Rayleigh and Dawes resolution
Resolving power (or resolution) of an optical telescope is the ability to see small details in the image. It is an angular distance between two… Read More »Rayleigh and Dawes resolution
Telescopes
Barlow lens
Magnification of telescopes is calculated by dividing the objective focal length with the eyepiece focal length. To change the magnification, a different eyepiece must be… Read More »Barlow lens
Aperture, focal length and focal ratio
Aperture One of the essential features of a telescope is its aperture. Depending on the type of telescope, the aperture can be either a lens… Read More »Aperture, focal length and focal ratio
Lowest and highest useful magnification
Magnification is the ability of a telescope to magnify an object. A lot of observers, not only beginners, don’t understand why higher magnification often doesn’t… Read More »Lowest and highest useful magnification
Light gathering power
The light gathering power (also light grasp) is an ability of a telescope to collect more light than the human eye. It is expressed as… Read More »Light gathering power
Limiting magnitude – calculations
In astronomy, the magnitude refers to a logarithmic measure of the brightness of a celestial body. The larger the magnitude number, the fainter the object.… Read More »Limiting magnitude – calculations
Secondary mirror
A secondary mirror is a small mirror element in reflectors and catadioptric telescopes. It is used to bounce the light gathered by the primary mirror… Read More »Secondary mirror
Finderscope
A finderscope is a device found on top of a primary telescope. It is used for manually aiming the telescope to the desired celestial object.… Read More »Finderscope
Tracking
Tracking is a phrase in astronomy, which means that a telescope sited on mount can follow the object as it moves on the night sky.… Read More »Tracking
Guiding
With a motor-driven mount, it is essential to know all astronomy terms. The difference between the terms tracking and guiding can be very confusing for… Read More »Guiding