ASTRONOMY FOMULAE
Magnification
To determine the magnification of a telescope and eyepiece combina- tion, divide the telescope focal length be the eyepiece focal length.
Magnification (x) = Telescope Focal Length (mm)/Eyepiece Focal Length (mm)
Ex: 6.3mm Eyepiece with a 114x1000mm telescope.
Magnification = 1000mm/20mm
Magnification = 50x
Focal Ratio
To determine the focal ratio of a telescope, divide the focal length of the telescope by the aperture.
Focal Ratio (F/x)= Telescope Focal Length (mm)/Aperture (mm)
Ex: Focal Ratio of a 114x1000mm telescope.
Focal Ratio (F/x)= 1000mm/114mm
Focal Ratio (F/x)= F/8.8
Limiting Magnitude
To determine the limiting magnitude of a telescope, use the aperture in the following formula for an approximation.
Limiting Magnitude = 7.5 + 5LOG(Aperture in cm)
Ex: Limiting Magnitude of a 114x1000mm telescope.
Limiting Magnitude = 7.5 + 5LOG(11.4cm)
Limiting Magnitude = 7.5 + (5 x 1.057)
Limiting Magnitude = 12.785
Resolving Power
To determine the resolving power of a telescope under ideal conditions, divide the aperture into 4.56.
Resolving Power = 4.56/Aperture (in.)
Ex: Resolving Power of a 114x1000mm telescope.
Aperture (in.) = 114mm/25.4 = 4.49
Resolving Power = 4.56/4.49in.
Resolving Power = 1.02