Autoguiding a telescope for deep-sky imaging
Basic Autoguiding for Astrophotography Made Simple
Autoguiding is something that can be a bit daunting when you are a beginner to astrophotography. The process that takes place while guiding a telescope mount is an impressive technical feat for someone like myself, with no background in electrical engineering. It’s really not that hard, and it makes a big difference in your images.
Longer exposures mean that more light is recorded in a single frame. More light means the ability to capture fainter nebulae, galaxies, and all of the other amazing deep-sky objects that are just waiting for you to find them.
Below is a photo of a smaller, secondary telescope being used for astrophotography autoguiding:
Modern equatorial mounts are quite capable or compensating for the rotation of the Earth, that is what they were designed for. However, deep sky astrophotography is a very demanding application for any GEM. The subtle errors in the accuracy of your polar alignment become evident when trying to capture very long exposures.
The slightest bit of off- balance in your imaging rig will put un-needed stress on the mount, which leads to less than perfect stars in your long exposure image. The mount itself may have shortcomings due to worn out gears, or it just simply is not a robust equatorial mount.
Autoguiding can correct many of the issues associated with moderns GEM’s by correcting the subtle movements it makes. The use of autoguiding made a big impact on both my Celestron CG-5, (Now the Celestron Advanced VX) and my current Sky-Watcher HEQ5 astrophotography mount.
Below: My Old Celestron Advanced Series CG-5 Astrophotography Mount
Autoguiding can take your image exposures from 1 minute to 5 minutes or longer. This can really make a dramatic impact on the detail of your deep-sky objects.
Going Long (Exposure)
For example, when shooting through narrowband filters (Ha, OIII, SII), it is often necessary to shoot extremely long exposures. Shooting a 10-minute exposure without autoguiding is not possible on most astrophotography mounts without the use of autoguiding.
Personally, my exposures max out at about 5 minutes from home. If I ever invest in some stronger narrowband filters in the 6nm range, I will need to look into the potential of 600-second image frames.
What you need to start Autoguiding
The basic equipment needed to accomplish a successful night of autoguiding is a separate guiding telescope and a guide camera. The guide telescope rides atop your primary imaging telescope and is usually much smaller. The autoguiding camera is connected to this smaller telescope and your computer.
The main objective for this equipment is to focus and lock onto a star in the guide telescope’s field of view. The camera takes continuous short exposure frames and displays the “live” video feed on your computer screen.
The guide camera and your mount communicate with each other to maintain a lock on your target. This is accomplished by using a great piece of free software developed by Stark Labs.
In February 2017, I started experimenting using a new autoguiding camera. The Altair Astro GPCAM2 AR0130 Mono is an excellent choice for Astro-imagers on a budget. My early results were promising, and I may upgrade to this system in the near future.
By using an autoguiding software such as PHD2 Guiding, our computer can communicate with the telescope mount. PHD2 Guiding is the successor to PHD Guiding, which I used for several years before upgrading to PHD2. PHD stands for “Push Here Dummy”, and it very easy to use, once everything is set up properly.
In early 2017, I upgraded my autoguiding system to include a more sensitive camera, and an improved guide scope:
PHD2 Guiding includes a user interface that allows you to enter in your specific connection type and autoguiding camera model. Currently, I use a Meade DSI Pro II camera with an Orion 50mm Guide Scope. This combination has worked well for me, and I often recommend the Orion 50mm guide scope to beginners looking to start autoguiding.
- Attach 50mm Guide Scope to Primary Imaging Telescope
- Install Meade DSI CCD camera to the guide scope
- Connect PHD2 Guiding to Mount via GPUSB adapter
- Connect Meade DSI CCD to Computer via USB
- Run PHD2 Guiding
- Calibrate on Star within field of target DSO
- Run Dither function on BackyardEOS using PHD2
I use a 1-second refresh rate on the Meade DSI CCD camera to display a small number of stars within the field of view. It is important to make sure that the guide scope is properly focused to ensure accurate star tracking. Once the calibration process has been successfully completed, I like to press “stop” on the calibration star guiding. I then start the live-view up again, and begin autoguiding on another star in the frame. When PHD is running, I usually open on the “graph” window to monitor the accuracy of the tracking.
The Orion Magnificent Mini Autoguider Package is probably the best way to start autoguiding right away. This package includes the camera, the guidescope, and the mount, all for a reasonable price. In the future, I will be testing some different guiding equipment and methods. As always, I am happy to share my results.
Please consider visiting the Learn Astrophotography section of this site to explore my techniques during real-life situations in the backyard.