Telescope Eyepiece Calculator

Telescope Eyepiece Calculator is a professional, 100% offline tool for astronomers and serious stargazers. Enter your telescope aperture and focal length, pick an eyepiece (Plössl, Wide, UWA, Hyper, or custom), and instantly see magnification, exit pupil, true field of view (TFOV), and f-ratio: all with a clean, night-friendly design.

Why it’s useful • Choose the right eyepiece faster: live results as you type. • Avoid weak or mushy views: color badges warn about over/under magnification and tiny exit pupils. • Plan smarter sessions: see TFOV, power category (Low/Medium/High), and the effect of Barlow/Reducer multipliers.

Free Features • Telescope aperture & focal length (mm/inches) • Eyepiece focal length and type presets • Barlow/Reducer support with custom multipliers • Magnification, Exit Pupil, TFOV, f-ratio (real-time) • Power category (Low/Medium/High) • Night Mode + haptic feedback • One Equipment Case (save your default setup) • Works fully offline. No accounts. No tracking.

Pro Features (one-time upgrade) • Unlimited Cases: organize multiple telescopes & eyepieces • Side-by-Side Compare: evaluate two eyepieces at once • Precision Field-Stop TFOV: field-stop diameter for ultra-accurate TFOV • Quick Sets: one-tap telescope + Barlow combos • Premium Themes: Glass, AMOLED, Space Gray + adjustable haptics • PDF Export: share a clean session setup card • Smart Hints: color-coded warnings for over/under magnification

Built for iPhone and iPad with a crisp interface that’s easy on the eyes at the scope, whether you’re viewing planets, the Moon, or wide-field deep-sky objects.