( 6 ) 



I. Numerical Aperture Table. 



The " Aperttjbe" of an optical Instrument indicates its greater or less capacity for receiving rays from the object and 

 transmitting them to the image, and the aperture of a Microscope objective is therefore determined by the ratio 

 between its focal length and the diameter of the emergent pencil at the plane of its emergence— that is, the utilized 

 diameter of a single-Iens objective or of the back lens of a compound objective. 



This ratio is expressed for all media and in all cases by n sin m, n being the refractive index of the medium and u the 

 semi-angle of apsrture. The value of n sin u for any particular case is the " numerical aperture " of the objective. 



Diameters of the 

 Back Lenses of various 



Dry and Immersion 

 Objectives of the same 



Power (i in.) 

 from 0-50 to 1-52 N. A. 



Numerical 

 Aperture. 



(n sin w = a.) 



•53 

 •50 

 •48 

 •46 

 •44 

 •42 

 •40 

 •38 

 •36 

 •34 

 •33 

 •32 

 •30 

 •28 

 •26 

 •24 

 •22 

 •20 

 •18 

 •16 

 •14 

 •12 

 •10 

 •08 

 •06 

 •04 

 •02 

 •00 

 •98 

 •96 

 •94 

 •92 

 •90 

 •88 

 •86 

 •84 

 •82 

 •80 

 •78 

 •76 

 •74 

 •72 

 •70 

 •68 

 •66 

 •64 

 •62 

 •60 

 •58 

 •58 

 •64 

 •52 

 •50 



Angle of Aperture (= 2 u). 



Dry 



Objectives. 



in = 1.) 



180° 0' 



157° 2' 



147° 29' 



140° 6' 



133° 51' 



128° 19' 



123° 17' 



118° 38' 



114° 17' 



110° 10' 



106° 16' 



102°. 31' 



98° 56' 



95° 28' 



92° 6' 



88° 51' 



85° 41' 



82° 

 79° 

 70° 

 73° 



36' 

 35' 

 38' 

 44' 



70° 54' 



68° 6' 



65° 22' 



62° 40' 



60° 0' 



Water- Homogeneous- 

 Immersion', Immersion 

 Objectives. Objectives. 

 (»i = l-33.) (n = 1-52.) 



Illumi- 

 nating 

 Power. 

 (a2.) 



Theoretical 



Resolving 



Power, in 



Lines to an Inch 



(A.=0'6269/«, 



=line E.) 



180° 0' 



165° 56' 



155° 38' 



148° 28' 



142° 39' 



137° 36' 



133° 4' 



128° 55' 



125° 3' 



121° 20' 



118° 00' 



114° 44' 



111° 36' 



108° 36' 



105° 42' 



102° 53' 



100° 10' 



97° 31' 



94° 56' 



92° 24' 



89° 56' 



87° 32' 



85° 10' 



82° 51' 



80° 34' 



78° 20' 



76° 8' 



73° 58' 



71° 49' 



69° 42' 



67° 36' 



65° 32' 



63° 31' 



61° 30' 



59° 30' 



57° 31' 



55° 34' 



53° 38' 



51° 42' 



49° 48' 



47° 54' 



46° 2' 



44° 10' 



180° 0' 



161° 23' 



153° 39' 



147° 42' 



142° 40' 



138° 12' 



134° 10' 



130° 26' 



126° 57' 



123° 40' 



122° 6' 



120° 33 



117° 34' 



114° 44' 



111° 59' 



109° 20' 



106° 45' 



104° 15' 



101° 50' 



99° 29' 



97° 11' 



94° 56' 



92° 43' 



90° 33' 



88° 26' 



86° 21' 



84° 18' 



82° 17' 



80° 17' 



78° 20' 



76° 24' 



74° 30' 



72° 36' 



70° 44' 



68° 54' 



67° 6' 



65° 18' 



63° 31' 



61° 45' 



60° 0' 



58° 16' 



50° 32' 



54° 50' 



53° 9' 



51° 28' 



49° 48' 



48° 9' 



46° 30' 



44° 51' 



43° 14' 



41° 37' 



40° 0' 



38° 24' 



146,528 



144,600 



142,672 



140,744 



138.816 



136,888 



134,960 



133,032 



131,104 



129,176 



128,212 



127,248 



125,320 



123,392 



121,464 



119,536 



117,608 



115,680 



113,752 



111,824 



109,896 



107,968 



106,040 



104,112 



102,184 



100,256 



98,328 



96,400 



94,472 



92,544 



90,616 



88,688 



80,760 



84,832 



82,904 



80,976 



79,048 



77,120 



75,192 



73,264 



71,336 



69,408 



67,480 



65,552 



63,624 



61,696 



59,768 



57,840 



55,912 



63,984 



52,056 



50,128 



48.200 



Example. — The apertures of four objectives, two of which are dry, one water-immersion, and one oil-immersion, 

 would be compared on the angular aperture view as follows: — 106° (air), 157° (air), 142° (water), 130° (oil). 



Their actual apertures are, however, as '80 '»S 1-26 1-38 or their 



uuzuQclcal apertures. 



