In the Bausch & Lomb instrument, the diaphragm adjusting 

 studs are concealed beneath a ferrule which forms a guard against 

 accident or tampering as well as an additional protection against 

 moisture. Remove the ferrule to adjust the diaphragm as suggested. 

 If the eyepiece is of the erecting type, move the diaphragm in the 

 direction opposite the one which seems to be necessary; but if the 

 ocular is of the inverting type, it will give a positive image of the 

 field and the diaphragm may be moved in the direction apparently 

 necessary. 



The supreme test of the accuracy of the draw-tube and the 

 capacity of the instrument to perform accurate work at all distances 

 in the field, now requires that the collimation adjustment shall be 

 repeated on a point not over 12 to 15 feet from the instrument. 

 This necessitates racking out the focusing system, by which any 

 lateral displacement will be plainly manifest on inverting the tele- 

 scope. When a condition of this kind exists, the mean of double 

 observations should be taken or the matter should be reported to 

 the manufacturer. 



In the example suggested in Figure 2, a side adjustment for 

 the vertical wire should be secured mid-way between the two outside 

 positions; but it is not so important in a level as the proper location 

 of the horizontal wire. A level would work successfully without 

 a vertical wire, but it is always convenient for reference in plumbing 

 the rod. 



It is very desirable that the horizontal wire shall be truly hori- 

 zontal over the entire span of the field. When all the adjustments 

 are completed, as accomplished by the following directions, and 

 the vertical axis adjusted to perfect verticality, close the clips and 

 revolve the instrument slightly from side to side while sighting on 

 a test point. If the point appears to rise above the horizontal wire 

 at one end and drop below at the other, all the studs of the dia- 

 phragm should be loosened and one of them tapped gently in the 

 direction desired. This process may slightly disturb the adjustment 

 for collimation, and in this event the collimation test should be re- 

 peated. 



If the Eyepiece is not perfectly centered, the collimated cross 

 wires may not appear to be in the exact center of the field of view, 

 but this state of affairs need cause no apprehension. If the cross 

 wires and the field of view appear to move around in a small circle, 

 eccentricity in mounting is evident; but if the cross adheres to the 

 test point on inversion, the utmost requirements in the case have 

 been fulfilled and the further rectification can only be accompli shed 

 by aligning the axis of the eyepiece with that of the objective, 



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