Star Ware: The Amateur Astronomer's Guide to Choosing, Buying ...

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3 So You Want to Buy a Telescope! So you want to buy a telescope? That’s wonderful! A telescope will let you visit places that most people are not even aware exist. With it, you can soar over the stark surface of the Moon, travel to the other worlds in our solar system, and plunge into the dark void of deep space to survey clusters of jewel-like stars, huge interstellar clouds, and remote galaxies. You will witness firsthand exciting celestial objects that were unknown to astronomers only a generation ago. You can become a citizen of the universe without ever leaving your backyard. Just as a pilot needs the right aircraft to fly from one point to another, so, too, must an amateur astronomer have the right instrument to journey into the cosmos. As we have seen already, many different types of telescopes have been devised in the past four centuries. Some remain popular today, while others are of interest from a historical viewpoint only. Which telescope is right for you? Had I written this book back in the 1950s or 1960s, there would have been one answer: a 6-inch f / 8 Newtonian reflector. Just about every amateur either owned one or knew someone who did. Though many different companies made this type of instrument, the most popular one around was the RV-6 Dynascope by Criterion Manufacturing Company of Hartford, Connecticut, which for years retailed for $194.95. The RV-6 was to telescopes what the Volkswagen Beetle was to cars—a triumph of simplicity and durability at a great price! Times have changed, the world has grown more complicated, and the hobby of amateur astronomy has become more complex. The venerable RV-6 is no longer manufactured, although some can still be found in classified advertisements. Today, looking through astronomical product literature, we find sophisticated Schmidt-Cassegrains, mammoth Newtonian reflectors, and state-of-the-art refractors. With such a variety from which to choose, it is hard to know where to begin. 23
24 Star Ware Optical Quality Before examining specific types of telescopes, a few terms used to rate the caliber of telescope lenses and mirrors must be defined and discussed. In the everyday world, when we want to express the accuracy of something, we usually write it in fractions of an inch, centimeter, or millimeter. For instance, when building a house, a carpenter might call for a piece of wood that is, say, 4 feet long plus or minus 1/ 8 inch. In other words, as long as the piece of wood is within an eighth of an inch of 4 feet, it is close enough to be used. In the optical world, however, close is not always close enough. Since the curves of a lens or mirror must be made to such tight tolerances, it is not practical to refer to optical quality in everyday units of measurement. Instead, optical quality is usually expressed in fractions of the wavelength of light. Since each color in the spectrum has a different wavelength, opticians use the color that the human eye is most sensitive to: yellow-green. Yellow-green, in the middle of the visible spectrum, has a wavelength of 550 nanometers (that’s 0.00055 millimeter, or 0.00002 inch). For a lens or a mirror to be accurate to, say, 1/ 8 (0.125 mm) wave (a value frequently quoted by telescope manufacturers), its surface shape cannot deviate from perfection by more than 0.000069 mm, or 0.000003 inch! This means that none of the little irregularities (commonly called hills and valleys) on the optical surface exceed a height or depth of 1/ 8 of the wavelength of yellowgreen light. As you can see, the smaller the fraction, the better the optics. Given the same aperture and conditions, telescope A with a 1/ 8-wave prime optic (lens or mirror) should outperform telescope B with a 1/ 4-wave lens or mirror, while both should be exceeded by telescope C with a 1/ 20-wave prime optic. Stop right there. Companies are quick to boast about the quality of their primary mirrors and objective lenses, but in reality, we should be concerned with the final wavefront reaching the observer’s eye, which is double the wave error of the prime optic alone. For instance, a reflecting telescope with a 1/ 8wave mirror has a final wavefront of 1/ 4 wave. This value is known as Rayleigh’s Criterion and is usually considered the lowest quality level that will produce acceptable images. Clearly, an instrument with a 1/ 8 to 1/ 10 final wavefront is very good. However, even these figures must be taken loosely since there is no industrywide method of testing. Due to increasing consumer dissatisfaction with the quality of commercial telescopes, both Sky & Telescope and Astronomy magazines often test equipment and subsequently publish the results. Talk about a shot heard around the world! Both organizations quickly found out that the claims made by some manufacturers (particularly a few producers of Newtonian reflectors and Schmidt-Cassegrains) were a bit, shall I say, inflated. In light of this shake-up, many companies have dropped claims of their optics’ wavefront, referring to them instead as diffraction limited, meaning that the optics are so good that performance is limited only by the wave properties of light itself and not by any flaws in optical accuracy. In general, to be diffraction limited, an instrument’s final wavefront must be at least 1/ 4 wave, the Rayleigh Criterion. Once again, however, this can prove to be a subjective claim.
Page 2 and 3: STAR WARE The Amateur Astronomer’
Page 4: Contents Preface to the Third Editi
Page 7 and 8: vi Preface to the Third Edition Not
Page 9 and 10: viii Acknowledgments You, dear read
Page 11 and 12: 2 Star Ware Figure 1.1 The basic pr
Page 13 and 14: 4 Star Ware they are! It’s true t
Page 15 and 16: 6 Star Ware Figure 1.2 The Airy dis
Page 17 and 18: 8 Star Ware Table 1.3 Dawes’ Limi
Page 19 and 20: 10 Star Ware Figure 2.1 Artist’s
Page 21 and 22: 12 Star Ware Figure 2.3 Spherical a
Page 23 and 24: 14 Star Ware Figure 2.4 continued A
Page 25 and 26: 16 Star Ware an upright image, but
Page 27 and 28: 18 Star Ware Sir William Herschel,
Page 29 and 30: 20 Star Ware Cassegrains are design
Page 34 and 35: So You Want to Buy a Telescope! 25
Page 60: So You Want to Buy a Telescope! 51
Page 63 and 64: 54 Star Ware higher-power glasses a
Page 65 and 66: 56 Star Ware there are still severa
Page 67 and 68: 58 Star Ware for in a camera tripod
Page 69 and 70: 60 Star Ware Those views are incred
Page 71 and 72: 62 Star Ware (known earlier as Edmu
Page 73 and 74: 64 Star Ware evident around brighte
Page 75 and 76: 66 Star Ware however, at the amount
Page 77 and 78: 68 Star Ware Polaris FMT binoculars
Page 79 and 80: 70 Star Ware Figure 4.4 Orion’s V
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72 Star Ware Finally, Parks offers
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74 Star Ware may find too heavy to
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76 Star Ware more thoroughly, but i
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78 Star Ware Fujinon, the patented
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80 Star Ware finderscopes and a ple
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82 Star Ware Refractors are further
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84 Star Ware are sharp and contrast
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86 Star Ware tripod. Slow-motion co
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88 Star Ware for instance, is the e
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90 Star Ware angles to one another
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92 Star Ware Meade has also recentl
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94 Star Ware they are almost always
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96 Star Ware 102’s performance ca
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98 Star Ware eyepieces at any one t
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100 Star Ware and free of spurious
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102 Star Ware may select from their
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104 Star Ware but double-check on y
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106 Star Ware I set earlier, the Ra
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108 Star Ware absolutely textbook p
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110 Star Ware As we will see below,
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112 Star Ware eyepiece that comes w
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114 Star Ware therefore, their vers
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116 Star Ware The only optical prob
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118 Star Ware German equatorial mou
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120 Star Ware Figure 5.3 The NGT-12
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122 Star Ware As the name implies,
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124 Star Ware Meade also offers two
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126 Star Ware beefier version. All
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128 Star Ware eyepiece of the 20-in
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130 Star Ware All four XT telescope
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132 Star Ware In my opinion, if you
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134 Star Ware rings (an important c
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136 Star Ware Figure 5.5 The 4.25-i
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138 Star Ware can be built around e
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140 Star Ware problem on damp night
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142 Star Ware axis. Takahashi descr
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144 Star Ware The Classical design
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146 Star Ware Takahashi also offers
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148 Star Ware In practice, the view
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150 Star Ware you upgrade to that 8
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152 Star Ware 40,000 objects (50,00
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154 Star Ware any means. The 26-mm
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156 Star Ware 6 � 30 straight-thr
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158 Star Ware reflector of similar
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160 Star Ware off-axis, as with mos
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162 Star Ware employee. I thought t
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164 Star Ware Meade Instruments. Th
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166 Star Ware Perhaps the Mak’s b
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168 Star Ware manufacturer states t
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Table 5.2 Telescope Mounts 170 Manu
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Table 5.2 (continued) 172 Manufactu
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174 Star Ware indicates German equa
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176 Star Ware on “street” price
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178 Star Ware had been received and
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180 Star Ware Table 5.3 Some of the
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182 Star Ware Figure 6.1 A selectio
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184 Star Ware Table 6.1 Telescope A
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186 Star Ware (a) Narrow Field of V
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188 Star Ware of the brighter objec
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190 Star Ware Kellner. It took over
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192 Star Ware the 55-mm requires a
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194 Star Ware The consensus from al
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196 Star Ware quite sharp with exce
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198 Star Ware very tall. The 10-mm,
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200 Star Ware Cheapest of the cheap
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202 Star Ware 8 mm, enabling it to
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204 Star Ware Table 6.3 Barlow Lens
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206 Star Ware Okay, are they worth
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208 Star Ware Figure 6.5 Celestron
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7 The Right Stuff Congratulations o
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The Right Stuff 213 Some telescopes
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The Right Stuff 215 Table 7.1 (cont
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The Right Stuff 217 Table 7.2 Unity
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The Right Stuff 219 Figure 7.3 Tran
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The Right Stuff 221 either a narrow
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The Right Stuff 223 Table 7.4 (cont
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The Right Stuff 225 of the Sun (foc
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The Right Stuff 227 Table 7.6 Solar
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sunspot intricacies, and erupting p
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The Right Stuff 231 Tectron, AstroS
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The Right Stuff 233 view from the s
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The Right Stuff 235 Rubber Eyecups
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The Right Stuff 237 just like regul
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The Right Stuff 239 Amateur Astrono
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The Right Stuff 241 Introductory Bo
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The Right Stuff 243 Miscellaneous R
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The Right Stuff 245 Digital Setting
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The Right Stuff 247 Celestron’s A
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The Right Stuff 249 Table 7.12 Sugg
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The Right Stuff 251 Table 7.13 Film
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The Right Stuff 253 Figure 7.8 Came
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of imaging you are interested in do
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The Right Stuff 257 dynamic range i
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The Right Stuff 259 that the ST-10E
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The Right Stuff 261 to be desired,
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The Right Stuff 263 Flip Mirrors On
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The Right Stuff 265 No doubt about
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The Right Stuff 267 Table 7.15 Astr
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The Right Stuff 269 Figure 7.11 Tut
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The Right Stuff 271 Table 7.16 Anti
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The Right Stuff 273 Kendrick Astro
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The Right Stuff 275 The Sky / mount
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The Right Stuff 277 Although the mo
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The Right Stuff 279 Pro Domes come
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Figure 7.14 The Kendrick Astro Inst
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8 The Homemade Astronomer Amateur a
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Table 8.1 QuickCam Astro-Imager Par
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The Homemade Astronomer 287 image o
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Figure 8.5 Plans for the Kratz char
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The Homemade Astronomer 291 sily ma
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The Homemade Astronomer 293 drawing
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The Homemade Astronomer 295 Figure
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The Homemade Astronomer 297 a 0.25-
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The Homemade Astronomer 299 Once yo
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The Homemade Astronomer 301 Figure
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The Homemade Astronomer 303 as well
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Table 8.7 Planet Blocker Parts List
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The Homemade Astronomer 307 Table 8
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The Homemade Astronomer 309 Dremel
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Table 8.9 Crombie Observing Chair P
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The Homemade Astronomer 313 back in
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Figure 8.22 Plans for the Trott min
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Figure 8.23 P.J. Anway’s Lookum O
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Table 8.11 Lookum Observatory Parts
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9 Till Death Do You Part If this we
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Till Death Do You Part 323 Having a
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Till Death Do You Part 325 Consult
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Till Death Do You Part 327 Some clo
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Till Death Do You Part 329 on a lar
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Till Death Do You Part 331 houette
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Till Death Do You Part 333 To learn
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Till Death Do You Part 335 substant
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Till Death Do You Part 337 in size
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Till Death Do You Part 339 carton.
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10 A Few Tricks of the Trade A tele
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A Few Tricks of the Trade 343 To he
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A Few Tricks of the Trade 345 well
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A Few Tricks of the Trade 347 Figur
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Table 10.1 (continued) Oregon Star
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A Few Tricks of the Trade 351 the s
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Tri M33 A Few Tricks of the Trade 3
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A Few Tricks of the Trade 355 Polar
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A Few Tricks of the Trade 357 even
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A Few Tricks of the Trade 359 on th
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A Few Tricks of the Trade 361 Altho
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A Few Tricks of the Trade 363 on. I
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A. Binoculars Appendix A Specs at a
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Appendix A 367 Aper- Field of Exit
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Appendix A 369 Aper- Field of Exit
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Appendix A 371 Total Focal Tube Wei
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Appendix B Eyepiece Marketplace Foc
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Appendix B 385 Focal Apparent Compa
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Appendix C The Astronomical Yellow
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Campmor 810 Route 17 North, Paramus
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Web site: http://www.dewshields.com
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Product(s): Binoculars, reflectors,
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Web site: http://www.starlight-xpre
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United States Arizona Astronomy Sho
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New Hampshire Rivers Camera Shop 45
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Canada Alberta The Science Shop 316
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Phone: 61-02-9211-1606 316 St. Paul
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Appendix D An Astronomer’s Surviv
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412 Star Ware Telescopes and Equipm
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414 Star Ware Include the To Join,
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Star Ware Reader Survey To help pre
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Any particular likes or dislikes? (
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422 Index D&G Optical refractors, 8
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424 Index reflecting telescopes. Se
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