An apochromatic design is given for a 4 inch f/10 telescope objective that consists of a cemented triplet with the middle lens being equi-convex.

1. David Shafer Optical Design
Fairfield, CT 06824
203-259-1431
shaferlens@sbcglobal.net
Cemented apochromatic triplet telescope objective

2. This is a design for a 4 inch
f/10 telescope objective
that is well corrected for a
wide spectral region. It uses
one anomalous dispersion
glass and two ordinary glass
types. The low dispersion
Ohara glass FPL51 is key to
the good color correction.
Ohara FPL53 glass has even
lower dispersion but is
substantially more
expensive and has inferior
chemical and hardness
qualities compared to FPL51
The central lens of Ohara FPL51 glass has the
same radius on both sides.

3. Radius thickness semi-aperture glass
1 552.153099 8.000000 52.000000 BK7
2 241.117587 16.000000 52.000000 S-FPL51
3 -241.117587 8.000000 52.000000 K7
4 -2.4715e+03 982.000000 52.000000 AIR
Image radius -377.411699
Design data is in mm. 100 mm aperture diameter, 1000 mm focal length. On a curved
image it has a polychromatic (.4358u to .7000u) wavefront error of about .06 waves
r.m.s. at the edge of a 1.0 degree diameter field.