Magnification of a Telescope Formula

Telescope Magnification

The magnification of a telescope is a measure of how much larger objects appear through the telescope compared to their size as seen with the naked eye.
It is an important feature when considering a telescope’s capabilities.
The magnification can be changed by using different eyepieces.

The formula for calculating the magnification of a telescope is: magnification = focal length of the telescope / focal length of the eyepiece.
In this formula, the focal length of the telescope is the distance (usually measured in millimeters) from the telescope’s primary lens or mirror to the point where the image is formed.
The focal length of the eyepiece is the distance (also usually measured in millimetres) from the eyepiece lens to the point where the light from the lens comes into focus.
By substituting different eyepiece focal lengths into the formula, you can calculate the various magnifications that a telescope can achieve.

While a high magnification can make faraway objects appear closer, the image can also become dimmer and less sharp, because the same amount of light is spread over a larger area.
The maximum useful magnification of a telescope is typically considered to be 50 times the diameter of the objective lens or mirror (measured in inches). Beyond this limit, images tend to become too dim and blurry to be useful.
The atmospheric conditions can also limit the usable magnification on a given night. Turbulence in the Earth’s atmosphere (known as “seeing”) can cause stars to twinkle and images to wobble, which becomes more noticeable at higher magnifications.

Understanding the magnification and how to calculate it from the focal lengths of the telescope and eyepiece can help you choose the right eyepieces for your observing needs. Remember, high magnifications are not always beneficial, and the conditions of observation are a crucial factor too.