Telescope Magnification Calculator
Calculate telescope magnification and optical performance parameters for astronomy observations
Calculate Telescope Magnification
Telescope Characteristics
Diameter of the primary mirror or lens
Ratio of focal length to diameter (e.g., f/8)
Eyepiece Parameters
Focal length of the eyepiece
Angular field of view of the eyepiece (typically 52°)
Magnification Results
Main Formula: Magnification (M) = Telescope Focal Length (fo) ÷ Eyepiece Focal Length (fe)
F-Ratio: f/0 = 0mm ÷ 0mm
Magnification Analysis
Example Calculation
8-inch SCT with 25mm Eyepiece
Telescope: 8" Schmidt-Cassegrain (203mm diameter, f/10)
Focal Length: 203mm × f/10 = 2030mm
Eyepiece: 25mm focal length, 52° apparent FOV
Magnification: 2030mm ÷ 25mm = 81.2×
Calculated Properties
Resolving Power: 115.8" ÷ 203mm = 0.57"
Exit Pupil: 203mm ÷ 81.2× = 2.5mm
Field of View: 52° ÷ 81.2× = 0.64°
Star Limit: 2 + 5×log(203) = 13.5 mag
Magnification Guidelines
Common Telescope Types
Observation Tips
Start with lowest magnification to find objects
Exit pupil should be 1-7mm for best viewing
Use high magnification for lunar and planetary details
Low magnification shows more of extended objects
Atmospheric seeing limits useful magnification
Understanding Telescope Magnification
How Telescopes Work
A telescope consists of an objective (primary mirror or lens) that collects light and an eyepiece that magnifies the image. The objective's focal length and diameter determine the telescope's basic characteristics, while the eyepiece allows you to adjust magnification.
Key Concepts
- •F-ratio: Focal length divided by diameter (e.g., f/8 = 800mm/100mm)
- •Exit pupil: Diameter of light beam exiting the eyepiece
- •Resolving power: Ability to distinguish fine details
Magnification Formula
Magnification = Telescope Focal Length ÷ Eyepiece Focal Length
M = fo ÷ fe
Additional Formulas
Resolving Power: Pr = 115.8" ÷ Do (in mm)
Exit Pupil: Dep = Do ÷ M
Field of View: FOVs = FOVe ÷ M
F-ratio: fr = fo ÷ Do
Star Limit: Lm = 2 + 5×log(Do)
Tip: Higher magnification doesn't always mean better views. The atmosphere and telescope quality limit useful magnification to about 2× the diameter in mm.
Magnification vs Object Type
Planets
High magnification (150-300×) shows surface details and moons
Deep Sky Objects
Low-medium magnification (30-100×) for galaxies and nebulae
Double Stars
High magnification (200-400×) to separate close pairs
Factors Affecting Performance
Atmospheric Seeing
Limits effective magnification, varies by location and conditions
Telescope Quality
Better optics can handle higher magnifications effectively
Eye Pupil Size
7mm in dark, 2-3mm in bright conditions, affects optimal exit pupil