Abstract:
A four-component eyepiece for an optometer has an eye relief of about 117mm and is substantially free of chromatic aberration.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an eyepiece and more particularly to an optometer eyepiece having four components. 
    
    
     THE DRAWING 
     FIG. 1 is an optical diagram of an eyepiece viewed transverse to the optical axis. 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, an optometer eyepiece is diagrammatically shown with optically-aligned lenses I, II, III and IV. The first component I is a biconcavo negative singlet, the second component II is a plano-convex positive singlet, the third component III is a biconvex positive singlet and the fourth component IV is a biconvex positive doublet. The eyepiece provides an imaging distance providing an eye relief of about 117mm. 
     The parameters of the eyepiece according to the present invention are set forth in Table I with axial thicknesses of successive lens components designated T 1  to T 5  and the successive axial spaces from the first component of the eyepiece to the observer&#39;s eye are designated S 1  to S 4 . The successive lens radii are designated R 1  to R 9  with a minus sign (-) indicating surfaces whose center of curvature lies on the eye side of their vertices. Refractive indices and Abbe numbers of the glasses in the successive lenses are absolute values designated ND 1  to ND 5  and ν 1  to ν 5  respectively. 
     
                                           Table I__________________________________________________________________________                      Index of AbbeLens   Radius(R)      Thickness(T)              Spacing(S)                      Refraction(ND)                               No.(ν)__________________________________________________________________________   R.sub.1 =+0.90598xI          T.sub.1 =0.034188x                      1.58&lt;ND.sub.1 &lt;1.60                               ν.sub.1 ≅61   R.sub.2 =-0.90598x              S.sub.1 =0.28222x   R.sub.3 = &gt; 100xII         T.sub.2 =0.051282x                      1.58&lt;ND.sub.2 &lt;1.60                               ν.sub.2 ≅61   R.sub.4 = 1.6036x              S.sub.2 =0.0008547x   R.sub.5 =-1.5231xIII        T.sub.3 =0.068376x                      1.58&lt;ND.sub.3 &lt;1.60                               ν.sub.3 ≅61   R.sub.6 = 0.89786x              S.sub.3 =0.17239x   R.sub.7 =-1.8352x      T.sub.4 =0.08547x                      1.58&lt;ND.sub.4 &lt;1.60                               ν.sub.4 ≅61IV R.sub.8 = 0.42966x      T.sub.5 =0.059829x                      1.77&lt;ND.sub.5 &lt;1.79                               ν.sub.5 ≅26   R.sub.9 = 1.1479x              S.sub.4 =0.9982xwherein x is 115 to 119mm.__________________________________________________________________________ 
    
     A specific embodiment of the present invention wherein x is equal to 117mm and has the following values with radii, spacings and thicknesses being in millimeters. 
     
                                           Table II__________________________________________________________________________                      Index of AbbeLens   Radius(R)      Thickness(T)              Spacing(S)                      Refraction(ND)                               No.(ν)__________________________________________________________________________   R.sub.1 = 106.00I          T.sub.1 = 4.0   ND.sub.1 =1.589                               ν.sub.1 =61.12   R.sub.2 =-106.00              S.sub.1 =33.02   R.sub.3 = ∞II         T.sub.2 = 6.0   ND.sub.2 =1.589                               ν.sub.2 =61.12   R.sub.4 = 187.62              S.sub.2 = 0.10   R.sub.5 =-178.20III        T.sub.3 = 8.0   ND.sub.3 =1.589                               ν.sub.3 =61.12   R.sub.6 = 105.05              S.sub.3 =20.17   R.sub.7 =-214.715      T.sub.4 =10.0   ND.sub.4 =1.589                               ν.sub.4 =61.12IV R.sub.8 =  50.27      T.sub.5 = 7.0   ND.sub.5 =1.784                               ν.sub.5 =25.76   R.sub.9 =134.30              S.sub.4 =116.79__________________________________________________________________________