What is a Telescope's Field of View? (A Simple Guide)

When you look through a telescope, the little circle of sky you see is your **Field of View**. Think of it like looking through a porthole on a spaceship. A wide field of view is a giant panoramic window, letting you see huge swathes of the cosmos at once. This is perfect for stargazing, spotting vast star clusters like the Pleiades, or finding your way around the constellations. A narrow field of view, on the other hand, is like zooming in with a powerful camera lens. The window becomes tiny, but you see incredible, magnified detail inside it. This is what you need for getting a close-up look at the craters on the Moon, the rings of Saturn, or the swirling arms of a distant galaxy. The perfect view depends entirely on your target.

This calculator is designed to be your personal mission control, helping you figure out exactly what your "porthole" will look like before you even step outside. It does all the important math for you by looking at your telescope's specifications and the eyepiece you're using. It instantly tells you your **Magnification** (how "zoomed in" you are) and your **True Field of View** (the actual size of your window on the sky). But it doesn't stop there. It also calculates your telescope's **Focal Ratio** (its "speed" for photography) and the **Exit Pupil** (the little beam of light that enters your eye, which tells you how bright the image will be). The visualizer even shows you how your view compares to famous celestial objects, giving you a real, intuitive sense of scale. It's about taking the guesswork out of stargazing so you can spend more time enjoying the wonders of the night sky.

How to Use the Calculator

Finding your telescope's viewing properties is an easy process:

1. Choose Your Mode: Use the tabs at the top to select what you want to calculate. "Calculate View" is for finding the stats of an eyepiece you own. "Find Eyepiece" is for figuring out what eyepiece you need to buy to hit a specific magnification.
2. Enter Your Telescope's Specs: Start by entering your telescope's **Focal Length** and **Aperture** in millimeters. You can also choose a common telescope from the "Load Preset" menu to fill this in for you.
3. Enter Your Eyepiece or Target Mag: Depending on the mode, either enter the details of the eyepiece you're using, or enter the target magnification you want to achieve.
4. See Your Results Instantly:** All the calculations and the visualizer will update in real-time as you enter your numbers. You'll see your final magnification, true field of view, and more, giving you a complete picture of your setup.