Autoguiding is a game-changer for deep-sky astrophotography, allowing for longer exposures and sharper images. While it might seem daunting at first, attaching a guide scope to your telescope for autoguiding isn’t overly complex. This article will break down the process and provide you with the knowledge to get started.
Understanding Autoguiding and Its Benefits
Autoguiding significantly enhances the tracking accuracy of your telescope mount. This is crucial for capturing detailed images of faint deep-sky objects. By making subtle corrections to the mount’s tracking, autoguiding compensates for imperfections and errors, resulting in pinpoint stars and revealing intricate details within nebulae, galaxies, and star clusters.
Capturing longer exposures means more light (or signal) can be recorded in a single shot. A 5-minute exposure can reveal significantly more detail than a 30-second one. Autoguiding is also useful for longer focal lengths, because we are now “sampling” a smaller area of the night sky that can potentially highlight the smallest amount of period error in your telescope mount.
This image of the Veil Nebula was captured on an affordable equatorial mount using autoguiding.
Essential Components for Autoguiding
To embark on your autoguiding journey, you’ll need a few key components:
- Guide Camera: This specialized camera captures images of guide stars and sends corrections to your mount. The ZWO ASI120MM Mini is a popular and affordable option.
- Guide Scope: A small telescope mounted on your primary imaging telescope. It provides a wider field of view for finding suitable guide stars.
- Computerized Telescope Mount with Autoguiding Port: This is essential for receiving and implementing corrections from the guide camera.
- Autoguiding Software: Programs like PHD2 Guiding or the ASIAIR app analyze guide star movements and send commands to the mount.
A simple camera and guide scope package will allow you to harness the power of autoguiding for primary imaging telescopes with a focal length of up to 1000mm. Image capture software tools like N.I.N.A, PHD2 Guiding, and the ASIAIR all have autoguiding modes to utilize this feature.
Step-by-Step Guide: How to Attach a Guide Scope to Your Telescope
- Mounting the Guide Scope:
- Using Guide Scope Rings: Most guide scopes come with rings that attach to a mounting bar or dovetail. Securely attach the rings to your primary telescope, ensuring the guide scope is parallel to the main scope.
- Piggyback Method: Some astrophotographers use a “piggyback” setup, where the guide scope is mounted directly on top of the primary telescope using a special bracket.
- Attaching the Guide Camera:
- Focusing the Guide Scope: Insert the guide camera into the focuser of the guide scope. Adjust the focuser until you achieve a sharp image of stars on your computer screen.
- Connecting to the Mount: Connect the guide camera to your telescope mount using an ST-4 cable or through a USB connection for pulse guiding. Pulse guiding (with an ASCOM-compliant) equatorial mount improves guiding accuracy.
- Software Setup:
- Installing Autoguiding Software: Download and install PHD2 Guiding or another compatible software on your computer or device.
- Connecting to the Camera and Mount: Configure the software to recognize your guide camera and telescope mount.
- Choosing a Guide Star:
- Finding a Suitable Star: In your autoguiding software, select a bright, isolated star that will serve as your guide star. The software will track the movement of this star and send corrections to the mount.
- Calibrating the Autoguider: Follow the software’s instructions to calibrate the autoguider. This process helps the software understand how the mount responds to commands.
Keeping weight to a minimum has many advantages, and a miniature system is an attractive option for beginners.
The ZWO ASI120MM Mini guide camera is affordable and works exceptionally well.
Choosing the Right Guide Scope and Camera
When selecting a guide scope, consider its focal length. As a general rule, the focal length of the guide scope should be at least one-third of your primary imaging telescope’s focal length.
The guide camera should be sensitive enough to detect faint guide stars. The ZWO ASI 290mm mini is a popular choice due to its high sensitivity and compatibility with various software platforms.
I primarily use a William Optics 50mm Guide Scope because it is lightweight and easy to mount to various telescopes.
This little telescope features the William Optics Rotolock system, a design feature that securely holds your 1.25″ barrel guide camera. I have found it very convenient to adjust the Rotolock system to move the guide camera in-and-out of the optical tube to find focus.
Troubleshooting Common Autoguiding Issues
- Poor Polar Alignment: Ensure your telescope mount is accurately polar aligned.
- Balance Issues: Make sure your imaging payload is properly balanced on the mount.
- Cable Snags: Prevent cables from snagging or pulling on the telescope during tracking.
- Focus Problems: Verify that both your primary imaging telescope and guide scope are properly focused.
Even with your polar alignment spot-on and your payload perfectly balanced, autoguiding is often necessary to track your object smoothly enough for astrophotography.
My Sky-Watcher HEQ5 Pro mount with a refractor guide scope mounted to the primary imaging telescope.
Off-Axis Guiding (OAG) as an Alternative
Off-axis guiding (or OAG) involves using a device that sends starlight to your guide camera from the optical axis of your primary imaging telescope. It does not affect your primary imaging camera, as it uses the ” off-axis ” starlight and does not enter it. An off-axis guider solves the problem of using one third of the focal length by utilizing the native focal length of your imaging telescope, but it can add weight and complexity to your camera system.
Final Thoughts: Embrace the Power of Autoguiding
Autoguiding is a valuable tool for astrophotographers seeking to capture stunning images of the night sky. While it might require some initial setup and troubleshooting, the benefits of longer exposures, sharper details, and improved tracking accuracy are well worth the effort. By following the steps outlined in this guide, you’ll be well on your way to mastering the art of autoguiding.
Also, don’t obsess about the numbers and guiding graphs within PHD2 guiding. If you are chasing numbers, chances are you’re not taking pictures. If you’re taking pin-sharp 5-minute exposures at a focal length of 1000mm or more, chances are your autoguiding system is working just fine.
