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What is a star tracker?

A star tracker is a type of mount that can track the motion of the stars, allowing for long exposure astrophotography. Star trackers have become immensely popular in the last few years, as you can easily attach a DSLR or Mirrorless camera and lens and take excellent astrophotographs. Star trackers are a perfect entry into the hobby of astrophotography as you don't need a telescope to begin.

Why are star trackers great for astrophotography?

When you take astrophotographs with just a camera on a tripod, you are limited to short exposures of 30 seconds or less before star trailing occurs due to the Earth's rotation. This appears as the stars streaking as lines in your image. The longer the focal length of your lens, the shorter your exposures must be to avoid star trails. By using a star tracker, you can cancel out the motion of the Earth's rotation, which lets you expose for several minutes at a time. This greatly increases detail, overall brightness, and sharpness of your astrophotography images. Some users can see a 10x increase in exposure time when using a star tracker, which allows for endless possibilities of objects to photograph. This even includes long focal lengths of up to 200mm or more, meaning you can even use some lightweight telescopes like the William Optics RedCat 51 with them. With just a tripod, you will be limited to capturing just the Milky Way or constellations. With a star tracker, especially paired with a telephoto lens, you can capture detailed views of the Milky Way, and wide field views of deep sky objects such as galaxies, nebulae, and more.

Tripod vs Star Tracker

Image courtesy of AstroBackyard

How does a star tracker work?

Star trackers work by polar aligning to the celestial pole, which in turn allows them to track the night sky and let you take long exposures. Star trackers can be thought of as miniature, simplified versions of equatorial mounts, which are what most deep sky astrophotographers use to mount a telescope and capture incredible photographs of space.

Celestial Pole

What is polar alignment?

Polar alignment is the process of aligning a star tracker or equatorial mount's axis with the north or south celestial pole, the same axis Earth spins on. As a result, this allows the star tracker to cancel out the Earth's rotation. In essence, this means the stars appear to stay still from your camera's point of view, allowing for much longer exposures and therefore better astrophotography images. Polar alignment is a critical step to using a star tracker or any equatorial mount. The more accurate your polar alignment is, the longer you can expose for before stars begin to trail. Some higher-end star trackers come with a proper polar alignment scope that make this step much easier.

What is payload capacity on a star tracker?

Payload capacity is a specified maximum weight that the star tracker or mount can carry. The payload includes anything riding on top of the star tracker or mount, including your camera, lens/telescope, and any other accessories like a guide scope. When using any mount for astrophotography, the rule of thumb is that your payload should be approximately half of the total payload capacity for the mount. This ensures accurate tracking without star trails, even at long focal lengths. For example, if the payload capacity of the star tracker is 11 lbs and you want to use it for astrophotography, the total weight of your camera and lens/telescope should be 5.5 lbs or less for best results. Note that this is a rule of thumb. Depending on other factors like balance and polar alignment, it can sometimes be pushed slightly. Almost all star trackers are designed to be able to work well with a DSLR or Mirrorless camera and a lightweight camera lens.









FAQs

Still have questions? We have answers.

What's the difference between a star tracker and an equatorial mount?

Star trackers are very similar to equatorial mounts except they are smaller and more portable, but there are a couple of key differences worth noting. For one, star trackers only track in one axis (right ascension), whereas equatorial mounts track in both axes (right ascension and declination), which makes EQ mounts significantly more accurate at tracking. For wide angle lenses, though, this level of accuracy is overkill, which is why star trackers are more than adequate for a DSLR or Mirrorless camera and a lens. Second, most star trackers use a counterweight that's not as heavy as the actual payload, if they use a counterweight at all. In theory, this can lead to balance issues, but is rarely an issue unless you're using a heavy lens or telescope. In that case, you might be best off with an equatorial mount. In short, star trackers are perfect for a lightweight travel tracking rig and are best paired with a DSLR or Mirrorless camera and lens for wide field astrophotography. Equatorial mounts are much heavier and less portable, but can carry a much heavier payload like a telescope and other imaging accessories.

Which star tracker should I buy?

There are a number of different star trackers out there, and the choices can be overwhelming to a beginner! Currently, the Sky-Watcher Star Adventurer Pro and the iOptron SkyGuider Pro are both excellent options for most skill levels and budgets and are probably the popular options we sell. They are both very similar with payload capacities of 11 lbs (5.5 for imaging), and use electronically-driven motors to track the Earth's rotation.

If both of those are out of your budget, there are less expensive options, such as the purely mechanical Omegon LX2. This particular model has a much lighter payload capacity, so it can only hold a DSLR or Mirrorless camera and a camera lens — the lighter, the better. But it's also the most portable star tracker option as well.

Do star trackers come with a tripod?

No, star trackers usually come with only the mount head itself, and maybe a counterweight system if you're buying the Pro version. The Sky-Watcher Star Adventurer tripod can work with most star trackers if you don't already own one. If you want a rock-solid tripod that can hold a heavy load, the Radian Carbon Fiber tripod is an excellent choice.

Do I need a ball head for my star tracker?

Most star trackers do not come with a ball head, which allow you to easily orient the camera freely to point it at various targets in the sky instead of only where the star tracker is pointing. Many photography tripods come with a ball head that can be used on star trackers, but If you need one separately, the iOptron Ball Head is a great option.