Tag: astrophotography

If you are interested in buying a telescope, you might have come across two types of mounts: the altitude azimuth mount (also known as alt-az or AZ) and the equatorial mount (also known as EQ). These mounts are the parts that support the optical tube of the telescope and allow it to move and point at different objects in the sky. But what are the differences between these two mounts, and which one is better for your needs? In this blog post, we will compare the altitude azimuth mount and the equatorial mount in terms of their design, advantages, disadvantages, uses and coordinate systems. By the end of this post, you will have a better understanding of these mounts and be able to make an informed decision.

What is an Altitude Azimuth Mount?

An altitude azimuth mount is a simple and intuitive type of mount that allows the telescope to move in two directions: up and down (altitude) and left and right (azimuth). The azimuth axis is perpendicular to the ground, while the altitude axis is parallel to the ground. This type of mount mimics how we perceive the world around us, as we use compass points (azimuth) and angles above the horizon (altitude) to locate objects.

An altitude azimuth mount can be manual or motorized, depending on whether you want to control the movement of the telescope by hand or by a remote controller. Some altitude azimuth mounts are also computerized, meaning that they have a built-in database of celestial objects and can automatically point the telescope at them with a push of a button.

Some common types of altitude azimuth mounts are:

• Fork mount: This mount has two arms that hold the optical tube on both sides. It is usually used for catadioptric telescopes, such as Schmidt-Cassegrains or Maksutov-Cassegrains.
• Yoke mount: This mount has a single arm that holds the optical tube on one side. It is usually used for small refractors or reflectors.
• Dobsonian mount: This mount is a special type of altitude azimuth mount that consists of a wooden box with a rotating base and a cradle for the optical tube. It is usually used for large Newtonian reflectors.

What is an Equatorial Mount?

An equatorial mount is a more complex and sophisticated type of mount that allows the telescope to move in two directions: right ascension (RA) and declination (DEC). The RA axis is aligned with the Earth’s rotational axis, while the DEC axis is perpendicular to it. This type of mount follows how celestial objects move across the sky, as they appear to rotate around the celestial poles due to the Earth’s rotation.

An equatorial mount can be manual or motorized, depending on whether you want to control the movement of the telescope by hand or by a remote controller. Some equatorial mounts are also computerized, meaning that they have a built-in database of celestial objects and can automatically point the telescope at them with a push of a button.

Some common types of equatorial mounts are:

• German equatorial mount: This mount has a counterweight on one end of the RA axis and the optical tube on the other end. It is usually used for refractors or small reflectors.
• Fork equatorial mount: This mount has two arms that hold the optical tube on both sides, but unlike the fork alt-az mount, it has an additional wedge that tilts the whole assembly to align with the Earth’s rotational axis. It is usually used for catadioptric telescopes.
• Horseshoe equatorial mount: This mount has a U-shaped structure that holds the optical tube on one side and allows it to move freely around the RA axis. It is usually used for large reflectors.

Advantages and Disadvantages of Altitude Azimuth Mounts

Altitude azimuth mounts have some advantages and disadvantages compared to equatorial mounts. Here are some of them:

Advantages

• They are easy to set up and use, as they do not require polar alignment or balancing.
• They are cheaper than equatorial mounts, as they have fewer parts and less precision.
• They can handle heavier telescopes, especially Dobsonian mounts, which are very stable and sturdy.
• They are sufficient for planetary and lunar observation and imaging, as these objects do not move very fast across the sky.

Disadvantages

• They are not suitable for deep-sky observation and imaging, as these objects move faster across the sky and require constant adjustment in both axes, which can be tedious and inaccurate.
• They suffer from field rotation, which means that the image of the object rotates in the eyepiece or camera as the telescope tracks it. This can be a problem for long-exposure photography, as it can cause star trails or distorted shapes.
• They do not use the equatorial coordinate system, which is the standard system for locating celestial objects. This can make it harder to find and identify objects in the sky.

Advantages and Disadvantages of Equatorial Mounts

Equatorial mounts have some advantages and disadvantages compared to altitude azimuth mounts. Here are some of them:

Advantages

• They are suitable for deep-sky observation and imaging, as they can smoothly track objects across the sky by moving only in one axis (RA). This eliminates the need for constant adjustment and field rotation.
• They use the equatorial coordinate system, which is the standard system for locating celestial objects. This can make it easier to find and identify objects in the sky, especially with computerized mounts that can automatically point at them.
• They can be used for astrophotography, as they can accurately follow the apparent motion of the stars and keep them in focus. They can also be equipped with guiding systems that can correct for any errors in tracking.

Disadvantages

• They are harder to set up and use, as they require polar alignment and balancing. Polar alignment is the process of aligning the RA axis with the Earth’s rotational axis, which can be done by using a polar scope, a smartphone app or a star alignment method. Balancing is the process of adjusting the weight distribution of the optical tube and the counterweight to prevent any strain on the mount’s motors or gears.
• They are more expensive than altitude azimuth mounts, as they have more parts and more precision. They also require more accessories, such as a polar scope, a wedge or a guiding system.
• They are heavier and bulkier than altitude azimuth mounts, especially German equatorial mounts, which have a long counterweight shaft. This can make them harder to store and transport.

Coordinate Systems for Altitude Azimuth Mounts and Equatorial Mounts

As mentioned before, altitude azimuth mounts and equatorial mounts use different coordinate systems to locate objects in the sky. These coordinate systems are based on different reference points and axes.

The coordinate system for altitude azimuth mounts is called AltAz or horizontal. It uses two coordinates: altitude (alt) and azimuth (az). Altitude is the angle of an object above the horizon, measured from 0° (horizon) to 90° (zenith). Azimuth is the angle of an object along the horizon, measured from 0° (north) to 360° (clockwise). For example, an object with an altitude of 45° and an azimuth of 180° would be halfway up in the southern sky.

The coordinate system for equatorial mounts is called equatorial or celestial. It uses two coordinates: right ascension (RA) and declination (DEC). Right ascension is the angle of an object along the celestial equator, measured from 0h (vernal equinox) to 24h (counterclockwise). Declination is the angle of an object above or below the celestial equator, measured from -90° (south celestial pole) to +90° (north celestial pole). For example, an object with a right ascension of 12h and a declination of +30° would be halfway up in the northern sky at noon.

Conclusion

Altitude azimuth mounts and equatorial mounts are two types of mounts that support telescopes and allow them to move and point at different objects in the sky. They have different designs, advantages, disadvantages, uses and coordinate systems.

Altitude azimuth mounts are simple and intuitive mounts that move in up/down (altitude) and left/right (azimuth) directions. They are easy to set up and use, cheaper than equatorial mounts, can handle heavier telescopes and are sufficient for planetary and lunar observation and imaging. However, they are not suitable for deep-sky observation and imaging, as they require constant adjustment in both axes, suffer from field rotation and do not use the equatorial coordinate system.

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