Appendices

Appendix A: Refractor Design Through the Centuries

1761–1764 Clairaut Doublet – Second & Third surfaces in contact (four possible bendings)

1898 Harting Doublets – aplanatic (coma-free) cemented lenses crown forward

Contact doublets – with air gap, crown forward:1760 Dollond1760–1810 Clairaut, d’Alembert, Boscovitch, Kleugel1815 Fraunhofer1829 Littrow1846 Clark modified Littrow1855 Cooke1864 Grubb1879 Hastings-Brashear

Contact doublets – with air gap, flint forward:1758 Dollond1842 Stenheil1879 Hastings

267

Appendices

Contact triplets – crown forward:1763 Dollond

Non-contact doublets – crown forward:1860 Clark1867 Gauss1945 Baker Aplanat1980 Buchroeder

Non-contact doublets – flint forward:1867 Gauss

Apochromatic doublets:1886 Czapski – modified Fraunhofer1888 Czapski – modified Gauss flint forward1892 Cooke-Taylor f/18 (Taylor)1899 Zeiss A halb (Konig) f/201926 Zeiss AS f/10 (Sonnefeld)1987 Gregory Fluor-Crown f/15

Apochromatic triplets:1894 Cooke-Taylor PV f/18 (Taylor)1896 Zeiss B f/15 (Konig)1950 Zeiss F f/11 Schwerflint (Kohler & Conradi)1977 Busch HAB f/15 (halbapochromat bausatz) oiled - not sealed1981 Christen f/10 – modified Taylor PV/Zeiss B oiled - Kapton sealed1986 Zeiss APQ f/10 fluorite1990 Fluor-crown FPL51 / FPL53 air spaced1995 Fluor-crown FPL53 oiled – Kapton sealed

Apochromatic quadruplets:1999 Laux FPL53 f/7

Dialytes:1828 Rogers1834 Plossl1840 Petzval1985 Christen (Fraunhofer doublet with triplet sub-aperture corrector)2000 Chromacorr (Fraunhofer doublet sub-aperture corrector)2006 Zerochromat (Single OG with dialytic field corrector)

268

Appendices

Appendix B: Double Star Tests for Refractors of Various Apertures

The Dawes limit for your telescope (in arc seconds) is given by 4.56/D where D is the aperture of your telescope in inches. Use a high-power eyepiece yielding 30–50× per inch of aperture on a calm night. Pairs displaying wide separations are chosen to test your telescope’s ability to pick out pairs that vary greatly in brightness.

Tests for a 2.4-in. (60 mm) ScopeStar Right ascension Declination Mag Separation

eBootis 14 h 45 min +27° 04 2.6, 4.8 2.9”″

aUrsa Minoris 02 h 32 min +89°16 2.1, 9.1 18.6”″

lOrionis 05 h 35 min +09° 56 3.5, 5.5 4.3”″

Tests for a 3-in. (76 mm) ScopeStar Right ascension Declination Mag Separation

dCygni 19 h 45 min +45° 08 2.6, 6.3 2.5”

iCassiopeiae 02 h 29 min +67° 24 4.6, 6.9 2.9”″

qAurigae 06 h 00 min +37° 13 2.7, 7.2 3.8”″

pLupi 15 h 05 min –47° 03 4.6, 4.6 1.6”″

Tests for a 4-in. (102 mm) ScopeStar Right ascension Declination Mag Separation

mCygni 21 h 44 min +28° 45¢ 4.7, 6.2 1.9”″

aPiscium 02 h 02 min +02° 46¢ 4.1, 5.2 1.9”″

gVirginis 12 h 42 min –01° 27¢ 3.5, 3.5 1.3”″

bMu. scae 12 h 46 min –68° 08¢ 3.5, 4.0 1.1”″

Tests for a 4.7-in. (120 mm) ScopeStar Right ascension Declination Mag Separation

32 Orionis 05 h 31 min +05° 57¢ 4.4, 5.8 1.2”″

k Leonis 09 h 25 min +26° 11¢ 4.5, 9.7 2.4”″

a Scorpii 16 h 21 min −26° 26¢ 1.0, 5.4 2.5”″

269

Appendices

Tests for a 6-in. (150 mm) Scope

Star Right ascension Declination Mag Separation

zBootis 14 h 41 min +13° 44¢ 4.5, 4.6 0.8”″

z Herculis 16 h 41 min +31° 36¢ 2.9, 5.5 0.8”

a-2-Capricorni 20 h 18 min −12° 33¢ 3.6, 10.4 6.6”″

lCentauri 11 h 36 min −63° 01¢ 3.1, 11.5 16”″

270

Appendices

Appendix C: Useful FormulaeEyepiece magnification = focal length of the objective/focal length of

eyepiece.

Field of view (angular degrees) = Apparent field of view of eyepiece/eyepiece magnification (approximate). A more accurate formula is given by: (eye-piece field stop diameter/focal length of telescope) × 57.3.

Focal ratio of telescope = Focal length of telescope/objective diameter.

Chromatic aberration (CA) index = Focal ratio of telescope/aperture (in inches).

Exit pupil = telescope aperture (mm)/magnification of eyepiece.

Depth of Focus = DF=±2DF2, where D is the wavelength of light and F is the focal ratio of the telescope.

Angular measurement = 1 angular degree = 60 min of arc (60¢) = 3,600 s of arc (3,600′′)

Limiting magnitude of a telescope = 6.5 − 5 log d + 5 log D, where d is the diameter of the observer’s pupil when dark adapted and D is the aperture of your telescope.

271

Appendices

Appendix D: GlossaryAbbe number: A number indicating the dispersion of an optical substance.

The larger the Abbe number (V), the lower its dispersion. Numerically,

1,D

F c

nV

n n−

=−

where nD, n

F and n

C are the refractive indices of the material at the wave-

lengths of the Fraunhofer D (yellow)-, F(blue)- and C(red)-spectral lines (589, 486 and 656 nm respectively).

Achromat: Type of refractor that uses a doublet objective made from crown and flint glass.

Airy disc: The disc into which the image of a star is spread by diffraction in a telescope. The size of the Airy disk limits the resolution of a telescope.

Alt-azimuth: A type of mount, like a simple photographic that allows you to make simple movements from left to right (azimuth) and up and down (altitude).

Antireflection coating: The application of a very thin layer of a substance (e.g. magnesium fluoride) to the surface of the lens which has the effect of increasing light transmission and reducing internal reflections in the glass.

Apochromat: Type of refractor that uses exotic glass types that produces colour-free images in focus.

Astigmatism: An aberration that occurs when there is a difference in the magnification of the optical system in the tangential plane and that in the sagittal plane.

Autoguider: An electronic device that makes use of a CCD camera to detect guiding errors and makes automatic corrections to the telescopes drive system.

Barlow lens: A concave achromatic lens with negative focal length, used to increase the magnification of a telescope.

Chromatic aberration: A phenomenon caused by the focusing of light of different wavelengths at different positions relative to the objective.

Chromatic Aberration (CA) Index: A measure of color correction in achro-mats found by dividing by the focal ratio of the telescope by its aperture in inches. The larger the CA index, the better color corrected the instrument.

272

Appendices

Coma: An aberration which causes a point object to be turned into a pear or comet-shaped geometry at the focal plane, and which most commonly manifests itself off-axis.

Depth of focus: A measure of how easy it is to attain and maintain a sharp focus. The larger the focal ratio of your scope, the greater its focus depth.

Diffraction: A wave phenomenon which occurs when waves bend or distort as they pass round an obstacle.

Dispersion: The tendency of refractive materials (e.g. a lens or prism) to bend light to differing degrees causing the colors of white light to separate into a rainbow of colours.

Doublet: A telescope with an objective made from two glass elements.

ED: Short for extra low dispersion, usually referring to glass which focuses red green and blue light more tightly than a regular crown flint objective resulting in better color correction.

Extrafocal: Outside focus.

Eye relief: the distance from the vertex of the eye lens to the location of the exit pupil.

Fluorite: A mineral with very low dispersion made from crystals of calcium fluoride (CaF

2).

Focal length: The linear distance between a lens and the point at which it brings parallel light rays to a focus.

Focal ratio: The focal length of a telescope divided by its aperture.

Fresnel rings: The set of diffraction seen round stars just outside and inside focus.

Intrafocal: Inside focus.

Magnification: The factor by which a telescope makes an object larger.

Minus violet filter: A filter designed to block shorter wavelengths of visible light (blue and violet) to reduce the spurious color seen round bright objects using achromatic refractors.

Multi-coated: The lenses are antireflection coated with more than one layer of coatings.

Petzval: A four element optical design consisting of two widely spaced dou-blets used to reduce chromatic aberration and flatten the field of view for photographic applications.

273

Appendices

Refraction: A wave phenomenon that causes light to change direction (and consequently the speed) upon entering or leaving a transparent material.

Refractive index (n): A measurement of much light slows down in the mate-rial it is travelling through. If a given glass has a value of n = 1.5 light slows down on entering the glass to 1/1.5 or 66% of the speed of light in air. Experimentally, n = sin i/sin r where i and r are the angles of incidence and refraction of the glass, respectively.

Refractor: Type of telescope that uses glass lenses to bring light to a sharp focus.

Spherical aberration: The inability to focus rays of light emanating from the centre and edges of a lens at a single point in the image plane.

Spherochromatism: The variation of spherical aberration with wavelength (colour) of light used.

Triplet: A telescope with an objective made from three separate glass elements.

274

References

History of the RefractorKing, H.C., The History of the Telescope, (1955), Dover.Hoskins, M. (ed.), The Cambridge Concise History of Astronomy, (1999), Cambridge Univer-

sity Press.Warner, D.J., Alvan Clark & Sons, Artists in Optics, (1968), Smithsonian Institution Press.

Refractor OpticsBell, L., The Telescope, (1981), Dover.Suiter, H.R., Star Testing Astronomical Telescopes, (2009), Willmann-Bell.Roth, G.D., The Amateur Astronomer & his Telescope, (1972), Faber & Faber.Kitchin, C.R., Telescopes and Techniques, (1995), Springer.Pfannenschmidt, E., Sky & Telescope, April 2004, pp 124–128.Binder, A., Sky & Telescope, April 1992, pp 444–450.Robinson, L.J., Outdoor Optics, (1990), Lyons and Burford.www.brayebrookobservatory.org The website of Christopher Lord, an authority on refractor

optics and double star observing.

275

References

Observational Astronomy BooksRidpath, I., & Tirion, W., Star & Planets, (2007), Collins.Ridpath, I.(ed.), Norton’s Star Atlas and reference Handbook, (2003), Longmann.R Consolmagno, G. & Davis, D.M., Turn left at Orion, (2000), Cambridge University Press.P Argyle, B.(ed.), Observing and measuring Double Stars, (2004), Springer.Haas, S., Double Stars for Small Telescopes, (2006), Sky Publishing.Mullaney, J. & Tirion, W., The Cambridge Double Star Atlas, (2009), Cambridge University

Press.Price, F.W., The Planets Observer’s Handbook, (2000), Cambridge University Press.

General Guides to EquipmentBackich, M., The Cambridge Encyclopedia of Amateur Astronomy, (2003), Cambridge Univer-

sity Press.Dickinson, T. & Dyer, A., The Backyard Astronomer’s Guide, (2008), Firefly Books.Harrington, P.S., Star Ware, (2007), Wiley.Mobberley, M., Astronomical Equipment for Amateurs (1998), Springer.

AstrophotographyRatledge, D., Digital Astrophotography; the State of the Art, (2005), Springer.Reeves, R., Introduction to Digital Astrophotography, (2005), Willmann-Bell.

Recommended Monthly Periodicals

Astronomy Now; the leading and best established British astronomy magazine.BBC Sky at Night Magazine: a popular choice amongst UK amateurs.Sky & Telescope and Astronomy magazines; for up to the minute reviews and all the latest

news, with a North American slant.Astronomy & Space; published by Astronomy Ireland, a good resource for all things astro-

nomical in the Emerald Isle.

276

References

Websites of Interest to Refractor Enthusiasts

Vladimir Sacek’s excellent website on telescope optics www.telescopeoptics.net.Roger Ceragioli’s Refractor Construction Page, http://bobmay.astronomy.netBack, T.M., Defining Apochromatism, http://geogdata.csun.edu/~voltaire/tmb/definition.

htmlwww.excelsis.com: A surprisingly good review site for telescopes and astronomical accessories.www.cloudynights.com: A superb resource to the astronomical community.www.Astromart.com: A market place for astronomical ware and equipment reviews.www.telescopejunkies.comwww.iceinspace.com.au: An excellent online resource for Australian amateurs.www.Scopereviews.com: Ed Ting’s eclectic website featuring mini-reviews on some nice

refractors of older pedigree.

277

AAbbe, E., 100–101, 103–104

criterion, 104number, 102

Aberration, 5, 23, 41, 57, 77, 86, 99, 118, 132, 143, 167, 190, 223, 248

Achromat, 15, 20–75, 77, 78, 81–84, 99, 100, 104–105, 109, 121, 124, 143, 168, 194–195, 223, 227, 228, 230, 234, 245, 249–254

Airy disc, 25, 26, 35–36, 47, 61, 69, 88, 99, 139, 151, 158, 226–228, 249–250, 260

Aitken, R.G., 262Alt-azimuth mount

AZ3, 210AZM, 214–215cube, 216, 217EZTouch, 213, 214field de-rotator, 217Minitower, 216, 217motorized, 45, 172, 202, 214–217, 258Porta, 210–211SLT, 216SynScan, 215–216Teegul, 211Voyager, 211

Antareselite achromats, 67, 68

Anti-reflection coatings, 20, 32, 67, 90, 147–148, 255

APMAPM/LZOS 105mm, 163

Apochromat (Apo), 20, 37, 52, 62, 78, 88, 99, 109, 129, 143, 167, 188, 224, 233, 245

ApogeeGalileo scope, 236

Astrophotography, 46, 49, 135, 136, 180, 217, 218, 243, 264

AstrophysicsGran turismo, 146starfire EDT series, 144–147Stowaway, 144Traveler EDFS, 144, 147

Astro-Professional115mm ED, 154

ASTRO-TECHAT66, 133AT72ED, 134AT106ED, 154AT111ED, 154

Astro telescopes, 53Autoguiding, 218, 240, 242

BBack, T.M., 82, 104, 162Baffles, 33–34, 49, 51, 170, 256Baker, J.G., 28Barlow lens, 42, 114, 190–192Bevis, J., 9Binning, 239Binoviewers, 148, 163–164, 203–204Blooms, 32, 239

Index

279

Index

Bosmabeta, 49, 584-inch F/10, 65

Brashear, J., 18, 23, 83Bresser

Messier R127L, 73Messier R152S, 53, 55, 56

Burgess TMB planet hunter, 59–61

CCA. See Chromatic aberrationCA index

conrady standard, 25, 259sidgwick standard, 25, 259

Campani, G., 6Carton, 89Cassini, G.D., 6, 261CCD

camera, 106, 107, 135, 165, 175, 176, 178, 180, 200, 202, 238–240, 243, 246

imaging, 135, 136, 165, 175, 180, 198, 202, 238–240, 242–243, 246

CelestronC–4R, 62, 63CR–150HD, 70, 74Omni 102, 62, 63Omni 120,

Cheshire eyepiece, 221, 222, 229, 255Christen, R., 144Chromatic aberration (CA), 5–6, 8, 10, 24–27, 36,

41, 42, 44, 46, 52, 54, 64, 75, 83, 86, 94, 99, 101, 107, 118, 132, 136, 148, 168, 177, 181, 223, 224, 227, 248

Clark, A., 15–17, 20, 22, 83, 92–95, 247, 255Collimation, 47, 73, 81, 89, 121, 201, 203, 221, 255,

265Coma, 27–29, 35, 44, 48, 61, 66, 91, 100, 103–104,

139, 158, 167, 173, 228–230, 250, 255, 259, 265Contrast enhanced diagonals (CED), 198Cooke, T., 13, 14, 100, 254, 255, 257

DDawes, W.R., 16, 231

limit, 187, 230–231Daylight tests, 41, 132, 222, 223, 225–226, 229, 230Defocus aberration, 29, 30, 252, 263, 265Denkmeier, 202Depth of focus (DF), 5, 7, 30, 68–69, 78, 106, 182,

200, 248, 252, 254, 262Descartes, R., 5D&G optical, 77Diagonal

60°, 12890°, 40, 123, 128, 196CED, 198dielectric, 43, 128, 148, 158, 197–198

Dialyte, 11Diffraction limited, 35, 36, 104–105Digiscoping, 233–238Distortion

barrel, 29, 229pincushion, 29, 229

Divini, E., 6Dollond, G., 190Dollond, J., 9, 10Dollond, P., 9Dorpat refractor, 12, 132, 218, 261Double stars, 7, 16, 26, 31, 41, 57, 58, 60, 64, 68,

72, 75, 78, 79, 89, 91, 92, 95, 118, 123, 139, 141, 153, 168, 186, 188–190, 198, 230–231, 249, 250, 252, 253, 258, 260–263, 265

Doublet, 9, 21, 40, 72, 77, 85, 101, 109–125, 143, 168, 191, 231, 240, 247

EED glass, 107, 109, 116, 119, 122, 144, 151, 154,

177, 245Equatorial Mount

Celestron GC–4 & GC–5, 62, 218Losmandy GM8 & GM11, 219Skysensor 2000, 218Sphynx, 218Vixen Great Polaris, 218

Exit pupil, 126, 187, 203, 204Explore scientific, 154, 188Eyepiece

ethos, 188, 257illuminated reticle, 242monocentric, 187, 189Nagler, 44, 49, 133, 136, 137, 167–169, 173,

188, 190orthoscopic, 52, 113, 148, 203Plossl, 41–42, 52, 62, 69, 72, 79, 110, 138, 170,

187, 191, 201, 260wideangle, 29, 58, 61, 65, 83, 131, 138, 159, 170,

187–189, 196, 229Eye relief, 4, 126–127, 188–192

FField of view

apparent, 6, 65, 187real, 28

FiltersHb, 195–196minus violet, 26, 49, 56, 72, 82, 194–195,

198, 230OIII, 195–196, 240UHC, 195–196Wratten, 26, 46, 53, 192–195

Flamsteed, J., 6Focal length, 5, 24, 40, 57, 77, 85, 100, 109, 125,

143, 168, 187, 216, 223, 239, 245

280

Index

Focal ratio, 24, 39, 61, 81, 91, 106, 118, 145, 180, 187, 223, 242, 248

FocusersFeathertouch, 117, 158, 162, 163, 164,

200–201Moonlight, 201rack and pinion, 40, 51, 58, 59, 68, 74, 136,

198–200, 202, 256Steeltrack, 202, 204, 257

Fraunhofer, J., 12–14, 16, 21, 27, 85, 218

GGalileo, 3–5, 235–236Glass

crown, 9–12, 20–23, 28, 100, 107, 124, 143, 151, 168, 174

flint, 9–12, 20–23, 28, 100, 107, 124, 143, 168, 174

fluorite, 101–103, 106, 116–119, 130, 136, 143–144, 153, 168, 173, 176–177

FPL–51, 102, 103, 119, 132, 134, 153, 154FPL–53, 102, 103, 119, 151, 153, 154, 156,

160, 162Ohara, 102, 103, 119, 153OK–4, 112SD, 55, 102–103, 111, 174

GPU102/640, 149127/890, 150127/1200, 149–150

Gregory, J., 8Grubb, H., 19Guinand, P.L., 12

HHall, A., 18Harriot, T., 4Helios

6-inch F/8, 72Hevelius, J., 5, 6, 261, 262Hooke, R., 7Hutech-Borg

Miniborg 45ED, 135125SD, 117

Huygens, C., 5–6

IiOptron

Versa 108ED, 122ISTAR Optical, 265

KKepler, J., 4

LLeica

Televid 82, 82, 129, 130, 131Lick refractor, 18, 262Lippershey, H., 3Littrow, J., 22Ludes, M., 79, 81, 162, 163LZOS, 162, 163

MMagnesium fluoride ((MgF

2), 20, 32, 90, 256

Magnification, 4, 24, 40, 58, 77, 88, 109, 126, 145, 168, 186, 211, 225, 235, 249

Maskelyne, N., 11Meade

AR5, 74–75AR6, 74Series 5000 127 ED, 152, 153Series 5000 80mm ED, 153

Minox DCM, 237, 238Moorehall, C., 8Multicoatings, 32, 33, 48, 51, 60, 62, 80, 85,

181, 189

NNeoachromat, 55, 107Newall, R.S., 15Newton, I., 8–10

OOrion telescopes USA

EON series, 1114.7-inch F/8 refractor, 69–72, 78, 106,

160, 181premium 110 ED, 122Shorttube 80, 40, 250Shorttube 90

PPentax

105 SDP, 177–179100 SDUF II, 179–180

Petzval, 53–55, 107, 131, 132, 167, 169, 172, 176, 177, 180

Pfannenschmidt, E., 223, 224Pixels, 234, 238–240Powermate, 44, 170, 177Poyser, I.R., 69, 70, 254Prism

diagonals, 58, 123, 124, 127, 128, 133, 148, 196, 235, 256

Porro, 127roof, 127

281

Index

RRayleigh limit, 35, 147, 203Rich field telescope, 36, 43, 45, 46, 49, 53,

79, 80, 92, 118, 133Roger, A., 11Romer, O., 6

SSacek, V., 66Scheiner, C., 4Seidel aberrations, 27, 29, 68, 167, 182, 228–229,

250, 251, 254, 263, 265Skylight telescopes

F/15 achromat, 147, 195, 251–252Skywatcher

BK1021, 63BK15012, 7180ED, 109–113, 246100ED, 111–114, 116, 139, 169120ED, 114, 115, 117Equinox series, 111Light Chariot, 44–45, 50StarTravel Shortubes, 43, 45

Smakula, A., 20Special dispersion (SD), 55, 102–103, 111, 174Spherical aberration, 7, 10–12, 27, 28, 30, 35, 36,

43, 44, 47, 49, 52, 61, 62, 75, 78, 83, 91, 102, 104, 105, 123, 124, 133, 139, 143, 151, 158, 167, 224–226, 228–231, 251, 255, 259, 265

Spherochromatism, 28, 100, 159, 167, 228Spotting scopes, 10, 235, 246Star test, 24, 42, 44, 45, 47, 52, 54, 61, 69, 87,

89, 99, 111, 121, 133, 139, 151, 153, 164, 226–228, 231, 251, 259

Steinheil, C.A., 23StellarVue

80/9D, 58–60, 121Nighthawk (AT1010), 46–49, 59, 121SV102 ED, 121SVR 130, 160–162SV80S, 160–161SV90T, 162

Strehl, K., 36peak Strehl, 36, 104polychromatic Strehl, 116, 251

Suiter, H., 99, 104, 227, 231Swift, 87–89Synta, 66, 74, 78, 79, 109, 210, 246

TTakahashi

FS 102, 116–118, 151FS128, 117, 118FS60C, 136–138Sky 90, 118–120, 173, 174TOA 130, 118, 149–151

TOA 150, 151TSA102, 151, 178

Tal100R, 66, 67, 73, 168, 224, 225127R, 72, 73100RS, 66

Tasco, 86–89Taylor, H.D., 20, 100, 104, 263Telescope Engineering Company (TEC), 146–148,

156, 203, 248Teleskop-Service (TS)

TS 102, 52, 53TeleVue (TV)

genesis, 67, 167–169Nagler zoom, 136, 173, 190NP 101, 118, 169, 174, 175NP127, 175, 176NP101is, 174, 175NP127is, 175Sky Tour, 169, 172, 212TV 60, 128, 137, 138TV 76, 138–140TV85, 112, 174TV101, 169–174TV 102, 110, 139TV 60is, 137TV 102is, 139

Telextender, 191Towa, 89, 90, 219–220Triplet, 11, 100, 102–104, 106, 107, 116, 117,

122–125, 131, 132, 141, 143–165, 167, 176, 179, 181, 191, 223, 227, 228, 231, 239, 240, 246, 248

UUnitron, 89–92, 259

VVignetting, 163, 174, 234, 238Vixen

A80MF, 58A80SS, 42, 43, 250AX103S, 181EDSF, 111102M, 61–62Neoachromat (NA)140, 55, 107

WWall, J., 200Wavelength, 5, 28, 30, 35, 36, 101,

102, 104, 105, 148, 195, 198, 225, 249, 251, 252

William opticsFLT 98, 156FLT 110, 147, 156, 157, 239

282

Index

FLT132, 157, 158, 159, 161–162FLT152, 53, 54, 121Megrez 72, 134Megrez 90, 50Megrez 110, 113, 122Megrez 88FD, 119, 120Megrez 80 triplet, 156Zenithstar 80, 48, 49Zenithstar 66 SD, 128, 132, 133, 134

YYerkes refractor, 18, 26

ZZeiss

APQ, 143Carl, 20, 100–101, 143Telementor, 87–89

283