The aperture indicates the diameter of the objective lens or the mirror.

Is the ratio of the aperture to the focal length of a telescope.

Specifies the width of the area through which light of certain wavelengths is allowed to pass. Light is blocked outside of this range.

The deflection optics with the eyepiece receiver also accommodate the blocking filter.

The optics’ field is illuminated without errors.

Many solar telescopes are also available with a Double Stack.

This is the distance between the objective lens or mirror and the focal point.

Light-gathering capacity of the telescope compared to the eye.

Describes the brightness of a star or point-shaped object, which can still just be distinguished by the telescope. The naked eye, for example, can make out stars with a magnitude of up to 6.

The telescope’s magnification should not exceed this factor, because otherwise the image will appear weak and dark.

The ability of the optic to discern the fine detail of objects that are close together.

Including eyepiece, but excluding dew cap.

Most telescopes are made of steel, aluminium or carbon fibre.

The weight of the tube is critical for the correct choice of mount.

There are basically two different types of telescope. A distinction is made between refractor (lens) and reflector (mirror) telescopes.

Describes the exact structure of the telescope thereby further subdividing the different types of telescope.