Optical magnification formulas
For compound microscopes: Total Magnification = Objective Power × Eyepiece Power. Field of View diameter = Field Number (FN) / Objective Power.
For telescopes: Magnification = Focal Length of Objective / Focal Length of Eyepiece. Exit Pupil = Aperture / Magnification.
For thin lenses: 1/f = 1/do + 1/di, where magnification M = |di / do|.
Worked example: Compound microscope inspection
Using a 40x high-dry objective with standard 10x wide-field eyepieces (FN 20mm) produces 400x total magnification.
The visible field of view diameter on the specimen slide is 20 / 40 = 0.50 mm (500 micrometres).
Magnification calculator inputs
Optical System
Select compound microscope, astronomical telescope, or thin lens.
CALCULATOR QUESTIONS
Optics & telescope magnification calculator questions
What is the maximum useful magnification of a telescope?
The practical maximum useful magnification is approximately 2x per millimetre of aperture (or 50x per inch) under ideal atmospheric conditions.
What does a 40x objective and 10x eyepiece give?
Multiplying objective power by eyepiece power gives 40 × 10 = 400x total magnification.