German Equatorial Mounts - Go To
The image at right depicts a German equatorial mount with a refractor telescope. The telescope and counterweight rotate about the right-ascension axis, which must be oriented parallel to the Earth's axis of rotation. The counterweight is used to balance the weight of the telescope and other instruments or accessories such that the telescope can track and slew with minimal power consumption and strain on the motor. The telescope also rotates about a second axis, known as the declination axis, which is perpendicular to the right ascension axis. Balance on this axis is achieved by moving the telescope within its mounting rings, or by moving the entire telescope and ring assembly in the mount saddle along the mating dovetail bar.
Alignment of the right-ascension axis with the Earth's axis of rotation is more commonly referred to as polar alignment. Residents of the norther hemisphere are fortunate to have a reasonably bright star near the celestial pole. The north star Polaris is located about two thirds of one degree from the true celestial pole. Most but not all German equatorial mounts are equipped with a sight tube through the middle of the right ascension axis. Rough polar alignment is achieved by sighting Polaris through this tube. A rough polar alignment is generally good enough for visual observing, but a more precise polar alignment is required for astrophotography. This can be achieved using a polar alignment scope, software assisted methods embedded in the on-board computer systems of some go-to German equatorial mounts, or a combination of these techniques.
German Equatorial Mounts - Go To
German Equatorial Mounts
German equatorial mounts, also known as GEMsprovide a stable foundation for both astrophotography and celestial observation.
German equatorial mounts are defined by their movement, which pivots around an axis aligned with the earth’s rotation axis. While this type of movement is less intuitive and slightly more awkward for traditional viewing, it’s essential for astrophotography for its ability to track an object without field rotation. German equatorial mounts are easily identified by their counterweight, which is used to balance the telescope across the primary axis of the mount, or polar axis, resulting in greater stability and weight capacity.
Movement of German Equatorial Mounts
German equatorial mounts make use of two axes: right ascension and declination. The right ascension or polar axis is the primary axis of the mount and is aligned toward the north celestial pole near Polaris, the north star. Since Polaris is a relatively fixed point in space located only two-thirds a degree away from the true celestial pole, rotating around an axis aligned to Polaris allows the visual observer to follow objects more easily. Astrophotographers will align to the true celestial pole for the best possible tracking.
The declination axis, however, is the axis the counterweight shaft. Movement on the declination axis allows for adjustments perpendicular to the polar axis. Movement around the polar axis allows for east and west movement in celestrial coordinates, while movement around the declination axis goes north and south.
German Equatorial Mount Features
A few more common features to consider include:
- PEC: The PEC system automatically corrects these errors in the computerized equatorial mount as the mount tracks an object across the night sky, making for a smoother and more accurate tracking of the target. This is particularly important for long exposure Astrophotography.
- Polar Alignment: Alignment with the celestial pole is essential for proper use of a German equatorial mount, which is why most are equipped with a sight tube through the middle of the declination axis or an alignment software system. The best astrophotography mounts may use a combination of both.
The motions necessary to locate an object using a German equatorial mount can be baffling to beginners. For that reason, we make it a rule to never recommend such mounts for young children. Our fellow amateur astronomer Jeff DeTray has published an online EQ mount tutorial that is complete with animated examples of how these mounts move. This recommended reading for first time German equatorial mount buyers, even if you are considering a go-to mount.
If you’re considering purchasing a German equatorial mount of your own or are wondering which is the best telescope mount for astrophotography, Skies Unlimited can help. We’re committed to providing you with high quality German equatorial mounts, along with the advice you need to use them correctly.
Founded in 2004 by real amateur astronomers, Skies Unlimited was started with the goal of making amateur astronomy easier and more accessible for the masses with practical knowledge and quality products. That’s why we employ a team of amateur astronomers with years of personal and professional knowledge in the field — any one of our team members can give you advice backed by both personal and professional experience. Call Skies Unlimited today or visit our Pottstown, Pa., location to get started on your next purchase.