The "12" in your query likely refers to a . In refractor building, a longer focal ratio like f/12 is often recommended for beginners because it:
Using methods like the Ronchi test or Foucault test to ensure the lens surface is a perfect sphere or parabola. making a refractor telescope norman remer pdf 12 new
Variant 3 — Intermediate 80/600 Apochromat Lite The "12" in your query likely refers to a
Usually machined from aluminum or high-density plastics. making a refractor telescope norman remer pdf 12 new