Is this calculation free and private?

Yes, 100% of calculations execute locally in your web browser. No inputs or personal data are stored or transmitted.

What does the Telescope Magnification & Exit Pupil Calculator give me?

It works out Magnification Power, Exit Pupil Diameter, Focal Ratio and True Field of View in Sky, updating live as you change the inputs.

What do I need to enter?

Just Telescope Primary Aperture, Telescope Focal Length, Eyepiece Focal Length and Eyepiece Apparent FOV. Every field has a sensible default you can start from.

Is my data uploaded anywhere?

No. The calculation runs in your browser with JavaScript — nothing you type is sent to a server or stored.

Does it work on a phone?

Yes. The layout adapts to small screens and needs no app or signup.

Telescope Magnification & Exit Pupil Calculator

Calculate astronomical telescope magnification (x), exit pupil diameter (mm), focal ratio (f-number), and maximum theoretical power.

100% free
Private in browser
No signup
No watermarks

Telescope Primary Aperture (mm, e.g. 200mm=8")

Telescope Focal Length (mm)

Eyepiece Focal Length (mm)

Eyepiece Apparent FOV (°: 52 Plossl, 68 Wide, 82 Ultra)

Magnification Power (x)

100

Exit Pupil Diameter (mm)

Focal Ratio (f-number)

True Field of View in Sky (° TFOV)

0.52

Rate this tool

Be the first to rate — helps others and improves this page.

About Telescope Magnification & Exit Pupil Calculator

Calculate astronomical telescope magnification (x), exit pupil diameter (mm), focal ratio (f-number), and maximum theoretical power. Enter Telescope Primary Aperture, Telescope Focal Length and Eyepiece Focal Length and the tool works out Magnification Power, Exit Pupil Diameter and Focal Ratio straight away. Everything runs in your browser, so your data never leaves your device.

How to use Telescope Magnification & Exit Pupil Calculator

Enter Telescope Primary Aperture, Telescope Focal Length and Eyepiece Focal Length.
Adjust the remaining options (Eyepiece Apparent FOV) to match your case.
Read Magnification Power, Exit Pupil Diameter and Focal Ratio in the results panel — copy or download what you need.

Key features

Shows Magnification Power (x)
Shows Exit Pupil Diameter (mm)
Shows Focal Ratio (f-number)
4 adjustable inputs, results update as you type
No signup, no limits

Frequently asked questions

Is this calculation free and private?: Yes, 100% of calculations execute locally in your web browser. No inputs or personal data are stored or transmitted.
What does the Telescope Magnification & Exit Pupil Calculator give me?: It works out Magnification Power, Exit Pupil Diameter, Focal Ratio and True Field of View in Sky, updating live as you change the inputs.
What do I need to enter?: Just Telescope Primary Aperture, Telescope Focal Length, Eyepiece Focal Length and Eyepiece Apparent FOV. Every field has a sensible default you can start from.
Is my data uploaded anywhere?: No. The calculation runs in your browser with JavaScript — nothing you type is sent to a server or stored.
Does it work on a phone?: Yes. The layout adapts to small screens and needs no app or signup.

Related In-Depth Guides

Learn practical workflows, real-world examples, and expert tips in our comprehensive guides:

Home Renovation & DIY · 8 min read