Star Tracker Tutorial

November 14, 2017  •  10 Comments

Tired of grainy Milky Way photos?  Don't want to spend $2,000 on a new wide angle lens?  A star tracker is the easiest, and most cost effective, way to capture higher quality nightscapes!  These devices move the camera at the same speed as the stars, allowing you to take much longer photos without any star trails.  The key to this process is a proper polar alignment.  The star tracker must be pointed directly at Polaris, the North Star.  (Or, if you are in the southern hemisphere, Sigma Octantis.)  This can be surprisingly difficult!  This tutorial will cover everything you need to know about using a star tracker, from choosing the correct model, to setting it up, and even post processing!

Before we get into the tutorial, I thought I'd show some images taken with the my iOptron Skytracker Pro

Andromeda GalaxyAndromeda GalaxyUsing a Tamron 70-200mm and iOptron Skytracker Pro I was able to capture the Andromeda Galaxy Orion NebulaOrion NebulaUsing a Tamron 70-200mm lens and an iOptron Skytracker Pro I was able to capture the Orion Nebula Rho OphiuchiRho OphiuchiThe Rho Ophiuchi cloud complex Temple of the SunTemple of the SunThe Milky Way over the Temple of the Sun in Capitol Reef National Park Kenosha PassKenosha PassThe Milky Way rises over Colorado, as seen from Kenosha Pass. Trillium Lake - MidnightTrillium Lake - MidnightThe Milky Way shines brightly over Trillium Lake. Mount Hood can be seen in the distance The Galactic CoreThe Galactic CoreA detailed look at the Milky Way galaxy, the Lagoon Nebula and Trifid Nebula can be seen as well

 

Choosing a Star Tracker


A quick Google search will yield at least 3 potential options for a good star tracker.  Some of the most popular star trackers include the iOptron SkyTracker Pro, the iOptron SkyGuider Pro, the Sky-Watcher Star Adventurer, and the Vixen Polarie.  There are even more mounts out there, but those are more for telescope users.  I'm focusing on photographers who are just getting into astrophotography.  Let's try to make the decision a bit easier.  There are a number of factors to consider before you purchase your star tracker.

I recently created an overview of the iOptron SkyTracker Pro, which I would recommend watching first.  This will give you an overview of how most star trackers actually work.

 

Weight Limit

First, you need to determine the weight of your gear.  This includes the camera body, any L-Brackets or tripod plates attached, your lens(es) and the ballhead you will be using.  One of the main differences between the different star trackers is how much weight they can handle.  If you only have an entry-level DSLR and a kit lens, nothing special is required.  However, if you have a bulky full-frame DSLR with a large wide-angle or telephoto lens attached, you will probably want to consider a star tracker that can handle an increased payload.  If you try to put too much weight on your star tracker, it will fail to track.

I personally own the iOptron SkyTracker Pro, which has a 6.6 payload capacity.  However, in the small print, iOptron specifies "for camera rigs up to 2.6 pounds, or with an optional counterweight kit - for rigs from 2.6 to 6.6 pounds, including the lens."  2.6 lbs is nothing!  My D750 alone weighs 1.7 lbs!  iOptron does sell an optional counterweight, which will allow the star tracker to operate with a heavier payload (in this case, up to 6.6 lbs).  I recently purchased this counterweight, and it's surprisingly heavy.  You will not want to bring this on a hiking or backpacking trip as it weighs at least 5 lbs!  If you know you've got some heavier gear, you might be better off purchasing another star tracker that has a higher payload by default. 

Having used the SkyTracker Pro's counterweight kit for a big lens, I can't really recommend it.  If you plan to use a 70-200mm or larger lens, you should probably opt for a different tracker.  The SkyTracker Pro simply isn't designed to handle such big lenses, even with the counterweight.  I was able to make it work, but I felt that it was pushing the system to the limit.  

The SkyGuider Pro does come with a counterweight kit included.  If you use that counterweight system, you can push the SkyGuider Pro up to 11lbs.  Frankly, I probably should have gone with that system since my setup is quite heavy.  As mentioned above, the SkyTracker Pro does not come a counterweight kit, it's an optional $80 accessory that will increase the max payload to 6.6 lbs.

To give you some first hand feedback, let's take a look at my gear weight first:  

  • Nikon D750: 1.7 lbs
  • Kirk L Bracket: 0.27 lbs
  • Acratech GP Ballhead: 1 lb
  • Tokina 100mm: 1.2 lbs
  • Nikon 14-24mm: 2.18 lbs
  • Tamron 70-200mm G2: 3.28 lbs
  • Tamron 150-600mm: 4.3 lbs

So, with just my D750 (with L bracket attached) and my ballhead, I'm already at the 2.6 lb limit of the Skytracker!  ...I really should have gone with the SkyGuider Pro.  With that said, I've managed to shoot 60 second exposures at 100mm without tracking errors.  That would put me nearly 2 lbs over the weight limit, while still getting good results.  With the 14mm lens, I was able to successfully track up to 4 minutes without any problems.  However, it's possible that I may be damaging some interior components, pushing the system this hard.

The only time I've actually had trouble tracking was with the Tamron 70-200mm G2 attached.  This not only put my camera over the weight limit, it changed the center of gravity too much.  With that said, I was still able to successfully track with the 70-200mm on the SkyTracker Pro, but it wasn't easy!  Keep in mind, the more zoom you have, the more precise you need the Star Tracker to be!  At 14mm, the FOV is so wide that a slight misalignment likely won't be visible.  At 200mm+ however, you need to be spot on!

 

Counterweight Kit

Once I realized just how much my camera gear actually weighed, I decided to buy the optional counterweight kit for the SkyTracker Pro.  It consists of 3 pieces: a screw with a rotating lever attached, the rod that holds the counterweight, and a dovetail bar that holds everything together.  The initial setup is not hard, it took me about 5 minutes.  You can read iOptron's official instructions here or watch my video at the top of this post for complete installation instructions!

As an amateur astrophotographer, balancing the counterweight was initially very confusing.  There are no instructions provided from iOptron on this process, and finding information online is difficult.  If you're also new to this, you'll probably be left scratching your head.  This video helped explain how to balance a counterweight, although it is geared towards big telescopes.  I'd still recommend watching it though.

As mentioned above, the SkyTracker Pro counterweight kit isn't great.  If you plan to use a 70-200mm or larger lens, I would spend the extra money and get either the SkyGuider Pro or another tracker that can handle a heavier payload.  The SkyTracker Pro simply wasn't designed for big telephoto lenses. 

 

Ease of Use

Another thing to consider when purchasing a star tracker is how easy it is to setup.  There are 2 critical factors to a good alignment.  The star tracker must be level, and it must be pointed directly at the North Star.  The iOptron SkyTracker Pro and SkyGuider Pro have a few features to make this relatively easy.  First, they come with their own base that can be attached to directly to your tripod.  The base includes a bubble level and latitude adjustment.  Second, they both include a polar scope.  You can look through the scope to help find the North Star and ensure a very accurate alignment.

To get your Star Tracker pointed directly at the North Star, you'll need to do 2 things.  First, determine your latitude.  I recommend the Photographer's Ephemeris App.  It will show your current latitude in the upper right of the app.  Then, you can dial that in on your SkyTracker Pro base easily.  Again, watch my YouTube tutorial video to see that.  Once the latitude is correct, you'll need to move the tripod so the Star Tracker is facing North.  From there, use the Polar Scope or Quick Sight Hole to find the North Star.

Alternatively, you can attach the SkyTracker Pro or Vixen Polarie directly to a ballhead.  This gives you the freedom to move the star tracker where ever you need to.  However, that method requires 2 ballhead, since you will need another ballhead for the camera.  I like using the SkyTracker Pro's included base.  I find it makes accurate polar alignments relatively easy.

You can use the thumbscrews at the base of the SkyTrackermount to move the star tracker left or right.  This will help with precise alignments.  You can also use the <> button on the back of the SkyTracker Pro to rotate the camera mount either clockwise or counter-clockwise.  Using the <> button allows you to reframe your galaxy or nebula without having to move the ballhead.  This is explained better in the video embedded near the top of this blog post.

The Vixen Polarie does not come with its own base.  Therefore, you will need 2 ballheads to make it work.  One ballhead would hold the Polarie on the tripod, the other would be attached to the Polarie's rotating mount and used to hold your DSLR.  This could make alignment more difficult.  You can no longer just dial in your latitude and face the tripod to the North Star, like the iOptron models.  You will need to carefully move the ballhead around and do a lot of tweaking.  The Polarie does not have a polar scope either, only a quick-sight hole.  This will likely make alignment harder as well.

 

Battery

This one comes down to personal preference.  The Vixen Polarie and Sky-Watcher Star Adventurer both use AA batteries, while the iOptron Skytracker and SkyGuider have a rechargeable battery.  In my experience with the SkyTracker Pro, I don't mind the rechargeable battery.  I know I can always charge it while I'm driving to my photography location!  However, if I end up killing the battery overnight, I'm out of luck.  I'll need to wait for it to charge.  If I was using something like the Vixen Polarie though, which takes AA's, I would never have to worry about a low battery; I could simply pop in some fresh AA's and keep shooting.  Consider which option would work better for you.

 

Size

If you plan to take your star tracker on backpacking or hiking trips, you're probably gonna want a small, light weight model.  This limits you to either the iOptron SkyTracker Pro, Vixen Polarie, or SkyGuider Pro.  They will all fit in the palm of your hand and don't weigh very much at all.  From what I've seen, pretty much every other star tracker on the market is too heavy / bulky to take on an overnight backpacking trip.  This was one of the major reasons I chose the Skytracker Pro.  However, over the course of my 2017 roadtrip, I almost always found myself using it near the car.  I really didn't do much backpacking, so the lightweight benefits were largely useless and I often found myself wishing I had a star tracker with a heavier payload capacity.  As mentioned earlier, the optional counterweight kits are quite heavy and you will probably want to leave those behind on hiking / backpacking trips.

 

Alignment

This is arguably the most important factor when choosing a star tracker.  If it's a pain to align, you're never going to get the sharp stars you want!  Remember, getting the star tracker level and pointed at the North Star is critical for a good alignment.  When I was traveling on the road, I didn't realize that the iOptron Polar Scope could be focused better, so the stars were always blurry when I looked through the polar scope.  Therefore, I started to simply eye-ball it, using the scope like a gunsight.  This usually worked well enough for the 14mm photos, but I needed to be much more precise when using the 70-200mm or 100mm lens.

If you still aren't sure how to find the North Star, I recently made a quick image guide.  You will need to find the Big Dipper first.  Then draw a line out from the upper right star in the Big Dipper, it will point directly to the North Star.  Click here to see the image guide.  All of the stars in the sky will appear to revolve around the North Star.

The problem with the SkyGuider Pro is that you need to completely remove your ballhead and camera setup to look through the provided scope.  You can see exactly what I mean in this Youtube video SkyGuider Pro.  This makes the SkyTracker Pro a more attractive option, since you can still look through the scope while your gear is attached.

The Vixen Polarie only has a small hole to help with alignment, it does not come with a polar scope.  However, you can buy one for an additional fee.  It will slot into the quicksight hole.  The SkyTracker Pro also has a quick-sight hole, similar to the Polarie.  In my experience, it was very hard to use the quick-sight hole to align.  I wouldn't want to be stuck with this method.  Using the polar scope, while still not easy, was better.  

Finally, for extremely precise alignments you will need an app.  This app will show exactly where to position the North Star (or Sigma Octantis) in your polar scope reticle.  For Android users, Polar Finder App will do the job.  Make sure to change the reticle to iOptron in the wrench menu.  Those of you on iPhone can download the official iOptron Polar Scope App.  In either app, you will see a green dot somewhere in the reticle once it loads in your location data.  You will need to position the North Star in the same spot on your polar scope reticle for precises alignments.  Realistically though, this is only necessary for very long exposures (3 minutes+) at 100mm+.  If you are using a wide angle lens, you really don't really need to worry about being that accurate.  Again, check out the video above for more information on using the app.

 

 

Aligning the Star Tracker


Now that you've selected your star tracker, it's time to align it properly.  Since I only have access to the iOptron SkyTracker Pro, I will be using this for demonstration.  Regardless of which tracker you choose, the process will be very similar.  Again, I recommend watching my YouTube tutorial that shows you how to do these steps on the Skytracker Pro.

I am currently working on another tutorial that shows you exactly how to do these steps in the field.  I will update the blog post with that video soon.

  1. Find North Star  
  2. Setup tripod and attach your star tracker
  3. Level the tripod and make sure the star tracker is facing North
  4. If using the iOptron models, adjust the base for your current latitude  (Use TPE to determine latitude)
  5. Look through Polar Scope hole / Quicksight hole, make sure North Star is visible
  6. Attach Polar Scope
  7. Open App and verify proper North Star location on reticule
  8. Use the thumbscrews to rotate the star tracker precisely 
  9. May also need to re-adjust laltitude
  10. Make sure Polaris is in the same spot as in App

Alright!  At this point, the star tracker should be aligned precisely.  Remember to tighten all the screws back down.  I give the star tracker a gentle wiggle to ensure everything is tight.  At this point, be careful not to move the tripod or star tracker.  Depending on your tripod, sometimes the star tracker will rotate around at the base, where it is attached.  If this accidently happens, you'll need to re-align. 

Now we're ready to finish the star tracker setup and begin taking photos!  

  1. Attach your camera gear to the star tracker
  2. Double check ballhead is secure!
  3. Turn on Live View, zoom in, and focus lens to stars
  4. Take a test shot to check composition and focus
  5. Look through the Polar Scope or quicksight hole again, make sure the North Star is still there
  6. Turn on the Star Tracker
  7. Take a long test photo to verify stars are sharp and tracker is properly aligned
  8. If stars are blurry, you need to troubleshoot

There are usually 3 reasons why you are still seeing star trails.  First, make sure the star tracker is turned on.  Second, make sure you have the North Star visible and aligned properly in the polar scope.  Third, check your counterweight.  If you are not using a counterweight, it's possible that your camera gear is too heavy for the mount.  If you do have a counterweight, it's probably unbalanced.  Try moving the counterweight higher up for lighter lenses, and lower down for bigger lenses.  You may even need to remove the counterweight entirely and just leave the counterweight rail attached.

 

  1. Take another test shot
  2. Stars are now sharp over long exposure
  3. Set camera to Manual Mode, Shutter Speed to Bulb.  Enable Wireless Remote or attach wired remote
  4. Get out your smartphone so you can time the exposures.  Alternatively, set your external intervalometer settings
  5. Turn on LENR if taking 1 minute+ photos (only necessary on warm nights (I.E. ~40F+))
  6. Now we're ready to take a long exposure!! 
  7. Depending on focal length and alignment accuracy, take your photo
  8. Here are some rough guidelines:
  9. 1 minute for 100mm, 2 min for 35mm, 4 minutes for 14mm
  10. Use smartphone to time your exposure
  11. Check to see if stars show motion.  If so, use shorter time.  If stars have coma, consider stopping down the Aperture.  Double check the Star Tracker is actually turned on.
  12. After taking your tracked photo, turn off the Star tracker.  Now take another exposure, of equal length.  You can blend the foreground and stars later.


Other tips:

  • Turn off tracker when not in use to conserve battery
  • Don't move tripod!  Otherwise you'll have to realign.
  • Take multiple photos.  Can blend them in post to reduce noise and increase detail.  No more than 20 needed.
  • I recommend 4 minute exposure at ISO 800 for foreground photo on a moonless night.  Should capture plenty of light.  Make sure Star Tracker is turned Off
  • Polar alignment precision is unnecessary when shooting wide angle photos (~14mm - 35mm), as long as you're close you should be fine!
  • For 50mm+ photos, make sure to do precise alignment

 

 

Post Processing


Hopefully you remembered to take a long exposure for the stars, as well as a long exposure for the foreground!  I recommend ISO 800, f/2.8, and a 4 minute Shutter Speed to capture enough light for the foreground.  This will make a huge difference in the amount of light gathered compared to an ISO 6400, 30 second photo!  Trust me, it's worth it!

The problem we now face is that, while our stars are sharp, the foreground is blurry.  You will need to blend two exposures, foreground and stars, to have a complete image now.

Watch the YouTube video below for a full walk-through on blending 2 exposures together.

 

If you are doing deep space astrophotography, like nebulae or galaxies, there's another process we can try.  It's called Median Stacking.  This is where we take multiple photos and stack them to reduce noise.  In each photo there is random noise / grain which obstructs fine detail.  By stacking multiple photos, Photoshop is able to find the static detail (galaxy, nebula, stars) and effectively remove the random grain in the photo.  This process works very well when using a star tracker!  I recommend taking at least 20 exposures at night for this to work well. 

Alternatively, you can do a much more advanced procedure using Deep Sky Stacker.  If you are a photographer first, and astronomer second though, like me, stick with the Photoshop workflow for now.  You can watch the full tutorial below.


Comments

Peter Zelinka
Great question! Take a look at this image first:

https://cdn3.volusion.com/wlcsk.dppva/v/vspfiles/photos/3550-3.jpg?1490016461

As you can see, the SkyGuider Pro is facing in one direction, while the camera is facing the opposite direction. The key component here is a ballhead. Once a ballhead is attached to the rotating mount on the star tracker, you can point the camera whichever direction you want.

Let me know if you have any more questions about the star trackers, I know they can be confusing at first!
Linda Urban(non-registered)
Peter,
When photographing the Milky Way with the iOptron, how do you point it towards Polaris and the camera toward the Milky Way?
Peter Zelinka
Hey Rodrigo,

I used the Tamron 70-200mm G2 lens for the Orion and Andromeda photos. I did not use the optional counterweight for those photos. Instead, I simply attached my camera directly to the ballhead (instead of using the lens' tripod collar mount, like you would normally do).

This seemed to offset the weight of the lens better and the tracker worked. When I tried tracking with the lens collar mounted on the ballhead, it would not work properly.

The optional counterweight might not be a bad idea if you plan to use a big / heavy lens!
Rodrigo Rosa(non-registered)
Hello Peter! Great images! Congratulations! For Andromeda and Orion Nebula what lens do you use? Is it not necessary counterweight? Thank you!
Peter Zelinka
Hey Natasha,

For my deep-sky photos, I normally shot for around 20 seconds, and stacked 20 exposures together. When shooting at 100mm+, I set the camera to ISO 1600 and either f/2.8 or f/4, depending on the lens' performance wide-open.

Honestly though, it just comes down to your alignment. If you are perfectly aligned, you will be able to shoot much longer exposures without motion blur.

Another thing to consider is the weight of your lens. When I was using the 70-200, I couldn't get the star tracker to work properly, since the lens weighed too much for the mount. However, once I mounted the camera body itself (not the lens' tripod collar) to the star tracker, it was able to track properly. I think it had to do with the new weight distribution.
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