Telescope Eyepiece Calculator: Instantly Find the Right Eyepiece for Any Telescope
A free astronomy app that helps you choose the perfect eyepiece by calculating magnification, exit pupil, TFOV, and f-ratio in real time.
Magnification Power
Dark Mode
Equipment Cases
Eyepiece Compare
Quick Sets
Themes
Features with Benefits
Live Calculations: See magnification, exit pupil, TFOV, and f-ratio instantly.
Power Categories: Know at a glance whether your setup is best for planets, deep sky, or general use.
Barlow & Reducer Support: Apply multipliers to see the impact of accessories.
Dark/Light Mode: Comfortable viewing for day or night sessions.
Equipment Cases: Save unlimited telescopes and eyepieces for quick switching.
Eyepiece Compare: Evaluate two eyepieces side-by-side for smarter choices.
Field-Stop Precision: Get ultra-accurate TFOV with field-stop diameter inputs.
Quick Sets: Apply telescope + Barlow combos with a single tap.
Smart Hints: Avoid fuzzy or vignetted views with clear visual warnings.
How It Works
Telescope Eyepiece Calculator makes astronomy planning simple. Just enter your telescope’s aperture and focal length, then choose your eyepiece type (Plössl, Wide, UWA, Hyper, or Custom). The app instantly calculates magnification, exit pupil size, true field of view (TFOV), and f-ratio.
You’ll also see helpful power categories (low, medium, high) and color-coded hints if your setup is under- or over-magnified. Add a Barlow or reducer lens to instantly see how it changes your view.
For even more flexibility, upgrade to Pro: save unlimited equipment cases, compare two eyepieces side-by-side, unlock precision TFOV with field-stop calculations and apply Quick Sets with one tap. Everything works offline, with no accounts or tracking, just smooth astronomy calculations at your fingertips.
Frequently Asked Questions
💰 Pricing & Availability
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Yes, the app is free to download and use. You can calculate magnification, exit pupil, TFOV, and save one equipment case at no cost.
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For a one-time purchase of $5.99, you unlock unlimited equipment storage, eyepiece comparisons, precision field-stop TFOV, Quick Sets, premium themes and Smart Hints.
📱 Compatibility & Requirements
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The app is built for iPhone (iOS 17 and later). An iPad-optimized version may come in the future.
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No. The app works fully offline, ideal for remote observing sessions.
🔭 Features & Usage
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Magnification and exit pupil follow standard astronomy formulas. TFOV can be calculated quickly via AFOV or precisely using the field-stop method (Pro).
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Yes, with the Pro version you can run side-by-side comparisons showing magnification, exit pupil, and TFOV.
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They let you save telescopes and eyepieces for quick access. Free users get one default case, while Pro users can save unlimited setups.
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Quick Sets allow one-tap application of telescope + Barlow combinations, great for switching between configurations in the field.
🔒 Privacy & Security
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No. All data is stored locally on your iPhone. There are no accounts, no analytics, and no tracking.
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No login is required. You can use the app immediately after downloading.
⚙️ Settings & Customization
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Yes, you can toggle between metric and imperial units in Settings.
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Yes, there is a dark mode for stargazing and premium AMOLED/Glass themes for Pro users.
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Yes, just tap Restore Purchases in Settings and your Pro features will unlock again.