There are lot, depending on your requirements. Anyway you can try: yil{RfBEr_
GbNVcP.ocP
1, Refractive: an achromatic as positive + plano-convex as negative; jkPXkysm
OR Ye(0'*-jyc
2, Reflective: two parabolic mirrors; ;%U`lE0
P^1rNB
Both of them affer nice spherical aberration performance. gk]r:p<