Brunson 771 - Cross-axis Collimation

49 Operation and Adjustment Manual
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Thistestshouldonlybeconductedifyouintendto
turnarightangleusingthecross‐axistelescope.If
youdointendtodothis,chancesareverygoodthat
youhaveasecondinstrumentatyourdisposal—and
thisinstrumentwillbeusedasareferenceinstrument
toconductthetest.We’llcallthetransitthatyou
wishtoadjustthe“testtransit”,andwe’llcallthesec‐
ondinstrumentthe“referenceinstrument”.
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1.Whensettingupthetesttransit,weneedtoob‐
serveonesimplerule.Wewantthecross‐axistele‐
scopesituateddirectly
overonepairofleveling
screws(Figure4.6).Roughlevelthisinstrument,and
illuminatethecross‐axistelescope.Besurethatthe
maintelescope’sfocusknobisturnedallthewayin
thedirectionoppositefrominfinity(toextremenearfocus).Thiswill
ensurethatthefocusslideisout
ofthewaysothatlightisvisible
throughthecross‐axis.Youcanverifythisbyeye,simplybylook‐
ingintothecross‐axisobjectivelenswiththelightturnedon.The
verticaltangentclampshouldbeleftlooseforthisentiretest.
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2.Setupthereferencein‐
strumentnearby,andbringit
tothesameheightasthe
first.(Youcanusealeveloran
alignmenttelescopeastherefer‐
enceinstrumentjustaswell.
Thesamegeneralstepsapply.)
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3.Makesurethereference
instrumentissetatinfinity
focusbyusinga
mirrororby
findingthereticleinthetest
transit’scross‐axistelescope.
Thencollimatethesetwo
telescopes,usingtheproce‐
duredescribedinChapter3
ofthismanual.Makeadjust‐
mentstothepositionofthe
referenceinstrumentuntilits
reticleisfairlyclosely
alignedwiththereticleinthe
testtransit’scross‐axistele‐
scope.
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4.Nowturnoffthelighting
inthetesttransit’scross‐axis
telescopeandturnonthe
Cross‐axisTelescope
Collimation
Description:Determineifthelineof
sightofthecross‐axistelescopeis
paralleltothehorizontalaxis.
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Tolerance:±1arcsecond.
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Affectedparameters:None.
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Requiredequipment:
Asecond76RHtransitorotherin‐
strument,lightingattachment,two
instrumentstands.
Generallyitishandyto
findinfinityfocusbyhold‐
ingamirroruptotheob‐
jectivelensofanillumi‐
natedtelescope.Whilethis
isconvenient,itisn’tman‐
datory.Itispossibleto
findinfinitybyturningthe
focusknoballthewayto‐
wardinfinityfocus,then
slowly“comingback”
whilewatchingforthereti‐
cleto
appearintherefer‐
enceinstrument.
Figure4.6