What is an Auto-Guider?

Last Updated: April 26, 2020

An auto-guider is a small camera that sends commands to your star tracker, drastically increasing the tracking accuracy!

In order to use the auto-guider, you'll also need a guide scope.  This guide scope is just a small lens that allows the auto-guider camera to see the stars.  Once you have an auto-guider and guide scope, a USB cable will connect the auto-guider to your laptop.  You'll also use an ST4 cable to connect the auto-guider to your star tracker. 

In order to actual do the 'auto-guiding', you'll need a free application - PHD2.  This program has two main functions.  First, it will find a guide star and lock on.  After a guide star has been selected, PHD2 can send commands to your star tracker, which should keep the guide star centered in the crosshairs.  Now that PHD2 is sending commands to your star tracker, it should perform much better!  If you are shooting at 200mm+, you'll likely notice a massive change in tracking accuracy! 

This photo shows my old hotshoe mount, which I no longer use due to stability problems.  I now use an arca-swiss clamp to connect the guide scope directly to my D750's L-Bracket 

Choosing an Auto-Guider

You have a lot of options when choosing an auto-guider, including the ZWO ASI 120MM S, Lodestar X2, and the QHY5L - II.  Depending on which auto-guider you get, you may also need to purchase a guide scope.  This is a tiny lens that allows the auto-guider to see the stars.  

Once you have an auto-guider and guide scope, you need to mount everything to your camera / star tracker.  If you have the Star Adventurer, I recommend checking out this video for installation options.  If you have an L-Bracket attached to your DSLR, you have another way to mount your auto-guider and guide scope.  Simply buy a quick release clamp like this (there's a bunch of other similar options that will work too).  You can screw this into the base of your guide scope, then clamp the whole thing to the side of your L-Bracket.  This will give you a much sturdier connection, with no wobble!  Plus, it will lower the center of gravity.  The only caution here is that some of your camera ports may be blocked.  Thankfully, I'm still able to plug in my external remote when the clamp is attached.  I want to thank 2 of my students - Mahn and Phil, who let me know about this wonderful idea!  

Personally, I bought the ZWO ASI 120MM Mini auto-guider with the ZWO 30mm f/4 Guide Scope.  This combo works great, and is fairly cheap!  However, you may have compatibility issues with the ASI 120MM Mini camera, due to the USB 2.0 interface.  Therefore, you may want to consider the ZWO ASI 120MM S version instead.  It has USB 3.0 and is reportedly much more stable, especially with newer laptops.  

There are also similar cameras to the ones linked above, but they might have the letters 'MC' in their name.  For example, the ASI 120MC-S.  This camera has a color sensor, as indicated by the "MC" marking.  Color cameras aren't as sensitive to light, and I'd recommend buying a monochrome camera - like the ASI 120MM Mini instead.

Here you can see my new guide scope mount.  I use an arca-swiss clamp to connect the guide scope directly to the L-Bracket on my D750.  This provides a very stable, secure connection

The Guiding Process

Before you begin guiding, you'll need to download the appropriate drivers for your auto-guider.  First, you need the Native Drivers for your auto-guider camera.  Here's a link to ZWO's software page, and here's a link to QHY's page.  It's always best to search for your specific camera model though, and be sure to get the correct Native (System) Drivers.  This will depend on which brand you bought, but it's a pretty simple process to get everything running.  After your drivers are installed, you can now plug the auto-guider into your laptop.

Believe it or not, the actual auto-guiding process is very simple.  Once your auto-guider is connected to the laptop via USB, and to the star tracker via ST4, you are ready to go!  You'll need PHD2 installed on your laptop for the guiding.  PHD2 is a great, free application that makes the guiding process very simple.  Once PHD2 is running, there's really only 5 steps to follow.

1. Connect your equipment
   1. Click the USB icon at the bottom
   2. Then click the "Connect" buttons for your equipment
2. Begin 'Looping' Exposures
   • Adjust your 'Exposure' and 'Gamma' as needed
   • If you don't see any stars, it's possible your guide-scope needs focused
3. Click on any star to select it
   1. Don't always click the brightest star, it won't help the tracking
   2. If you're not sure, use Auto-Select (Alt S) and PHD2 will automatically pick a good star for you
4. Click the Begin Guiding button
   1. PHD2 will now calibrate on the star
   2. You should see yellow dotted lines
   3. The calibration should take ~2 minutes to complete
   4. Once it finishes, the yellow lines will turn green and the guiding will begin!

That's all there is to it!  Once the initial calibration phase has finished, you'll notice the yellow lines turn green.  At this point, PHD2 is sending guiding commands to your star tracker.  It should help to correct any errors with your tracker, and allow you to shoot much longer exposures at 100mm+.

You can certainly get more advanced with PHD2, by adjusting various algorithms, but it's really not necessary.  It is called Push Here Dummy for a reason!  After you use PHD2 two or three times, you should be more than comfortable with the interface.  The image below shows the main PHD2 screen.  The graph is the most important part.  It shows how well your star tracker is performing.  Ideally, the blue 'RA' line would be nearly flat, along the 0 line.  However, even if the RA line oscillates between +6" and -6", you should still get good results!  There's a lot more complexity to this, which I cover in my Auto-Guider Course.

ZWO ASIAir

The ZWO ASIAir allows you to guide your star tracker from your smartphone, no laptop required!  I purchased my original ASIAir in September, and found that it makes my night a lot easier!  I no longer have to bring my old laptop out into the field, along with my big Jackery battery.  The ASIAir itself is not much bigger than a cell phone, and can be powered from a small battery charger.  I use this RAVPower battery, and it can easily power the ASIAir for multiple nights.  This makes it the perfect companion of a SkyGuider Pro or Star Adventurer.  The most important aspect of the ASIAir is that you can now do everything from your smartphone!

Unfortunately, ZWO has discontinued the original version of the ASIAir.  I really liked this model because it could be powered from a USB cable and small battery.  They now make the ASIAir Pro, which has some noticeable improvements and drawbacks.

The new ZWO ASIAir Pro is more designed for astrophotographers with dedicated astro cameras and go-to mounts.  The ASIAir Pro has 4 DC power ports, which can be used to power a variety of astro accessories.  The ASIAir Pro also has a more robust design, which is a welcome improvement over the original.  My only problem with the ASIAir Pro is that it requires a 12V power connection now, which means I need to lug around my big Jackery battery whenever I use it.  

The ASIAir app is pretty straightforward, although it did take me a few hours to get used to the interface.  Once you know how to use the ASIAir, you'll be able to quickly do a precise polar alignment and start guiding.  I recommend watching my tutorial below for more information.

If you're thinking about getting an auto-guider, I'd highly recommend the ZWO ASIAir as well!  

How Well Does it Work?

I was honestly very surprised how well the auto-guiding worked!  In the past, I was usually limited to ~30 second exposures when shooting with my Tamron 150-600mm lens.  Now that I am using an auto-guider, I can easily shoot 4+ minute exposures at 600mm!!  This is a huge boost in light gathering capabilities!  The extra light should allow you to capture more detail and color in your nebulae, with noticeably less grain!  Since you are taking much longer exposures, you will also have less images to deal with.  Instead of stacking 100+ images, you probably only need 10 - 40 images, in most cases.  That means more harddrive space, and less processing power required.

The comparison below shows two 5 minute exposures, one with the auto-guider connected, and one without an auto-guider.  As you can see, there's a massive increase in tracking accuracy once an auto-guider is attached!

Here's an image of the Veil Nebulae, which I captured with the help of my auto-guider.  I took about 11 images, each 3 minutes long.  Being able to shoot longer exposures helped to reveal the faint details that would have otherwise been hidden and obstructed by the camera's noise!

Picture saved with settings embedded.

Final Thoughts

If you are using a SkyGuider Pro or Star Adventurer, an auto-guider is an easy way to increase the accuracy of your star tracker!  Having struggled with 30 second exposures in the past, it was so nice to be able to shoot 4+ minute exposures!

There are some downsides to consider though.  First, you will need to bring a laptop with you from now on.  Since my laptop has terrible battery life, I also need an external battery to keep things running all night.  With all these wires dangling around in the dark, it's possible that someone may trip on one!  All things considered, you may decide that auto-guiding is not worth the hassle.  Since I do all of my deep space astrophotography right next to my car, I don't really mind.

You can also use the ZWO ASIAir Pro now.  This little device will allow you to do a precise polar alignment as well as guiding all from your smartphone, no laptop required!  It is compatible with both the SkyGuider Pro and Star Adventurer.   I personally recommend using the ASIAir for both your polar alignment and auto-guiding.  If you purchase my Deep Space Course or Star Tracker Tutorials, I will teach you everything you need to know about using the ASIAir with your SkyGuider Pro or Star Adventurer.

While the basics of auto-guiding are pretty simple, there's still a lot more to learn!  I recently created a two hour Auto-Guider Course, which is included with my Star Tracker Tutorials and my Deep Space Course. 

For more information on Auto-Guiding, check out my new tutorial video below.  This should answer most of the questions you may have.  If you want to learn even more about auto-guiders, and your star tracker, be sure to check out my Deep Space Course.  It has over 15 hours of tutorial videos!  This course has been specifically designed for DSLR users who have a SkyGuider Pro or Star Adventurer.