Skylabs NZ BlogStargazing, Astrophotography, Astronomy, Night Photography

Star Tracker Polar Alignment

in the Southern Hemisphere.

Jordi Blasco 2020-10-10

Star trackers are becoming quite popular for landscape astrophotography. That type of device is key for capturing stunning images with the Milky Way in the background. Unfortunately, setting up these special mounts can be challenging and frustrating for beginners.

Setting up a star tracker in the Northern Hemisphere is relatively easy, thanks to a bright star situated very close to the north celestial pole (Polaris). Unfortunately, there is no such a bright star in the Southern Hemisphere, indicating the south celestial pole. The stars of the Octans constellation represent the closest equivalent to Polaris, but they are in the human eyesight limit, even in a dark and clear sky.

In addition to that, there are situations where there is no visual access to Polaris or Octans asterism because of a mountain, building, trees, etc. Limiting the compositions and the scenarios that you want to capture just because of that seems entirely unreasonable.

In this article, I’m going to provide some tricks that will make this process easier and faster. This process does not require to have visual access to Polaris or Octans asterism. If you do, then you can get even more accurate alignment.

Requirements

You need just a few inexpensive accessories to achieve a painless polar alignment.

I previously used a rectified timber with a Vixen dovetail section and four silicone stickers to hold the smartphone. It worked quite well, but finally, I decided to design my own adapter. That particular design allows me to use an iPhone 6,7,8,10 with a protective case (and any other smartphone with similar dimensions), and it also supports QHY PoleMaster. It is compatible with any telescope mount and star tracker with a Vixen dovetail. I made two models, one for Southern Hemisphere and another for Northern Hemisphere (which has a standard slot for a finder).

The Southern Hemisphere version is currently available on Trademe (New Zealand). Check Skylabs NZ for other options.

Instructions

Set up the star tracker as usual and point to the celestial pole using the smartphone compass.

Star Tracker Levelling and Rough Alignment

  1. Level the tripod using the bubble level of the mount.
  2. Unscrew the azimuth screws to give more range during the alignment.
  3. Introduce the smartphone adapter to the star tracker dovetail bracket.
  4. Introduce the smartphone in the adapter.

Polar Scope Alignment App (iOS)

  1. Open the PS Align Pro App.
  2. Click on the three dots located on the bottom-right corner.
  3. Select the Daytime/No Polar scope alignment (Sun symbol).
  4. Move the mount with the AZ screws until the cross move just in the middle of the circle.

PolarAligner Pro App (Android)

  1. Open the PolarAligner Pro App.
  2. Click on the level button.
  3. Use the azimuth screws to tune the alignment with the pole.
  4. Click on the mount text in order to adjust the RA axis.

Further Accuracy

If you have followed the previous instructions, you should have quite reasonably good polar alignment. The described process works quite well for wide lenses (8mm to 50mm). If you have visual access to Polaris or Octans asterism, then those stars should be already visible through the polar scope.

The following steps will give you even better accuracy in your alignment.

  1. Take your smartphone from the adapter and open the “Polar Scope Alignment Pro” or “PolarAligner Pro App” again.
  2. Change the polar scope reticle with the one that you have. In my case, Skywatcher.
  3. Rotate the RA axis until the polar scope reticle aligns with the image you can see in your app.
  4. Move AZ screws and move Polaris or the Octans asterism into the right place.

Alternatively, if you have a QHY PoleMaster and the required adapter, you can follow the user guide instructions as usual.

Test Drift and Accuracy

To assess your polar alignment’s accuracy, you can point your telescope or lenses to a bright star from East. Take a long exposure (~5 minutes) and review it with your camera or computer if there is any evident drift. The longer is the focal length, and the longer is the exposure, the more challenging it will be for your mount to track the stars. In that case, you should consider guiding tools for correcting the tracking.

Other tutorials and strategies

What Telescope is Best for a Beginner

Tips

Jordi Blasco 2020-10-06

The best telescope is the one you will use the most

Your kids are showing a lot of interest in astronomy and stargazing. You think that a telescope could help grow their curiosity and ignite their passion for science and technology. Unfortunately, there are many choices in the market, which can make finding the right telescope very confusing.

  • How much should I spend?
  • What objects am I going to be able to see?
  • Will it be easy to use for my kids or even for myself?
  • How easy will be to find planets and deep-sky objects, like galaxies, nebulae, or globular clusters?
  • How much space will take at home when I am not using it?
  • Will it fit in my car when I go camping?

I’m going to provide some directions to identify the most suitable telescope for you and/or your kids. Before getting into many details, you should know that the best telescope is the one you will use the most.

Observing the Moon and the planets

If you want to see the Moon and the planets, a small refractor will reveal a nice image of the craters of the Moon and some details of Jupiter and Saturn. If you have more budget, you may want to consider a larger refractor or a compact catadioptric like a Maksutov-Cassegrain or a Schmidt-Cassegrain. Those telescopes are more expensive and can deliver a much higher magnification, which makes them ideal for solar system observation.

Be aware that the maximum magnification that you should consider is 2 times the diameter of the telescope aperture in mm. For example, a telescope with 90mm of the aperture will deliver a magnification of x180. Very cheap telescopes are usually advertised by really high magnification rather than by the aperture. Stay away from those telescopes!

Observing Deep Sky Objects

Planets and the Moon are very cool, but soon you and your kids will get bored of observing just a few objects. The next natural step will be to explore a list of Deep Sky Objects (DSO), which is almost endless. My recommendation for DSO (and also suitable for observing planets) is to consider a Newtonian telescope with at least 150mm of aperture, ideally 250mm. If you have more budget, you can consider a catadioptric like a 180mm Maksutov-Newtonian or a 250mm Schmidt-Cassegrain with a focal reducer.

Ideal telescope mounts for beginners

The ideal telescope mount for a beginner is alt-azimuth. That is because the eyepiece always stays in a comfortable position. With an equatorial mount, the eyepiece’s position can be challenging, especially for a Newtonian telescope. Equatorial mounts are mandatory for astrophotography and, from my point of view, are not the best option for beginners.

The most popular type of alt-azimuth mount is Dobson because it is cheap and easy to manage, even for a kid. Unfortunately, a Newtonian telescope with a Dobson mount (a.k.a. Dobsonian) can be quite heavy and bulky. The 250mm Dobson telescope I use in the Stargazing Labs can be used by ~9 years old kid but is around 30kg weight. If you go bigger than that, you probably need two people to move it; otherwise, you will need to spend some more time working out in the gym.

Computerized telescopes can help a lot to find objects, especially in highly polluted areas. Having this feature will increase the cost quite a bit.

Are you looking for something small?

If you are looking for something small that can fit in a backpack or a small car when you go camping, you should consider using binoculars with a tripod. I recommend 7x50 binoculars as a cheap option, or if you have more budget, consider bigger apertures like 20x80 or 25X100.

Summary

Additional cheap accessories to be considered

Collimation tools

The mirrors of the telescope need to be well aligned to deliver a high-quality image. If you end up with a Newton telescope, you should consider buying a Cheshire eyepiece. Single beam laser collimators are relatively affordable and easy to use. Unfortunately, they can not help correct the off-axis position of the secondary mirror or ensure the collimation of both mirrors’ surfaces. While the laser collimator helps speed up the process, to ensure the perfect collimation between the two mirrors, a Cheshire is always required. If your main mirror has no central spot, you should consider getting a mirror spotting template and center spots stickers.

The Maksutov-Cassegrain and Schmidt-Cassegrain telescopes can be collimated with a bright star or using an inexpensive tri-Bahtinov mask.

Light pollution filters

These filters try to reduce as much as possible the artificial light coming from the city. While those filters are transparent for a wide range of the spectrum, it blocks certain particular regions of well known artificial light bulbs. Knowing the dominant light pollution in your city will help you choose the right filter to save time and money.

I highly recommend the Ultra-High Contrast filter, which allows the transmission of nearly 100% of the radiation from both O-III and the H beta lines. All annoying, scattered light from other wavelength sources, including local artificial light pollution, is filtered out. With this strong blocking of the sky, a great detail becomes visible for gas nebulae and planetary nebulae.

UHC-E variant increases the contrast of emission nebulae and also comets. It’s recommended for observation of emission nebulae and comets with small telescopes under light-polluted skies.

Neutral density filter

Most probably, your new telescope will also come with a not very useful Moon filter. I strongly recommend getting a neutral density filter (0.8, 0.9). That reduces the bright glare of the Moon and reveals a highly lunar detail and surface features.

Red dot or projection finder

Until you are very familiar with the night sky, you can lose many hours trying to find a particular object. Nothing is more frustrating than a star cluster, a nebula, or a galaxy that you want to look at but simply cannot find. The red dot and projector finders can help to reduce this frustration.

Still not sure?

I hope this information has been useful and it helps you decide what telescope is best for you.

Stargazing Labs

If you are still unsure about what telescope suits you best, consider attending a stargazing session in your local astronomical society or, if you are living in Auckland, consider joining one of the Stargazing Lab organized by Skylabs in Maraetai Beach.

Telescope Labs

If you already have a telescope and you would like to learn how to use it, Skylabs can help you. In the Telescope Labs, you will learn how to assemble and balance your telescope properly, align the finderscope, collimate the mirrors, and choose the appropriate eyepieces. Skylabs can also help you learn how to find objects in the sky with your telescope.