Amateur Telescope Making Advanced, Book Two (A Sequel to Amateur Telescope Making, Book One)

651 Pages·1952·38.52 MB·English

by  Albert G. Ingalls

AMATEUR
TELESCOPE MAKING
ADVANCED
(BOOK TWO)
A SeqfLel t0 AMATETTTRE LESCO?YI~AEK IXG
(BOOK ONE)
A~BERGT. INGALLESd'i tor
Contributing Editor, Scientific American
A eollection of contributionv to cclnateur
preciaion opticv by numerouv authorities
SCIEN'I'IFIC AMERTCAN, INC.
1952
.U7 rigltts ).~sPI<I.P~
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al1 ld~~zti~11~(,1i1g1f~Iint~hg? ~ S c;~~~diii:~vian
Eiglitli l'rilitiiig 1952
PRIXTED IX THE ITNiTED STATPS OF AYERICA
RIXGSPOIIT PI<EóS Ih<'. KlNCrYPOItT, TENlhSSEE
CONTENTS
HAVJND TO DO WITH THE COSSTRITCTION OF
OPTICAL INSTRUDIEA-TS
PACE
Backwoods Philosophy-Everest ....................................... 3
3Iirror Making 'l'echnic -
Sub-diameter Tools ..................................... . . . . . . . . 49
Making and Using Metal 'Tools-Chrk ................................ 55
Metal Mirrurs aricl Flats .......................................... 62
Astigmatism-Warner ................................................ 70
Prisms, Flats, Mirrors-Ferson ........................................7 5
Sninll-scalr Prism Produetion
A Quantitative Optical Test for Telescope Mirrors-King ..............1 04
Perforining tlie Ronclii Teat Qui~iiiiluti\ely
The Hartmann Test-Caliler .....................................1.0 9
Flats-Selby ....................................................1.1.3.
Notes on thc Opticnl Testing of Asplieric Surfaces-Selby ..............1 32
IIow to Make Rouge-Selby .......................................1 39
Small 1,e ns Wriril<les-Porter ........................................ 121
h1aking Eycl>.eco Lenses
An Introduction to Srnall Lenses-Clarlr ................................24 7
31üiiil>- oii 11akiiig Byepieces
Oculars at Smnll Cost-Patterson ......................................1 87
The Refractor-Met;~l Pnrts nnd Mounting-Triylor ......................1 92
The Refracting Selescope-Principies of Operation and Construction-
Havilancl .............................................. . .212
1Iainly on tlie Objeetive Lens
Target Scopes-Kirlcliam ..............................................2 62
For thc Rifleman
Testing Convex Splierical Surfaces-King ................................2 69
Collimatioii and Adjustrrient ...................................... 272
How to M;il<e a Diagoiial for a xentoninn-Hindle .................. 282
Making Srtting Circlrs ............................................2.8 7
Tclescope 1)rives-1, ower ............................................3. 03
Drives for 1.a rger Telescopes ............ ... ...................... 319
Hand-Wound Spring Drivrs for Telescopes .............................. 321i
She Sprin.gfielc1 Mouriting-Porter ....................................3 33
The Springfield Mounting-Pattern Making-Porter .................... 339
With Principies of Yolding and Casting
..............
Molding and Castiiig Springfield Mountiiig Parts-Ferson .3.1.i
Moldirig and Casting a Fork-Mason ..............................i3 6l
Sidelights on Molding and Casting
v
vi CONTENTS
PlOE
Machining the Springfield 3lounting.Piirter ............................3 65
Motor Drives, Coiiiiterweighting. Pier-Cpringfirl(1 Moiiiitiiip-Porter ....3 71
'I'he Riiilding tif a 19-Inch lieflecting 'I'elescop<.-Yoiiiig ..................3 76
r1 7 he Schinidt Carnera-Introductory-l<usht>ll ............................3 9.3
Theory and Design of Aplanatic Heflectors Eiiiployirip ;i Correctirig 1.eiis-
Wriglit ........................................................... 401
Ineluding tlie S<.IiriiidtC ;!iiirr;i
Notes on the Construction of an F/1 Schrni<lt C.rinera-Lo\ver ............4 10
The Camera Obscura-Dall ....................... ......................4 17
Indoor Telescopic Visiun-Terrestriiil Crlesti;il
Converting a Seth 'I'hornas Clock into a Sidere;tl Clock-l<uriy.tn ..........S 25
A Precision Clock-Soutlier ...........................................4.% 7
1l;tl;iii~:I Synchrotiom~( 'io<.l<
Micrometers ..........................................................4.4 7
A Simple Chronograph-Hay .................. .0. -
The Eval)oratiori Process for Cmiting Astronomical Mirrors- Strong ..... -467
Having to Do with Silvcring ...........................................4.7 7
The Amateur's Ohservatory-Scanlon .................................4.8 .4
h Bilateral Slit hlechanism-H;rriieh and I5rattain ...................... 503
Sliorts ...............................................................5.0 6
Building a Birefringent Polarizing Monochromator for Solar Pruminences-
Paul ...............................................................5. 2 1
I'AllT 11
HAVING TO no WITH sonm OF THE MORE PRXCTICAL
ASIJE<'TS OF OBSERVING
Researches with Our Instriiments-Halb.ich ...........................5.6 0
Definite, Systernütized Uses for Teleacopes
The Dewing of Optical Siirfaces-Steav?nsori ..........................5 76
Limitations of Vision with u. Tclescol>e-Dall... .........................5 79
Atmosphere, Te1escol)c arid Obierver-Douglass .........................5 65
Heflrctors versus Refractors-Pickering ................................6 06
U'oodin Tubes for Reflectors ..........................................6 16
Dealinp witli Spider Diflraction-Couder ...............................6.2 0
She Itichest-Field Telescope-Walkden .................................6.2 3
Index ...............................................................6.4.8
HAVING TO DO WITH THE CONSTHUCTTON OF
OPTICAL INSTRUMENTS
By A. TI7. EI'LREST
Pittsfield, 1\Iüssacliu\etts
A I'II~:UE o r OI,ASS
He lahorrd late into tlie night,
At rarly iiiorii' liis task rehulned,
To f;~bhioii thus a <lih!i o£ glass
Intu 2% sui~tleC UITT.C, not drep,
But iiieasiired only by the slindes of light
P'roin ;t uirnple yinholp me<lr in foil,
1ti.i.ealiirg to his prnctihe(1 eye
Tnil~rrfegtions intiiiitesimitl:
1T11til at Inst his skill producrd
A riirvr so truo tlie mind o€ mnn
Could not discern the val-ei.ing o€ a breath.
"Ju-t a pieee of dass," 'tws said,
B~iti ri tliat simple rlisk
Thr hrnrrnly hopt
Of suiis aiid siars, ?ea, iinirersi3s.
Rrvenlrd tlieir ~loryi n the sky
For iiian to ponder-and tidore.
-C. A. Olson
Westwood. N. J.
The first requirement in fiaurinp n mirror is a rlear conception of how
it should :ippear on llie testing stand, sincc it is hy compnring wliot we see
with ~v11:it we ciuglit to ser tlint wc cleterniine \vliat to do. Tliis :ippe:ir:ince,
with tlie knife-edge in come intermediate positioii, 11:~s been snid to resemble
that of n doiigtinut-and tlie an:ilogy is a good one, since, like arnateiir's
mirrors, there are al1 kinds of douglinuts-roiigh ones, smootli ones, dougli-
nuts witli lioles antl dougliniits mithout 'em.
Well, whnt is thr shape of tlie true paraboloidal doi~glinut? Witli Porter
at the otlirr end of the continent, ahoul :ill we can do in tlie way of showirig
this threc-dimensional appr:irance in two-dimensional space, is to draw its
cross-section only, nnd !e;~rei t to the reader to visualiee the surface of revo-
lution this rrprcsriits. She calcu1;ition of ttiis cross-section is a simple
niatter. In f;ict, tlie cross-section of thr paraboloid, a.: it appears witli the
lrnife-edge in nny iiscful position, may he covererl in :i single eclii;ttion. Let's
figure ttie tiiing out under a lieading somewhat in keeping with thc method
c f calculation.
For reacons wliich will brcome cle,tr latcr on, the logical referrnce sur-
face for our calculatioris will be a spliere whose center of curvature is at
3
4 MIRROR MAKING
the point of ohservation, Le., where the knife edge cuts tl~ec one of light.
Further to siinplify niatters, tliis refererice iphere mciy he inadc tangent
to the paraboloid at iti center, as in thc iipper par1 of Figure 1, mnking this
point the origin of coordinates and therehy rliminating the constant of in-
tegration. In this example we have chosen n sphere whose center of curva-
ture C prime is just outside of C, tlie center of curvature of the paraboloid's
center zone. Starting at the center, such ü sphere would lie outside the
Al1 drawings by the author
FIGTRE1
paraboloid as far as some zone X, bepond which it would lie within. Viewed
froni its center of curvature, tliis reference sphere would appear flat, its
apparent cross-section would be a straight line, and the apparent cross-section
of the paraboloid would be a curve, somewhat as sliown in the lower part
of the same figure.
An expression for the deviation of the paraboloid frum this or any other
reference sphere will involve the following two propositions, which will he
stated with a degree of accuracy equivalcnt to that of r2/R without the tail
end of the forrriula. This will permit the use of simple terms which will
introduce no measurable error iñ the calculations for our telescope mirror;
although, of coiirse, the error would be intolerable in similar calculations
for a large searcliliglit reflector.
M I R R O R MAKING 6
Proposition. 1: For the condition shown in Figure 2, the deviation of parab-
oloid from sphere varies as the fourth power of its radius r, and inversely
as the cube of its radius of curvature R. In mathemi~ticalt erms we woul<l
x4
write, y = - k-
R3
The minus sign is inserted to indicate that the curve bends away from the
ohserver. E'or the slope at any poiiit, the first theorem in elementary caicu-
lus (about al1 we remcmher) tells lis,
Proposition 2: When observed from first one and then the other, of
two points aloiig tlie axis iiear the center of curvature, the slope of any
zone changes in proportion to the radius x of the zone, in proportion to tlie
distance L) between the two points of observation, and in inverse proportion
to R. For the slope in one position compared with that in the other we may
*
write, = KD-2
dx R
wlience, y = KD- (4)
2R
A useful example of this would be a spherical mirror examined first from
its centcr of curvature, whcn it would appear flat and its apparent cross-
section would be the straight line shown in Figure 3. If now the knife-edge
be moved a short distance D toward the obberver, the surface will appear
concave, y varying in proportion to $2 as shown.
We may now investigate what would happen to the curve shown in Figure
2 if the knife-edge is moved toward the ohsrrver. The slope of each zone
would change in accordance with the law given in the preceding paragrnph,
which means that certain sets of y values determined by Prop. 2 would be
added to those determined by Prop. 1. For example, Figure 4 shows the re-
sult of adtling the zictual !/ va1ut.i of Figure 3 to thosr of Figure 2. As a use-
ful prol>osition, liowrrir, tlie riirrc :i<lditioii of tlie riglit-li;in<i iiienii)crs of
equations (1) and (A), givirig
x2
y = KD- - kR234
2R (5)
woiild mean notliing until wr rspress T< iii tcrrn.; of k. To do this me tn;iy
consider tliat ?/ is to reticli its riliis iiii~xiiriiiiii ;rt tlic point \vlirrt* tlic rurve,
surh us tlie onr sliown iri Figiire 1, iit Iiottom, or tli' oric hlioxvri iir Figiire .1.,
bec~iniesf lat at the crest. l'liis will be xvhen tlie slol>cs re~~reheritc.tbly tlie
* I"rc,unr: 3
values of Propositions 1 and 2 cancr! each other, Le., where
dx
alrence, K = &k- x2
DR2
x2
For tliis point iri tlie curvr, D = R-
Subslitutirig this valur of D in equation (6),
-.
and substituting this value of in cquntion (S),