Deep Sky Astrophotography Step-by-Step Walkthrough
In this post, I’ll break down everything you need for deep sky astrophotography with a telescope. I’ll cover each piece of gear I use, and explain how it can be used to capture beautiful deep-sky images of space from your backyard.
Deep-sky astrophotography is a rewarding and fulfilling hobby, especially once you’re able to achieve impressive results from your own home. This post aims to give beginners a better idea of what you need, and what you can expect to accomplish yourself.
I’ll be setting up from scratch, and talk about each piece of gear used, so you can replicate my process. I’ll warn you right now, my methods are by no means “the right” way to do this, it’s just the way that works for me.
Deep Sky Astrophotography Walkthrough
The following video takes you through my current deep sky astrophotography routine step-by-step. For a more detailed description of the process, keep reading!
A long exposure photo of 1-minute or more will collect much more light on an object in space than you could ever see with your naked eye alone. This detail is collected onto the camera sensor, and can then be processed to pull out even more color and detail.
When it comes to deep-sky astrophotography, you can consider the telescope to act as the camera lens. The focal length and aperture offer you the power needed to get a close-up look of some incredible deep-sky objects in space. In general, the most important aspect of deep-sky astrophotography is to collect as much data as possible – good data.
It needs to be sharp, well exposed, and well framed. With good data, the image processing stage is a lot of fun. With enough overall exposure time, your image will benefit from a strong signal-to-noise ratio.
You can learn more about the basics of deep-sky astrophotography in the “get started” section of this website. For now, I’ll focus on what you need to start capturing quality data from home.
Before Getting Started
The last thing you want to do is spend time carefully setting up all of your gear on a night when the weather forecast is not promising. I usually don’t set up my equipment unless I am confident the sky will be clear until dawn. I monitor a variety of weather forecasting apps to see if the sky will be clear during the night from my location.
I have found that the most accurate tool to forecast a clear night sky is Clear Outside by First Light Optics. I use the Android app version on my smartphone. The app includes several useful metrics including visibility, wind direction, estimated sky quality and more. I like the low, med, high cloud format and have found it to be astronishly accurate.
The Clear Sky Chart is another great tool to use, but I find the forecast to be a little optimistic for the most part. Often times, the forecast looks better on the clear sky chart than it does on Clear Outside. This tool is an online webpage rather than an app, but it has an impressive amount of locations across the world listed. Just Google your location + clear sky chart.
Step 1: Powering the Gear
We need to power the equipment, so I usually run an extension cord (or two) out to my imaging location in the backyard. Many people use a portable battery pack to power their gear, and so do I when I don’t have access to electricity.
You can save some serious cash by building your own battery pack using a deep-cycle marine battery and an inverter. I bought one of those battery booster packs from the hardware store for convenience – but they don’t last long and are overpriced.
The model I use is a Motomaster Eliminator 600W (Similar to this style) and it has enough juice to power all of my equipment for 1 night. After that, it’ll need another full charge to reliably go another night. I’ve had batteries die on me in the past, and it’s a heartbreaking moment.
Step 2: Level the Tripod Mount
An astrophotography telescope mount must sit on a tripod, or in my case a tri-pier. A rock-solid base for the equatorial tracking head of the mount is essential. You’ll need to confirm that it is level and secure to avoid headaches later on.
Many people build a custom concrete pier and fasten their tracking mount to it for the ultimate stable platform. This, of course, requires a permanent spot for your equipment. I’ve thought about constructing a small observatory in my yard, but I’ve decided to wait until I have a little more property to work with.
No matter what size of tripod or pier you use for astrophotography, you need to make sure that it won’t slip or move throughout the night.
Step 3: An Equatorial Mount
Many astrophotography mounts include a built-in bubble level, which comes in really handy if you often set up in new locations. For the current mount that I use, I simply adjust the length of the tri-pier legs until the mount head is as level as possible.
The astrophotography mount I currently use is an iOptron CEM60, which was generously loaned to me from Ontario Telescope and Accessories. It’s a center-balanced equatorial mount that uses a magnetic gear system.
The mount moves the telescope in 2 axis, right ascension (RA) and declination (Dec). It allows me to point at any deep sky object that isn’t obstructed by trees or houses in my backyard.
Once it’s centered on the object, it will track it and keep it completely still so I can photograph it. (Autoguiding improves this, but I’ll cover that momentarily) The iOptron CEM60 is a GoTo mount, which means that I can enter the target name into the keypad, and then the mount will slew the telescope to it for me.
Recommended Telescope Mount Options:
Entry Level: Orion Sirius EQ-G Computerized Telescope Mount
Intermediate: iOptron CEM60 Center-Balanced Equatorial Telescope Mount
Professional: Software Bisque Paramount ME II
Step 4: Polar Alignment
An accurate polar alignment is crucial for a successful deep-sky astrophotography image. The process of polar-aligning a telescope mount for astrophotography may sound difficult to achieve at first, but it’s really not that complicated.
The reason I mention it at this stage, is because you’ll need to roughly have your telescope mount polar aligned when setting it up. Meaning, the counterweight shaft should be pointing directly north. Because I am in the northern hemisphere, I use Polaris, the north star, as a guide to accurately polar align the mount.
If you live in the southern hemisphere, or can’t see Polaris, there are alternative ways to polar align. Software assisted methods such as drift alignment can help. I’ve used a polar alignment routine in a program called SharpCap. PHD2 guiding (which ill cover shortly), also has a useful drift alignment tool.
The way I do it, is to use a simple app on my phone (PolarFinder) to tell me exactly where Polaris needs to be in my polar finder scope to be polar aligned from my location. It uses my GPS coordinates and places the star in the correct position for my exact location and current time.
Then, it’s just a matter of matching up what the app tells me on the mount be adjusting the alt-az knobs. The entire process should only take about 2 minutes once you are used to it. If you’re really not interested in this manual process, or cant see Polaris. You should probably check out the QHY PoleMaster.
Using the QHY PoleMaster to accurately polar align my telescope mount.
Step 5: Balancing the Telescope
Now that we’re polar aligned, we can get to the fun part – mounting the astrophotography telescope. Along with being polar aligned, balance is a major factor to consider when setting up your rig.
All equatorial mounts include a counterweight, which I’ll need to use to balance this 20-pound refractor telescope. You need to balance the scope in both axis, so that the mount doesn’t have to work any harder than it needs to when slewing and tracking objects in the night sky.
The telescope I’ll be using tonight is a William Optics Fluorostar 132. It’s an apochromatic triplet refractor, which is one of the best telescope types to use for the purposes of astrophotography. It has a focal length of 925mm and an f-ratio of F/7.
A telescope like this has enough aperture to pull in some serious light and get an up-close look at some of the most impressive deep sky nebulae.
We need to attach the imaging payload (the camera) to the telescope, along with the autoguiding system for an accurate overall weight to balance. This is the payload that will need to be tracking smoothly while the photos are being taken. Even the distance the focuser is from the tube will make a difference in the balance, so there may be some trial and error here.
The closer your imaging payload is to the maximum capacity of your mount – the more balance comes into play. For reference, the CEM60’s 60-pound payload capacity is very forgiving with my relatively light 25 lb imaging gear.
In general, your mounts payload capacity should ideally be double the weight of your astrophotography gear. This may seem excessive, but long focal lengths and long exposures demand the greatest of tracking accuracy. If you haven’t taken the time to balance your telescope, even the slightest imbalance may come back to haunt you over time.
Step 6: The Imaging laptop
There have never been so many great options for controlling your camera or mount remotely for astrophotography than there are now.
Dedicated astrophotography computers, mini pcs, and good old-fashioned laptops. I’ve been using the same laptop since I started taking images of space back in 2011. It runs Windows 7, and all of the astrophotography software needed to run a successful imaging session.
The Astrophotography Software I Use:
- Astro Photography Tool
- PHD2 Guiding
- iOptron Commander and ASCOM driver
- SharpCap Pro
- Cartes Du Ciel
- Team Viewer
The computer has software installed for controlling the camera, the mount and of course an internet connection. I can remote in to this laptop from in the house using Team Viewwe to check up on things from inside the house.
Step 7: Autoguiding Setup
Now, let’s talk about this smaller telescope riding atop the big one. This is called a “guide scope”, and its job is to help the mount track with even greater precision.
I’ll attach a small camera into this telescope, which will feed an image to my computer with a looping image of stars. Then, my computer will communicate with the mount to make small adjustments in periodic error for improved tracking accuracy.
It sends guide pulses to the mount to based on the tiny movements it read from the guide star. This is called autoguiding, and it can be the difference between the ability to capture a 30-second exposure and a 5-minute exposure.
For my upcoming task of star alignment, I’ll use an eyepiece in this little telescope before attaching the camera. It’s a 32mm eyepiece – that offers a 52-degree wide field of view. This is beneficial for the next step of my process.
Step 8: Star Alignment
With the mount leveled, polar aligned, and the telescope balanced. We can actually turn this sucker on. With this mount, I need to first set the “zero position“, with both axis in the home position.
After that, I’ll begin a simple star alignment routine that calibrates the mount to have precise pointing accuracy.
This means that when I punch in the deep sky object I want to image, I can be sure that the telescope will land on it and put it dead center in the frame.
Certain objects are extremely dim, so it would be impossible to know if I have the telescope pointed at it without taking a series of test exposures. This can take precious time away from imaging on a clear night – so take the time to properly star align your mount first.
I personally don’t mind this stage of the process, because I honestly enjoy a little time actually looking through the telescope and getting some minor physical activity.
But I understand that there are those of you out there that are either tired of this process or have mobility issues. For these folks, I suggest using a plate solving software aid such as Astro Tortilla.
The manual process of star alignment involves slewing to 2 or 3 bright stars and centering them in first the guide scope, and then through the primary imaging telescope. Since I’ll be pointing at some of the brightest stars in the sky, I like to perform my focus routine at the same time.
Step 9: Focus and Camera Control
I like to use the live-view image from the camera during star alignment to help center the stars. Rather than centering the star in an eyepiece, I’ll jump into my camera capture software to make this process easier and more precise.
The software is called Astro Photography Tool (APT for short).
The Astro Photography Tool Camera Control Software Interface
A camera control software like this not only lets you automate the length of each image and number of shots to take, but they also include features to help with focus, framing, and much more.
A dedicated astronomy camera like the one I’ll use tonight does not include a display screen with an image the was a DSLR does. This means that running an additional software tool to run the camera is necessary.
To focus, I use a tool called a Bahtinov mask that creates a star diffraction spike pattern on stars that are close to being focused. During my 3-star alignment routine, I roughly center the star in the wide field guide scope visually, and then use the live-view loop with the Bahtinov mask to both center the star in the primary imaging scope, and set my focus.
What you’re aiming for is a centralized spike between the X. Next, I’ll talk about the camera itself.
Once you’ve found the best focus possible using the Bahtinov star diffraction spike method, you can lock the telescope focuser in place using the thumbscrew in the underside of the tube. Don’t forget to take the Bahtinov mask off before capturing your light frames! (I’ve made this humbling mistake before)
To retain focus throughout the night, you may need to re-focus later on, especially if the temperature has dropped significantly. A motorized focuser such as the Pegasus Astro model I demoed over the winter makes this task much easier by allowing you to make micro-step adjustments via software on your computer.
Step 10: Setting an Imaging Sequence
With the star alignment and focus routine out of the way, we can now slew to our deep sky target for the night.
Certain targets are better choices than others depending on your imaging conditions, moon phase, camera sensor size, telescope, filters etc. Over time, you’ll learn what you particular gear is best at, and set your self up for success whenever possible.
The camera I am using tonight is known as a one-shot-color camera. It shoots images using in broadband true color, using a sensor that collects light in RGB simultaneously. A monochrome camera is capable of collecting more signal (light) at once, but a filter wheel is needed to conveniently capture each color channel needed to produce a full-color image.
This camera is called the ZWO ASI294MC-Pro. It includes a cooling feature that keeps the internal sensor cold during long exposures. This is important because a hot sensor means more noise. Noise is the little pixels and artifacts that can really make a mess of your image. With a cool sensor, you’ll be able to create images with a much better signal-to-noise ratio.
The ZWO ASI294MC-Pro One-Shot-Color Camera
For those shooting with a DSLR camera:
If you’re shooting deep sky astrophotography with a DSLR, the process is slightly different than the way I have featured in the video. This is particularly evident when it comes to the focus, framing and imaging sequence setup.
With the DSLR attached to the telescope via a t-ring and adapter and/or field flattener (these adapters are usually 0.8X and both reduce the focal ratio of the telescope, and “flatten” the field of view), you’ll want to frame up your target just as you would with a dedicated astronomy camera.
The camera and telescope will need to be in focus before attempting to frame your target, and you have a few options here. One option is to focus on a star using live view on the camera itself before connecting to APT. A high ISO (1600+) is recommended while focusing and framing as it will produce the brightest stars for reference purposes.
You could also use the “live view” mode in APT. A short exposure of 4-5 seconds should be long enough to focus using a Bahtinov mask. Then, you can use a longer exposure loop to frame your deep sky object.
Set the exposure length to about 5-10 seconds, using an ISO of 1600 or more. (6400 works well for this step). This should pull in enough stars too orientate your subject, even with a strong filter in front of the sensor. (Such as a clip-in Ha filter)
Step 11: Recommended Filters
From my city backyard, filters are necessary to capture any sort of usable image. If I want to shoot a true-color image with this camera, a light pollution filter will help ignore many of the wavelengths of light associated with things like streetlights and porch lights. My backyard is located in the center of town, rated a class 8 on the Bortle Scale.
Even then, extensive image processing must be done to separate the deep sky object from the bright sky. It’s the price we pay for being able to enjoy this incredible hobby from the comfort of our backyards.
Tonight, I’ll be shooting with a much stronger filter. It will ignore all wavelengths of visible light except for 2 very narrow bandpasses.
The STC Astro duo narrowband filter collects the light associated with Hydrogen-alpha and Oxygen only. For certain emission nebulae, it can produce jaw-dropping images in even the heaviest of urban light pollution.
The Eagle Nebula using the STC Astro Duo-Narrowband Filter
Step 12: Slewing to Target
With everything balanced, aligned and ready to go, we can now hop into the camera control software to set up an imaging sequence.
The target I have chosen to shoot is the Butterfly Nebula in Cygnus. It rises above my house by 10 pm and I ‘ll track it along the sky until morning. I’ll need to perform a meridian flip when the mount reaches the Zenith, which just means the telescope needs to switch sides and start tracking again.
For narrowband images like the one I’ll share in this post, you’ll want to use a longer exposure than you would when shooting in color.
I’ll tell the software to shoot 40 x 6-minute images. To make sure that each one of these 6-minute subs is sharp, I’ll turn on the autoguiding system.
Step 13: Autoguiding
For autoguiding, I use a free software called PHD2 guiding. This tool runs my little guide camera, the Altair Astro GPCAM2. It houses a small mono sensor with one job – to follow a single star all night.
The software will communicate with the mount to make the small adjustments needed for improved tracking accuracy. I can also leverage a feature called dithering, which reduces overall noise in your stacked image by slightly shifting the position between each frame before capturing.
A way to know if your guiding is “good” or not is to view the graph tool in PHD2 guiding. A smooth graph will have a total RMS error under 1 second, as seen in the screenshot below.
Helpful resource: Analyzing PHD2 Guide Logs
Step 14: Capture Your Deep Sky Target
Here are the individual steps I take to set up a complete imaging sequence in APT with PHD2 guiding.
- Connect camera (ASI driver)
- Choose “unity gain” setting
- Connect mount (iOptron Commander)
- Use live-view with Bahtinov mask
- Center 3-star alignment stars
- Focus on alignment star using star diffraction spike pattern
- Remove Bahtinov mask
- Slew to target
- Set cooling to -20 (Cooling-Aid)
- Slew to target
- Adjust target framing using 20-30 second live view loop
- Run and calibrate PHD2 guiding
- PHD2 guiding with smooth graph
- Ensure dithering is active
- Start imaging plan (eg. 30 x 300-second subs, Binned 2×2)
- Grab a beer and watch each image appear!
Here is the image I captured using this setup on the night I recorded the video. The image includes just over 6 hours worth of total integrated exposure time using 6-minute images.
After collecting all of my light frames for the image, I took 20 dark frames that I’ll use during the stacking process. Dark frame subtraction is the process of defining the digital noise crated by the camera sensor, and removing it from your final image.
The images were stacked in DeepSkyStacker to improve the signal-to-noise ratio before being processed in Adobe Photoshop to pull out more color and detail.
The Butterfly Nebula is located in the Sadr Region of Cygnus, and it an excellent astrophotography target to capture in narrowband hydrogen-alpha.
If you’re brand new to astrophotography, I hope you now have a better understanding of the process involved in capturing deep sky objects through a telescope. It may seem like a lot to take in all at once – because it is!
The good news is, if you are dedicated and passionate about astrophotography, small victories and improvements along the way are all you will need to keep going.
I certainly didn’t get to where I am at today in a hurry. Why would I rush through something I absolutely love doing?
My final advice to you would be to be patient and remember to enjoy each small victory along the way. The night sky is not going anywhere, and you have the rest of your life to explore it.