Compute the angular magnification of a refracting telescope from objective and eyepiece focal lengths.
由物镜与目镜焦距,按 M = f₀/fₑ 计算望远镜角放大率。
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Magnification | M = f_objective ÷ f_eyepiece for Keplerian and Galilean | Basic telescope optics |
| Useful magnification limit | Useful limit ≈2×D(mm); beyond it, the exit pupil shrinks below 0.5 mm | Amateur-astronomy rule of thumb |
| Exit pupil | Exit pupil = D ÷ M; 5–7 mm matches the dark-adapted eye | Eyepiece-design practice |
| Resolution link | Magnification is capped by Rayleigh θ=1.22λ/D; it only enlarges the Airy disk | Rayleigh criterion application |