What AFOV do common eyepiece types have?

Plossl: 50-52°, Erfle/wide-angle: 65-68°, Nagler/ultra-wide: 82°, Ethos: 100°.

How do I find objects in a narrow FOV?

Use a lower magnification eyepiece (wider TFOV) to locate objects, then switch to higher magnification for detail.

Does the true FOV change with a Barlow?

Yes. A 2× Barlow doubles the magnification, halving the true field of view.

Free Field of View Calculator

Calculate the true field of view of a telescope and eyepiece combination: TFOV = AFOV / Magnification.

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Apparent FOV of Eyepiece

Objective Focal Length

Eyepiece Focal Length

True Field of View

1.083 °

Magnification48.0 ×

True FOV (arcmin)65.0 '

True Field of View vs Apparent FOV of Eyepiece

View formula & how it works →

True Field of View

TFOV = AFOV / Magnification

The apparent field of view (AFOV) is a property of the eyepiece design (e.g., 52° for Plossl, 68° for wide-angle, 82° for ultra-wide). Dividing by magnification gives the actual sky patch visible.

The full Moon is about 0.5° across, useful as a reference.

Example Calculation

52° AFOV eyepiece at 48×.

01Magnification = 1200 / 25 = 48×
02TFOV = 52 / 48 = 1.083° = 65.0 arcmin
03This fits about two full Moons side by side.

Frequently Asked Questions

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