Brunson 771 - Page 20

Model 771, 75, and 76-RH190 Transits 16
Alwayssetthetelescopeon
thefartargetbymak‐
ingangularmoves
usingthehorizontal
andverticaltangent
screw(s).

Alwayssetthetelescopeon
theneartargetby
makinglateralmoves
usingalateralslideor
precisionlift.
lateralshiftsoftheentireinstrumentarenotaseasy.Togreatly
simplifythis,werecommendtheuseofalateralslidemountedbe‐
tweenthetransitandthestandonwhichitismounted.

Stepstobuckthetransitintothetargetline:

1. Roughlypositionthetransit.Setuptheinstrument
standnominallyinlinewiththetwotargets.

2. Roughlevel.Roughlevelthetransitasdescribedin
Chapter2“RoughLeveling”.

3. Preciselevel.Formanyapplications,preciseleveling
yourtransitisrequiredpriortobuck‐in(coveredin
Chapter2).Technicallyisitpossibletobuckintotargets
withoutpreciseleveling,butthetransitwillnotendupin
theverticalplanedefinedbythosetargetsunlessthetran‐
sititselfispreciselyplumb.Afulldiscussionof
thisfactisbeyondthescopeofthismanual,butis
coveredinmoredetailinourOpticalTooling
classes.

4. Settofartarget.Focusthetelescopeonthefar
targetandsetthecrosswiresdirectlyoverthattar‐
getusingthehorizontaland/orverticaltangent
adjustmentscrews.Ifthetransitisbetweenthe
targets(asinFigure3.2),simplyassignoneofthe
targetstobethe“fartarget”,andsetonit.

5. Settoneartarget.Withoutmovingthehori‐
zontaltangentscreworturningthestandardsof
thetransit,turnthetelescopedownwardandfocus
onthesecondtarget.Notethatifthetransitislo‐
catedbetweenthetargets(asinFigure3.2),youwill
havetoturnthetelescope“through”the
standards
topointintheoppositedirection.Regardlessof
whetheryouareinasituationlikeFigure3.1or
Figure3.2,thissecondtargetwillinvariablybeoff
toonesideofthefieldofviewunlessyouarein‐
crediblylucky.Forpurposesofillustration,let’s
saythattheobservedlateraldistancetothenear
targetis“L”(seeFigure3.1or3.2).Nowyoumust
movethetransitlaterallytowardtheneartarget
usingthecrossslide—buthowmuch?The
amountthatyoumovethetransitdependsupon
thegeometryofthesetup.Theequationtocalcu‐
latethe
properamountofshiftis:

TransitLateralShift=Lx(D2/D1)

where

D1=Distancebetweentargets
Figure3.1