Doublet glued objective lens refractive astronomical telescope DIY accessories diameter 30mm 31mm 32mm 34mm for DIY refractive achromatic telescope

Specification introduction, for example:
D31F120 blue film
Caliber: 31MM (actual outer diameter)
Focal length: 120 MM
Coating: Blue film coated

Suitable for DIY binoculars, viewing mirrors, star finder, etc.

Package List:
1* glued lens