Brunson 771 - Initial Setup and Leveling

Model 771, 75, and 76-RH190 Transits 8
intheverticalplane.The“flange”isthecomponentuponwhichthe
warningisprinted.Thissimplymeansnottorotatethetelescope
bygrabbingtheflangeandtwistingit.Torotatethetelescopeprop‐
erly,putyourhandonthetelescopebarrelitself.
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Loosenboththehorizontalandverticaltangentclampscrews.
Graspthestandardsfirmlywithonehand,andthebasewiththe
otherhand.Liftgentlyfromcaseandplaceonastandorothersup‐
port.Whilemaintainingaholdonthestandardswithonehand,
rotatethebasesothatthebottomplateisfirmlythreadedontoany
3½”–8externalthreadedmountorstand.Whenreplacingthe
transitintothecase,slightlytightenthehorizontalandverticaltan‐
gentclamplockscrews—butonlydosogently.
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Aspecialcenteringmount,differentthanmostofourinstrument
adapters,maybeemployedtophysicallyplacethehorizontalcen‐
terofthetransitinaknownlocation.Theshiftingcenterofthe
transitextendsaboveandbelowthebaseplate(visiblebetweenthe
levelingscrewsandalsofrombelowasa2”diameterringcentered
onthebottomofthebaseplate).Thisshiftingcenter(radius=1±
0.0001”)fitsintospecialmountshavinganaccuratelyboredinner
diameter.Ifthetransitistobelocatedononeofthesemounting
rings,thelevelingscrewsshouldbeloosenedslightlysothebase
platecanmovearoundinrelationtotheshiftingcenter.Re‐tighten
thelevelingscrewsonlyafterbaseplateistightenedonthemount.
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Oncemountedonastandorotherstableinstrumentmount,thefol‐
lowingprocesswill“rough‐level”thetransit,meaningthatthetran‐
sitwillbebroughtroughlytoplumb,andbewithin
rangeofthe
precisionlevelvialmountedalongthetelescopeaxis.
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Toroughlevel,loosenanytwoadjacentlevelingscrewsandturn
thefourarmʺspiderʺbasesothattwodiagonallyopposedleveling
screwsareinlinewiththeprincipalsightingdirectionthatwillbe
used.Figure2.2illustratesthis,
withthespiderbaselinedup
“square”withthetelescopeandcrossaxis.Re‐tightentheleveling
screws.
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Acircular“bull’seye”vialrestsonthehorizontal“plate”abovethe
basebutbelowthetelescopeaxis(Figure2.3).Wecallthisthe
“platevial”.Centerthisbubbleinthefollowingmanner:Puta
Removingfromthecase
Usingtheshiftingcenter
Roughleveling