Autoguiding for Deep-Sky Astrophotography

For long exposure astrophotography of Deep-Sky Objects, autoguiding is a must. Keep reading to learn what Autoguiding is, and why you need to do it.

Equatorial (EQ) Mounts & Deep-Sky Astrophotography

If you’re someone who already has an Equatorial (EQ) Mount, you might be wondering:

“My EQ mount already tracks deep-sky objects over long-exposures. Why do I need auto guiding?”

Good question.

As someone deeply passionate about astrophotography, I cannot stress enough the significance of having an Equatorial Mount to capture breathtaking images of the night sky through a telescope. This applies particularly for astrophotography over longer exposures for deep-sky objects.

EQ Mounts play a critical role in compensating for the Earth’s rotation, enabling us to accurately track celestial objects. However, even the finest Equatorial Mounts possess inherent tracking errors due to mechanical imperfections in their gears and bearings. These errors can lead to elongated stars and blurry deep sky objects over long-exposures.

While Equatorial Mounts track accurately for short exposures of 30 to 60 seconds, they often require assistance to maintain precise tracking for exposures lasting several minutes. This is where Auto Guiding comes into play.

Saxon AZ-EQ6 Equatorial Mount with hand controller, tripod and counterweights for deep-sky astrophotography
Saxon AZ-EQ6 Equatorial Mount

Limit Periodic Errors with Autoguiding

As an avid astrophotographer, I’ve come to realize that even the best quality mounts, equipped with advanced features like Periodic Error Correction (PEC) and perfect alignment, still exhibit slight imperfections that can impact the quality of high-magnification imaging. These imperfections come from inherent flaws in the drive gears and other mechanics of the mount, such as the precise alignment of the Declination and Right Ascension Axes or the tolerance in the ball bearings responsible for smooth rotation.

These residual errors are known as Periodic Errors (PEs). Although minor, Periodic Errors can lead to subtle movements of targeted celestial objects over long-exposures, especially when using long focal-length telescopes like Schmidt Cassegrain Telescopes. Even with meticulous mount alignment, these errors can cause stars to transform from pinpoint dots into small streaks over extended exposures lasting several minutes.

This is where auto guiding comes in.

What is Autoguiding?

Autoguiding is a technique that minimises these minor residual errors in an otherwise well-performing mount, reducing it to an acceptable level. By autoguiding, tracking will be precise during long-exposure astrophotography, ensuring that stars remain as crisp points of light throughout the exposure.

Periodic error analysis on a Skywatcher HEQ5 Equatorial Mount
Periodic Error Analysis on a Sky-Watcher HEQ5 Equatorial (EQ) Mount

Do I Need Auto Guiding for Lunar or Planetary Imaging?

Autoguiding specifically benefits long-exposure astrophotography, particularly of deep-sky objects. If your primary focus is lunar or planetary imaging, where multiple short exposures are combined to create the final result, auto guiding is unnecessary. Similarly, if you’re capturing photographs of the Moon with exposure times no longer than a few seconds, auto guiding is not required.

How Does Autoguiding Work?

The process of Autoguiding involves making small corrections to the position of an Equatorial Mount during long-exposure astrophotography of deep-sky objects.

By using a guide camera and specialised software, you can monitor the position of a nearby ‘guide star’ relative to the object you’re imaging. The software then automatically adjusts the mount to keep the guide star in the same position and maintain accurate tracking. This continuous, real-time adjustment eliminates the elongation and blurring caused by tracking errors, resulting in sharper and more detailed images of deep sky objects.

Auto guiding is a game-changer for astrophotographers seeking to capture stunning images of deep sky objects during long-exposure sessions. By mitigating the minor residual errors present in mounts, auto guiding ensures accurate tracking, allowing for the capture of intricate details and the preservation of pinpoint stars. It’s an invaluable tool that will elevate the precision and quality of your astronomical photographs.

Autoguiding Equatorial Mount Setup for Deep-Sky Astrophotography
Equatorial Mount Setup for Autoguiding

What Equipment Do I Need for Autoguiding?

Guide Cameras for Deep-Sky Astrophotography Autoguiding

Autoguiding requires the use of a separate guide camera. Here are a few great options to consider.

ZWO ASI1200MM Mini USB 2.0 Mono Guide Camera

Price: $259.95

ZWO ASI1200MM Mini USB 2.0 Mono Guide Camera for autoguiding during deep-sky astrophotography

The ZWO ASI120MM Mini USB 2.0 Mono Guide Camera is a popular and affordable choice for beginner imagers.

Pixel Size: 3.75 μm

– 4.77″ Per Pixel with a 162mm Focal Length Guide Scope
– 3.22″ Per Pixel with a 240mm Guide Scope

These resolutions are more than adequate for deep-sky astrophotography autoguiding under typical seeing conditions. Despite a resolution of 1 MP, the camera works well with a short focal length guide scope for selecting guide stars. Its read noise, rated at 4e, prevents hot pixels from being mistaken as stars during autoguiding.

The mini version offers a frame rate of 35 FPS, which is suitable for most users’ 1-second exposure guiding needs. The camera’s 2.0 USB connection ensures efficient communication with your laptop or PC and mount. With a 75% quantum efficiency, 12-bit Analog-to-Digital Converter, and 13k Full Well Capacity, the ASI120MM mini performs exceptionally well for autoguiding. It can even be used for basic lunar and planetary imaging.

Overall, this compact and budget-friendly CMOS camera excels as an autoguide camera with its monochrome capabilities, pixel size and resolution. Despite some modest specifications in read noise and framerate, it proves to be more than sufficient for autoguiding and offers reliable performance.

QHY 5L-II-M CMOS Guide Planetary Astronomy Camera – Monochrome

Price: $223.97

The QHY 5L-II-M CMOS Guide Planetary Astronomy Camera (Monochrome) is a great alternative to the ZWO ASI120MM Mini.

Pixel Size: 3.75 μm

Resolution: 1.2 MP (1280 x 960)

QHY 5L-II-M CMOS Guide Planetary Astronomy Camera - Monochrome with ports visible for autoguiding

QHY has similar cameras on the market with comparable sensors and specifications to the ZWO cameras I’ve mentioned in previous blogs.

What’s great about having multiple brands in the market is that we have the freedom to choose based on factors such as price and availability. It’s wonderful to have options that cater to different budgets and preferences.

Ultimately, when deciding which camera to purchase, you can consider both the prices and availability of the different brands. It’s fantastic to see that there are affordable options available from various manufacturers, allowing us to make the best choice for our individual needs.

ZWO ASI290MM Mini USB 2.0 Mono Guide Camera

Price: $499.95

ZWO ASI290MM Mini USB 2.0 Mono Guide Camera pointing right for autoguiding during astrophotography of deep-sky objects

The ZWO ASI290MM Mini USB 2.0 Mono Guide Camera is a step above the ASI120MM Mini, offering improved performance.

Pixel Size: 2.9 μm

Resolution: 2.1 MP (1936 x 1096)

With a smaller pixel size of 2.9 μm, the ZWO ASI290MM Mini provides enhanced resolution for precise tracking of celestial objects. It has a 2.1 MP resolution, and a low read noise (1e), making it suitable for autoguiding as well as planetary and lunar imaging.

The camera has a frame rate of 20 FPS, a 2.0 USB connection, ST4 guideport, 12-bit ADC, high quantum efficiency (80%), and a full well capacity of 14.6k. This makes it great for deep-sky astrophotography autoguiding.

If planetary imaging is a priority, there are pricier versions available from ZWO and QHY with higher frame rates (up to 170 FPS) and USB 3.0 connection.

ZWO ASI174MM USB3.0 Monochrome CMOS Camera

Price: $949

The ZWO ASI174MM USB3.0 Monochrome CMOS Camera is highly-regarded by astrophotography enthusiasts – and for good reason.

Pixel Size: 5.86 μm

Resolution: 2.3 MP (1936 x 1216)

ZWO ASI174MM USB3.0 Monochrome CMOS Camera for Autoguiding during Deep-Sky Astrophotography

The ZWO ASI174MM USB3.0 Monochrome CMOS Camera steers away from the compact mini style.

This advanced CMOS astronomy camera combines exceptional performance with user-friendly features. Priced at $949, it falls into the higher-range price category but still offers excellent value for its capabilities.

This camera also has a frame rate of 20 FPS, a 2.0 USB connection, ST4 guide port, 12-bit ADC, high quantum efficiency (80%), and a full well capacity of 14.6k.

Featuring a 2.35 MP resolution (1936×1216), the ZWO ASI174MM USB3.0 Monochrome CMOS Camera delivers impressive image quality. With a pixel size of 5.86 μm, it achieves a pixel scale of approximately 0.39″ per pixel when used with a typical telescope. This level of resolution allows for capturing fine details in celestial objects.

One standout feature of the ZWO ASI174MM is its high quantum efficiency. With an impressive rating of 78%, it ensures optimal light capture, resulting in images with enhanced brightness and clarity. This makes the camera well-suited for both deep-sky imaging and planetary photography.

Overall, the ASI174MM is a top choice for astrophotographers seeking high-quality images and reliable performance. Its impressive resolution, quantum efficiency, low read noise and advanced features make it suitable for various astrophotography applications. Whether you are capturing breathtaking deep-sky objects or observing the intricate details of planets, this camera is sure to deliver outstanding results.

If planetary imaging is a priority, there are pricier versions available from ZWO and QHY with higher frame rates (up to 170 FPS) and USB 3.0 connections.

Guide Scopes for Deep-Sky Astrophotography Autoguiding

For Autoguiding for Deep-Sky Astrophotography, you will also need a Guide Scope to suit your Guide Camera. Here are the Guidescopes I recommend.

saxon 50mm Guidescope with Helical Focuser

Price: $214.95

saxon 50mm Guidescope with Helical Focuser for autoguiding during deep-space astrophotography

The saxon 50mm Guidescope with Helical Focuser is a good choice that won’t break the bank.

Aperture: 50mm
Focal Length: 190mm
Focal Ratio: f/3.8

This little gem is one of the most affordable scopes available today, priced at a little over $200. I’ve had the pleasure of using this mini-scope for years, and it has never failed to impress me.

One standout feature is its solid Helical Focuser, which works like a charm when it comes to focusing your guidescope on those distant stars. With smooth adjustments, achieving pinpoint focus becomes a breeze.

It also comes equipped with a robust mounting ring, providing a secure and worry-free attachment for your camera. During my imaging sessions, I never experienced any troublesome movement of the guide camera within the guidescope. And did I mention that it weighs in at only 500 grams?

This mini-scope has proven itself in the field, guiding successfully at focal lengths of up to 1500mm. That’s no small feat! However, I would recommend sticking to focal lengths of up to 1000mm for optimal performance. If you’re looking to push beyond that limit, it might be worth exploring options like an off-axis guider (which I will cover in a later blog) or one of the longer focal length guidescopes.

ZWO 30F4 Mini Guidescope

Price: $169.95

The ZWO 30F4 Mini Guidescope offers several key features that make it a compelling option for deep-sky astrophotography.

Aperture: 30mm
Focal Length: 120mm
Focal Ratio: f/4.0

ZWO 30F4 Mini Guidescope pointing left for autoguiding during deep-sky astrophotography

First and foremost, the ZWO 30F4 Mini Guidescope is designed with a focal length of 120mm and a fast focal ratio of f/4. This combination allows for a wide field of view, making it easier to locate and track guide stars. With a large field of view, you can effectively guide your telescope with greater precision, ensuring accurate tracking of celestial objects.

It also has a Helical Focuser.

The guide scope is sturdy and durable, ensuring stability during imaging sessions. It features a lightweight aluminium tube, minimising the overall weight of your setup while maintaining strength and rigidity. This portability makes it convenient for both on-the-go astrophotography and permanent installations.

To further enhance its functionality, the guide scope is compatible with various guide cameras, including ZWO’s ASI series and other popular models. This versatility allows you to choose the camera that best suits your needs and preferences, ensuring seamless integration and optimal performance.

Overall, the ZWO 30F4 guide scope is an attractive option for astrophotographers seeking a reliable and versatile tool for guiding their telescopes. With its wide field of view, sturdy construction, and compatibility with a range of guide cameras, it offers a compelling solution for capturing stunning images of celestial objects by autoguiding deep-sky astrophotography sessions.

Skywatcher EvoGuide ED50 Guide Scope

Price: $449.95

Skywatcher EvoGuide ED50 Guide Scope pointing right for autoguiding during deep-space astrophotography

The Skywatcher EVOGuide ED50 Guide Scope offers excellent colour correction with ED Glass.

Aperture: 50mm
Focal Length: 242mm
Focal Ratio: f/4.8

The Skywatcher EVOGuide 50ED Guidescope has a unique twist. It may seem a bit pricey at first as its focal length (242mm) and aperture (50mm) aren’t extraordinary.

However, what sets it apart is its high-quality FPL53 ED Glass and Doublet Configuration, which ensures excellent colour correction. This feature might not be crucial for guiding alone, but here’s where it gets exciting: you can actually use this scope for Main Imaging purposes as well.

Yes, you read that correctly. With the EVOGuide and a camera, you can capture impressive wide-field images of the night sky. It’s not just a guide scope; it’s a versatile tool that allows you to venture into widefield imaging sessions, even in remote locations.

The scope comes with two rings and a dovetail bar, ensuring a secure setup on your primary telescope rig. When you consider the EvoGuide’s potential as both a guide scope and an imaging instrument, it becomes a worthwhile investment.


To wrap things up, I hope this comprehensive overview has provided you with valuable insights to assist you in selecting the ideal guide scope and camera for your astrophotography journey. Remember, you don’t need to break the bank to achieve deep-sky astrophotography autoguiding.

In conclusion, whether you opt for the more affordable options or decide to venture into higher-quality territory, there are ample choices available for deep-sky astrophotography autoguiding.

Whatever you choose to go with, remember to look up and enjoy the wonders of the universe.

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