A Practical Guide to Automated Imaging
An interactive guide to the hardware, software, and procedures for capturing stunning images of the night sky.
1. Pre-Session Planning with SkySafari, Stellarium, and Telescopius
Before you even set up your gear, a critical step is planning your imaging session. Tools like SkySafari, Stellarium, and Telescopius are excellent for this, allowing you to select and analyze your targets for the night.
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Find Your Target (SkySafari)
Use SkySafari's powerful search and filtering tools to find a celestial object you want to image, such as a galaxy, nebula, or star cluster. You can view its position, size, and other details on the go.
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Plan with Stellarium
Stellarium's desktop application provides an incredibly detailed, high-fidelity view of the night sky. You can use its powerful search, FOV (field of view) indicators, and extensive catalogs to plan your session from the comfort of your computer.
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Use Telescopius
Telescopius is a powerful web-based tool for advanced planning. Its unique framing tool allows you to visualize exactly how a target will fit within your camera and telescope's field of view.
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Plan the Session
Based on the visibility, you can plan your imaging sequence. You'll know exactly what time to start capturing light and how long you have before the target gets too low or requires a meridian flip.
2. The Core Imaging Rig
Click on each component to learn about its critical role in astrophotography.
Select a Component
Details about the selected hardware will appear here.
Telescope
Equatorial Mount
Back Focus
Imaging Camera
Guide Camera
Focuser
Computer & Software
3. The Astrophotography Workflow
Follow the key procedures for a successful automated imaging session. Click each step to expand.
Once hardware is connected, you'll configure the software. In EKOS, create an equipment profile by selecting the correct INDI driver for each device (mount, camera, focuser) and specifying PHD2 as your external guider. Save this profile to quickly connect all your gear with a single click in the future.
Accurate alignment with the celestial pole is crucial for long exposures. PHD2 has a dedicated Drift Alignment or Polar Alignment Assistant tool. Use this tool to measure and correct your polar alignment, with the software providing real-time feedback on how to adjust your mount's altitude and azimuth knobs for the most accurate alignment possible.
A Bahtinov mask is a slotted plate placed over the front of your telescope. It creates a distinctive, three-spiked diffraction pattern on a bright star. To achieve perfect focus, you adjust your focuser until the central spike is perfectly centered between the other two. This is an extremely precise method and is often used as a preliminary step before fine-tuning with automated focusing, or as the primary focusing method for a session.
Sharp focus is essential. EKOS’s Focus module automates this process. It takes a series of short exposures and measures the Half-Flux-Radius (HFR) of stars, which is a measure of star size. By adjusting the focuser and analyzing the HFR, it finds the point of optimal focus where stars are smallest and sharpest.
To get perfectly round stars, guiding is a must. Start PHD2, connect it to your guide camera and mount, and select a guide star. PHD2 will calibrate its movement and then begin sending tiny correction pulses to your mount to keep the target perfectly locked in place, correcting for any mechanical errors or atmospheric effects.
This is where you specify your imaging plan in the EKOS Sequence Manager. You create a list of jobs, specifying the number of images, exposure length, and camera settings for the filter you've chosen for the night. You can automate advanced features like dithering (tiny movements between exposures to reduce noise) and unattended meridian flips.
4. Creating Color with a Monochrome Camera
A monochrome camera like the ZWO ASI 1600MM offers superior sensitivity. It creates color images by capturing data through different filters, one at a time, and combining them later. The common workflow is to dedicate an entire night to a single filter.
Broadband (LRGB) Imaging
This method captures images that represent the natural colors of stars and galaxies. You capture data through Red, Green, and Blue filters, plus a Luminance (clear) filter for detail, typically over several nights.
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Night 1: Luminance (L)
Capture all light for maximum detail and contrast.
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Night 2: Red (R)
Capture data for the red channel.
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Night 3: Green (G)
Capture data for the green channel.
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Night 4: Blue (B)
Capture data for the blue channel.
Post-Processing
The four separate monochrome image sets (L, R, G, B) are combined in software to create one final, full-color photograph.
Narrowband Imaging
This technique isolates specific wavelengths of light emitted by nebulae, cutting through light pollution to reveal incredible structure. The data is often mapped to RGB channels to create a "Hubble Palette" image.
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Night 1: Hydrogen-alpha (Hα)
Captures light from ionized hydrogen. Often mapped to Green.
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Night 2: Sulfur-II (SII)
Captures light from ionized sulfur. Often mapped to Red.
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Night 3: Oxygen-III (OIII)
Captures light from ionized oxygen. Often mapped to Blue.
Post-Processing
The three separate monochrome datasets (SII, Hα, OIII) are assigned to the R, G, and B channels respectively to create a vibrant, false-color image that highlights the chemical composition of the nebula.
5. Image Processing: From Raw Data to Final Image
After a long night of imaging, the real magic happens on your computer. Combining and enhancing your data is a multi-step process that removes noise and brings out the faint details of your target.
Your **"light" frames** are the actual images of the night sky, containing both the signal from your target and unwanted noise. You'll take many of these images (sometimes hundreds) to capture as much data as possible, as the noise is random and will be averaged out later.
Calibration frames are images you take to correct for imperfections in your camera and telescope system. They allow you to remove specific types of noise and artifacts from your light frames during the preprocessing stage.
- **Darks:** These are taken in a dark environment (with the lens cap on) at the same temperature and exposure time as your lights. They capture the thermal noise generated by the camera's sensor.
- **Flats:** These frames are taken by imaging an evenly illuminated surface (like a flat white screen) at the same focus position as your lights. They correct for vignetting (dark corners) and dust motes on your sensor or filters.
- **Bias:** Also known as "offset" frames, these are the shortest possible exposure dark frames. They capture the electronic readout noise of the sensor itself.
This is the first major step in software. Using programs like **Siril** or **PixInsight**, you'll use your calibration frames to "calibrate" your light frames, removing noise and artifacts. The cleaned-up light frames are then "stacked" or "integrated" into a single, high-quality master image. The stacking process aligns all the stars and averages the data, significantly improving the signal-to-noise ratio and bringing out faint details.
With your final master image, you can now begin post-processing. This involves stretching the data to make the faint nebulosity and galaxies visible to the human eye. You'll also adjust color, contrast, and sharpness. Tools like **PixInsight** are highly specialized for this, while general-purpose image editors like **GIMP** can also be used for final touches and artistic enhancement.
After processing, the final step is to share your work. In addition to being an excellent planning tool, **Telescopius** offers a great platform for hosting your astrophotography. You can upload your final images, and the site even helps with plate solving to identify the objects in your shot. Other popular community sites for sharing and getting feedback include **Astrobin** and **Flickr**.
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