colors, so that it may safely be said, remembering that 

 wide aperture involves a greater amount of color, that 

 an objective showing the proper colors of green and 

 purple and having proper resolving power may safely 

 be accepted, or in the choice of objectives between one 

 showing no color but having no resolving power, the 

 other having color and resolving power, the latter is 

 certainly the preferable one. 



When colors of green and purple are not sufficiently 

 pronounced on an object when the mirror is in central 

 position, they will become more apparent when the 

 mirror is swung to an oblique position, using any object 

 suitable to the power of the objective, and preferably 

 mounted dry. 



If the mirror is swung to the left, the object should 

 be fringed on the right side with yellow-green and on 

 the left with bluish color, or if the mirror is swung 

 to the right the conditions are reversed. 



When the objective is not properly corrected it is 

 said to be chromatically under-corrected or over-corrected. 



It is well to state here, however, that, with the care 

 which is exercised by reputable makers, objectives 

 which deviate from the proper point of correction, or in 

 which the under- or over-correction is so prominent 

 as to be noticeable to one inexperienced in this work, 

 are never allowed to reach the public. These remarks 

 are not intended to discourage the student from testing 



86 



