Get started with Deep Sky astroimaging

You have done widefield photography of the night sky using a DSLR camera and a tripod. You know how to plan and target objects to shoot and can evaluate how the object will look in the frame of your camera and telescope combination.

It's the right time to move to the next level capturing deep sky objects ( DSOs) like galaxies and nebulae. Hold tight, this is starting to get a bit complicated but as they say, no pain no gain.

Each step outlined here must be done and done well. Deep sky imaging needs precision and patience. If setting up for the first time, take your time, prioritize precision, and avoid rushing through these steps. One mistake or a step not properly done will ruin all the effort with a poor result leading to frustration.

Finally, modern astro-imaging tech is tending towards automation of many of these steps but I will focus on a more traditional approach which helps you learn in much more details and I feel is more rewarding.

Introducing the star tracker

We will still stay as simple as possible and so we will use a tripod, a DSLR camera as before, but in addition we will introduce a star tracker.

While your equipment may have some variations, I will touch upon the fundamental concepts that hold no matter what your equipment is. ( I started astro-imaging using the affordable and very popular skywatcher star adventurer 2i star tracker and I still love it. )

1. Ensure you set up the tripod at a proper place as you do not want to do all the setup only to realize that your setup does not have a proper line of sight view of the DSO. To check with reasonable accuracy you can use the sky guide app as mentioned in my previous blog. Use the time-lapse function in the app to ensure the DSO will be in line of sight for the entire duration of the shoot.

2. Align the tripod to ensure its level to the ground. Most good-quality tripods have a bubble leveler. If the air bubble is in the center of the circle, it means your tripod is level

3. Mount the star tracker on top of the tripod.

4. Slide in the counterweight bracket through the dovetail on the tracker and attach the counterweight.

5. Attach the DSLR camera to the other end of the counterweight. Suggest to begin by using the kit lens ( 18 - 55mm ) as its easier and forgiving on tracking accuracy.

6. Balance the setup on both axes ( RA and Dec ). This step is super important for accurate tracking.

And your base setup is done. ✅

Focus the camera lens to shoot sharp stars

Rough Focus

Look through the viewfinder of your DSLR and locate a reasonably far-away street lamp. Adjust the lens focus ring so that it's sharp. At a short focal length of 18mm, this is a good enough and simple approximation for focusing objects like stars. Now your focus is good enough when you point at the sky. ( You may want to take an image of the street lamp and then use digital zoom to check if the focus was good )

Change your camera settings to manual mode. You will need to tinker with these settings depending on your night sky. But these are a good start.

Shutter Speed / Exposure : BULB

ISO : 800 or1600

F-Stop as low as your camera can get

Image Type : RAW ( IMPORTANT )

Now point your camera at the part of the sky where you see a good number of stars. Ideally, if you can locate it, point it to any part of the band of the Milky Way Galaxy.

And your camera is focused and set up to shoot the night sky. ✅

Fine Focus: There is a more accurate way to focus but let's pass on that for now.

Polar Align the Star Tracker

Rough Polar Alignment

For the star tracker to work properly, we need to tell the tracker where we are and where it is pointing. Since the North Star or Polaris is on the North celestial pole, meaning the earth rotates on its axis around Polaris, we need to point the tracker at the star Polaris.

Polaris is a bright star. So point the tracker at Polaris and check if you see it through the Polar scope ( Viewer in the star tracker ). With practice, you will be able to distinguish Polaris as the brightest star in the region.

Now open the Star Adventurer App. Tap on Polar Clock Utility. You will see a grey dot somewhere in the dial. This is where you will need Polaris to be when you see through the dial through the polar scope of the star adventurer.

To shift the tracker slightly left or right use the rotating screw heads on either side of the base of the star tracker. This may seem difficult at first but with some practice, you will get used to it. As you tune one screw head one way, the other needs to be turned the opposite way. Don't worry if you think Polar is not EXACTLY at the location where it should be. At 18mm lens is forgiving on the accuracy of polar alignment. Once done, ensure both screw heads are tight.

Fine Polar Alignment: Just like focus there is a more advanced way to polar align especially needed for longer focal length lenses but we will pass on that for now.

And now your star tracker is polar aligned ✅ We are almost there.

Now power up the star tracker and select the App mode. Connect your smartphone to the star tracker wifi network. Open the app again and now connect the app to this network.

Shoot

Then in the App, now choose Astrophotography and key in the following settings.

Exposure ( Sec ) Start with 10 then increase it to 30 and then 60 and so on. You will need to experiment with exposure. Another thing to do is to see how far long you can go without overexposing the image or without introducing star trails. Note star trails should not happen when you use a star tracker. Of course, the key to not seeing star trails is the accuracy of Polar Alignment and balancing of the setup that I mentioned in earlier steps.

Photo Interval is the wait time between images automatically clicked by the camera.

DO NOT select number of photos. ( There was and probably is an issue/bug)

Tracking Rate - Sidereal

Watch how many more stars you start to see as you increase the exposure time. Of course beyond a point at a short focal length, you will start to overexpose the image likely because of city light pollution. The tracker will keep tracking the night sky and the camera will keep shooting. Stop when you want to. ( if you are stacking, the more the better, 50 images is a good start )

The Result

Here is an image I clicked with a 50mm lens on a Canon 650D DSLR on my Star Adventurer mounted on a tripod. Do you start to see the reddish nebulae? May be not in a single raw image shot by the camera but the information will be there and can be brought out using simple post-processing. In another blog, I will describe how to stack the multiple images that you took, but for now, try with only one image. If you don't see much after post-processing a single image, then try stacking all the images you took and then post-processing. I will cover this in another blog but stacking and post-processing is a fundamental step in deep sky imaging. And if you still don't see nebula, then likely you are in a light-polluted location and you will need some additional investment. I recommend this relatively cheap CLS filter which clips onto the DSLR.

Note these clip-on versions don't fit all camera lenses. There are 2-inch versions that fit the end of the lenses as well. I have a clip-on but it would only fit my 50mm prime lens.

The image I shot below shows several nebulae around the Cygnus constellation which is a stunning part of the Milky Way band that we all can see in the Northern Hemisphere.

If you have made it this far and can see nebulae, then congratulations on your first widefield shot of Deep Sky Objects!

Next, we will take our imaging to a whole new level by introducing a bit more magnification through a telescope ( we will start with 420mm refractor telescope ) or a longer focal length ( around 250mm ) DSLR lens ( Instead of the default DSLR 18-55mm camera lens ). And we will hunt for a galaxy!

As always, this is still a start. A lot of exciting things coming up. So hold tight and have patience.

Here is my kit to get these images :

1. Simple cheap entry-level DSLR camera Canon EOS T7 with its included kit lens 

2. A sturdy Tripod Manfrotto 190 Go

3. A cheap but very effective star tracker Star Adventurer 2i

4. A cheap but good telescope to start with to mount on is the Skywatcher 72ED. This telescope again is relatively affordable and is wonderful and fully capable for astrophotography. Alternatively another great option is the SVBony SV 503

5. A SVBony cheap CLS filter that really brings out nebulae. I have the one that can be inserted into my DSLR

6. A dummy batter adapter, so that you don't reply on camera batteries which can die any moment on cold nights. You will need an extension cord if you have access to power source ( I don on my back yard ) or you have to buy a power bank if you are in a totally remote location without access to a power source.

7. Finally, you may need a dew avoiding lens heater. The last thing you want is dew ruining all the effort.