure for diagonal, 104, 105, 108; for mirror, 42, 47; speed of stroke, 40; stand, 30; stroke defined, 42; to remove turned edge, 88 Hadley's telescope, 11 Herschel wedge, 198 Herschelian telescope, 14 Hot-pressing, 57, 86; onion sacking used in, 106; of optical flat, 204 Huygens eyepiece, 11, 130 Hyperboloid, 67; cause of, 41, 67; correcting, 41, 62, 72; definition of, 6, 73; for secondary, 7; overcor- rected, 76 Insulation for tube, 179 Interference bands, explained, 100; observing with beam-splitter, 100; in testing, 101, 107, 204 Kellner eyepiece, 132; recommended, 188 Keplerian telescope, 3 Knife-edge, 32, 35; distance from pinhole, 33, 63; magnification, 76; sensitivity, 77; test at focus, 85; testing, 62, 192; testing error, 78; tolerance, 78, 193 Lap, for polishing, care of, 68, 69; cloth, 7, felt, paper, 59; for di- agonal, 106; for optical flat, 203; hard, best for flats, 203, shallow mirrors, 186; making, channeled, 51, molded, 53: pitch best for pre- cision optics, 59; pressing for con- tact, 57, 67, 68, 70, 71, 72, 86, 106, 203; soft, for deep mirrors, 188 Light, source, 99; wave length of, 77 Light-gathering power, 5, 169, 182 Light losses, absorption, 22, 91; re- flection, 19, 20, 21, 91; of specu- lum, 15, 21; transmission of coat- ings, 156 Limit of visibility, 173 Limiting magnitude, 181 Linear field of view, 92, 95, 126, 130 Lining for tube, 179 Long-focus telescope, 186, 190; early, 4 Magnesium fluoride, see fluoride coat- ing _ Magnification, defined, 124; of eye- piece, 125; of Galileo's telescope, 2; of knife-edge, 76; of telescope, 126, 127, 174; practical limits, low- est, 128, 187, highest, 174; theoreti- cal limit, 129; used by Herschel, 16 Magnitude of stars, 181; visual limit, 1, 25; telescopic limit, 25, 181 Materials, for mirror making, 27, 36; for secondary, 98 Mirror, achromatic, 6, 23; anchored in cell, 112; best size for beginner, 25; blanks, 27, sizes of, 185, broken, 195; can be left spherical, 186, 191, 194; care of, 158; cell, 111; center not used, 94; correction, 76; edge beveling, 45, 195; focal length of, 44, 48, 49; how long to make, 196, to polish, 67; radius of curva- ture of, 44, 48; reflectivity, 13, 19, 20; sticks to tool, 44, 50; tempera- ture effects on, 180; testing, 62, 78; testing rack, 30; world's larg- est, 21 Modern era in telescope making, 18 Monochromatic light, for interference testing, 99; sources, 100 Moon, angular size, 96; image size, 97; filter used on, 198 Mounting, 137; adjustment, 161; altazimuth, 137; attaching to pier, 196; equatorial, 137; German type, 138; machining the parts, 148; of pipe fittings, 139, 190, 191; parts, see individual parts; portable, 145 Nautical Almanac, American, 162 Newtonian telescope, 8, 93; field of, 96 North, to find, 167 North America nebula visible, 187 Oblate spheroid, 65; correcting, 71; definition of, 6, 73 Ocular, see eyepiece Optical flat, making, 202; precision required, 85, 204; for testing pa- raboloid, 85 Optician's three motions, 39 Overcorrection, 76, 88; tolerance, 78 Parabolizing, difficulties of, 186; glass removed in, 11, 74; Herschel's method, 14; strokes, 86, 188; tol- erance in, 193 Paraboloid, 10, 73; aberration of, 182; accuracy required, 78, 89, 171; correction for, 75, 76, 81: defini- tion of, 6, 73; field of, 96, 183; how obtained, 11, 73; difference from sphere, 75, 193; testing, 78, 193, at focus, 85 Paraffin, melting point, 105 Pier, for telescope mounting, 139, 196 Pinhole, distance from knife-edge, 33; theoretical position for, 76; to make, 33; visibility tests, 173 Pipe fittings for mountings, 139-146, 191, 196; specifications of, 142 Pitch, 28; tempering, 51; to dissolve, 108 Pitch lap, see lap Pits, in grinding, 37, 40, 50; in pol- ishing, 68 Plane surfaces, accuracy required, 85, 98, 204; test for, 100, 107, 204 Plastic lenses, 198 Plate glass, flatness of, 99; for tele- scope mirrors, 19, 21 Polar axis adjustment, 162 Polaris, correction for refraction, 167; distance from celestial pole, 162; ideal for star testing, 85 Polishing, agents, 7, 10, 27, 36, 60; mixture, 57, 60, 69; periods, dura- tion of, 62, 71, 188, 203; procedure, 60; pressure used in, 61; speed of stroke, 61; stance, 61; stroke used, 60, 106, 203; theory of, 59; time re- quired for, 67 Pressing, cold, 67, 68, 70, 71; hot, 57, 86, 106; onion sacking used in, 70, 106; optical flat, 203, 204; over- night, 72; periods, duration of, 67, 68, 71; weight used in, 57, 67, 106 Pressure, in grinding, 40, 48, 50; optical flat, 202; polishing, 61 Prism, as star diagonal, 92; effect of refraction in, 91; for Newtonian secondary, 91; light absorption in, 91; surface accuracy, 99; used with Foucault test, 33 Prolate spheroid, definition of, 6 Pyrex, 20; size of mirror blanks, 185 Quadrant, 1 Quartz, fused, 20 Radius of curvature of mirror, 44, 48 Ramsden, disk, 127; eyepiece, 17, 131 Rayleigh limit, 77 Real field of view, 126; for finder, 122 Reference spheres, 75 Reflection losses, air-glass surface, 22; aluminum, 20, 91; fluoride coated lenses, prisms, 22; silver, 19; spec- ulum, 15, 21 Reflectivity of, aluminum, 20, 21, 91, 155; fluoride coated surfaces, 22; glass, 22, 46, 91; silver, 19; spec- ulum, 13, 15, 21; prism versus diagonal, 91 Reflector, achromatic, 6, 23; cost of, 14, 16, 24; first, 8; versus refractor, 21; what size to make, 24; world's largest, 21; see also telescope Refraction, in prism, 91; of atmos- phere, 167 Refractive index, fluoride, 22; glass, 91 Refractor, cost of, 17, 18; first, 2; world's largest, 21 Resolving power, of eye, 173; tele- scope, 129, 172 Retina, structure of, 169 Rich-field telescope, 187 Rosin, for polishing lap, 28, 51 Rouge, 27; mixture, 57 Saddle for telescope tube, 119 Sagitta of paraboloid, 30 Secondary mirror, see diagonal Seeing, see atmosphere Setting circles, 160 Short-focus telescope, 187 Sidereal time, finding, 166, 167 Silver on glass, invention, 18; reflec- tivity, 19 Solar telescope, 198 Spectacles, invention of, 2; remove for observing, 127 Speculum metal, alloy, 13; coefficient of ex ansion, 19; reflectivity, 13, p 15, 21 Sphere, converted into paraboloid, 74; difference from paraboloid, 76; needed before parabolizing, 69; not needed for deep mirrors, 188; ref- erence, 75; test for, 46, 64 Spherical aberration, corrected, 17; defined, 5; in eye, 173, eyepiece, 134, lens, 4, mirror, 10 Spherical mirror, test for, 46, 64; when satisfactory, 186, 191, 194 Spider support, 117, 187; diffraction from, 175 Springs, to cut, 196 Star diagonal, 92 Star, angular size of, 171; diffraction image of, 171, 177; double stars, to separate, 172; magnitudes vis- ible, 1, 25, 181; number visible, 1 Stroke, defined, 42; length of, 39; parabolizing, 86, 188; speed of, grinding, 40, polishing, 61 Sun, observing, 197; projecting image on screen, 198; telescope for ob- serving, 198; used to locate true north, 167 Surface tolerance, for diagonal, prism, 98; for mirror, 77, 171, 193; for optical flat, 204; when can be relaxed, 188 Telescope, best size for beginner, 25; other recommended sizes, 185; find- er, 121; functions of, 4, 125, 169; larger than 6-inch, 191; light-gath- ering power, 169, 182; long-focus, 186, 190; magnifying limits, 128, 174, 187; resolving power, 129, 172; rich-field, 187; short-focus, 187; star magnitude visible in, 181; uses of, 24; ventilation, 178; world's largest, 21 Temperature, constant needed, 39, 204; effects on mirror, 180, flat, 204 Template, 29, 43 Terrestrial eyepiece, 18 Terrestrial observing, 177 Test for, alignment, 176; astigma- tism, 85, 176; fine grinding, 49; flatness, 100, 107, 204; flexure, 176; focal length of eyepiece, 127, 129, of lens, 134, of mirror, 44, 48; paraboloid, 78, 85, large mirrors, 192; pits in grinding, 50, in polish- ing, 68; radius of curvature, 44, 49; spherical mirror, 46, 64 Testing, at focus, 85; device, 31; on star, 85, 176; rack, 30; tolerable error, 78 Thermal disturbances, 177 Tolerance, see surface tolerance Tool, beveling, 42, 195; broken, 195; convex, to begin on, 195; thick- ness, 27, 37, 50 Tripod, 146; head, 148; leg links, 200 Tube, adjustment, 161; composition of, 113; diameter, 94; insulation for, 179; length, 113; long, subject to vibration, 187; saddle, 119; ven- tilating, 178 Turned-down edge, 61, 67, 68, 88; correcting, 70; test for, 70 Turned-up edge, correcting, 70; test for, 70 Undercorrection, 76, 87; tolerance, 78 Vanes, 118; diffraction from, 175; position of, 119, 187 Ventilation for telescope, 178 Vision, angle of, 169; distance of most distinct, 124 Visual acuity, 2, 173 Wave length of light, 77 Weight used in pressing, 57, 67; for diagonal, 106; for optical flat, 203 Working time, 196 Zonal mask, 79; for large mirrors, 192 Zonal testing, 78-83; of large mir- rors, 192 Zone, defined, 10; marking for test, 84