It combines the advantages of refractor and reflector: large field of view, good image quality, short lens barrel, and easy portability. There are two types: Schmidt-Cassegrain and Marksutov-Cassegrain.

Two, common astronomical telescope optical terms

Aperture: refers to the effective diameter of the objective lens of the telescope, and the size of the aperture directly determines the performance of the telescope. The larger the aperture, the stronger the light-gathering ability, the higher the resolution, and the larger the available magnification.

Focal length: The distance from the objective lens to the focal point, generally expressed as "f", and the unit is mm.

Focal ratio: refers to the ratio of the focal length of the telescope to the diameter of the objective lens. Simply put, it is the length of the lens barrel divided by the diameter of the lens barrel, which is equivalent to the aperture on the camera lens. Indicated by "F".

Calculation formula: focal length/diameter = focal ratio (F=F/d). For example: Pioneer 60/700 telescope, focal ratio=objective focal length 700mm/objective aperture 60mm=11.7. If the aperture remains the same, the longer the focal length of the objective lens, the larger the focal ratio, and the higher the magnification can be easily obtained; the shorter the focal length of the objective lens, the smaller the focal ratio, it is not easy to obtain a higher magnification, but the image is brighter and the field of view is larger.

*Short focal length lens (small focal ratio, focal ratio <=6): suitable for observing nebulae and looking for comets;

*Telephoto lens (large focal ratio, focal ratio>15): suitable for observing the moon and planets;

*Medium focal length lens (medium focal ratio, 6

Magnification (magnification): the ratio of the focal length of the objective lens to the focal length of the eyepiece, such as the pioneer 60/700 astronomical telescope, using H10mm eyepiece, the magnification = the focal length of the objective lens 700mm / the focal length of the eyepiece 10mm = 70 times; the magnification becomes larger, the image you see also bigger. The appropriate high magnification should be ten times the diameter of the main mirror (calculated in centimeters), and the maximum is limited to fifteen times. For example: the highest magnification of Celestron 60AZ is: 60*1.5=90.

Optical axis: The axis of the light path in a telescope. The optical axis is skewed, which affects the imaging effect.

Coating: A special metal compound coated on the surface of the lens to increase the light transmittance.

Polar axis telescope: The line connecting the north and south poles of the celestial sphere is called the polar axis. The function is to correct the right ascension axis of the equatorial mount.

Right Ascension Axis: The axis of rotation in an equatorial mount that is parallel to the polar axis.

Declination axis: The axis of rotation in an equatorial mount that is perpendicular to the polar axis.

Weight: installed at the bottom of the declination axis, can be adjusted up and down, used to balance the weight of the telescope.

Dial: There are dials on the right ascension axis and the declination axis, which are generally for reference only.

Automatic import: Some high-end equatorial mounts have a built-in small computer, and store many celestial body position data, as long as the name of the celestial body is entered from the control panel, the equatorial mount will automatically search for the celestial body and import it into the telescope's field of view.

Gathering power: refers to the ratio of the amount of light collected by a telescope to that of the naked eye. Simply put, it is equal to the diameter of the telescope (cm) divided by the square of 7. The larger the aperture of the telescope, the stronger the light-gathering power, and the fainter celestial objects can be observed. For example: Celestron 70EQ telescope, collecting power = objective aperture 70/7×70/7=100. Generally, the larger the aperture of the primary mirror, the better the relative light-gathering power and the better the imaging quality.

Resolution energy: also known as resolution force (θ). The ability of a telescope to resolve image details, and the resolution is mainly related to the aperture. The larger the effective aperture of the objective lens, the better its decomposition ability and the more detailed the image.

Chromatic aberration: When a telescope is viewing an object, there are usually rainbow-like colors around the image, usually blue, red, or purple. This phenomenon is called chromatic aberration.

Aberration: When a telescope is viewing an object, the central part of the field of view is usually clear, but the periphery of the field of view is blurred or the image is distorted. This phenomenon is called aberration.

Field of view (field of view): refers to the size of the range seen by the telescope, expressed in degrees. Generally, the larger the eyepiece aperture, the larger the field of view. Eyepieces with a wide field of view are more comfortable to observe.

Limit magnitude (M): The dimest magnitude that the telescope can see is called the limit magnitude, which is mainly related to the aperture and focal ratio. Calculation formula: limit magnitude (M)=1.77+5㏒ (objective lens diameter). For example: a telescope with an objective lens diameter of 70mm, the limit magnitude (M)=1.77+5㏒70=11.0 etc.