Doublet F.L.  mm     Doublet Type 
 
Front Lens                Rear Lens     
N1 l1   nm       N1 l1   nm
N2 l2   nm       N2 l2   nm
N3 l3   nm       N3 l3   nm
R1 R2 mm      R3 R4 mm
 
Here are possible two type of calculations:

1. Using glass catalog data; Enter doublet focal length, select a glass type for both front and rear lens from the Schott glass catalog (for example BK7 and F2). This will fill with data, the refractive indices fields N1, N2, N3 for a fixed wavelengths and finally press the "Calc" button.

2. Using user defined indices and wavelengths; Specify the doublet's focal length. Enter three refractive indices N1, N2, N3 and correspond wavelengths l1, l2, l3 for both front and rear doublet's lens and finally press the "Calc" button.

Note: This calculator is Java Script version of a BASIC program written by John A. Church in "Designing an Aplanatic Doublet" page 450 of the November 1984 issue of Sky and Telescope magazine.