45 Operation and Adjustment Manual
thesecondscale.Makeanoteofthisreading.
4.Nowrotatethestandards180°abouttheverticalaxis(thistime,
don’trotatethetelescopearoundthehorizontalaxis).Usingthe
horizontaltangentadjustmentscrew,setbackonthepositionorigi‐
nallychoseninstep2.
5.Onceagain,plungethetelescope180°tosightatthesecond
scale.Takeasecondreadingonthisscaleusingthemicrometer.
6.Determinethedifferencebetweenthereadingstakeninstep3
andstep5.Ifthedifferenceis0.004”(0.10mm)orless,thehorizon‐
talcollimationiswithintolerance.Notethattheobservederroris4
timestheactualerror,soadifferenceof0.004”betweentheread‐
ingsindicatesa0.001”actualerrorat17feet,equatingtoone
arcsecond.
7.Ifanerrorisdetected,theinstrumentmaybeadjustedinthe
field.Locatethecapstanscrewsfurthestfromtheeyepiece,atthe3
o’clockand9o’clockpositions(Figure4.5).Usinganadjustingpin,
gentlyloosenoneandtightentheother,sothatapproximately1/4
oftheobservederrorisremoved.Beadvisedthattheslightest
movementmakesabigdifference.
Forexample,ifthereadinginstep3was3.402”,andthereadingin
step5was3.418”,thedifferencebetweenthereadingsis0.016”.
Therefore,wewanttomakeanadjustmentsothatthereticleap‐
pearstomove0.004”(one‐fourthof0.016”).Youcandothisby
movingthemicrometer
backtowardthefirstread‐
ing,settingiton(inthis
case)3.414”.Thisrepre‐
sentsamoveof0.004”back
towardstheoriginal3.402”
reading.Thiswillslightly
offsettheimagefromthe
scale’spairedlinetarget
currentlybeingviewed.
Then,adjustthereticleso
thatitappearstobecen‐
teredonceagain
onthe
scaletarget.
8.Repeatsteps2through7
untiltheerroriswithintol‐
erance.
Figure4.5
NOTE:Reticleorienta‐
tionislistedasaparame‐
teraffectedbythisadjust‐
ment.However,wedo
notaddressthattopic
herebecausegenerally,
minorfieldadjustments
ofthereticledon’tcause
thereticleorientationto
benegativelyaffected.
To Next Page