Astrophotography is probably my favorite form of photography, which is considered to be anything that involves taking pictures of the stars. What I really enjoy, and have been working on a lot more recently, is deep space astrophotography. Deep space astrophotography consists of using a long telephoto lens or a telescope to shoot a specific and small portion of the night sky. Common targets for deep space photography are objects such as nebulae and galaxies. My most recent images have been taken using my Canon Rebel T7i DSLR camera and William Optics RedCat 51 refractor telescope, which is mounted to my Sky Watcher Star Adventurer 2i tracking mount. I know that’s a lot and it probably doesn’t mean much to you, so let me explain a little better what each piece of gear is used for.
This is my setup that consists of my Canon Rebel T7i camera, RedCat 51 telescope, and Star Adventurer 2i tracker.
The camera that I use is a Canon Rebel T7i DSLR, which uses a mirror in order to look through the viewfinder. DSLR cameras are great for learning astrophotography (like myself) because they are cheaper than dedicated astrophotography cameras, and are able to be used for longer exposures over a long period of time without creating hot pixels like a mirrorless camera. I first bought my Canon T7i after I decided to get more into photography and used it as my daily shooter for about a year. After I purchased my Canon EOS R I decided to make my T7i my dedicated astrophotography camera. This camera has an APS-C sensor, which basically just means it has a 1.6x crop. So if you were to shoot with a 50mm lens on a full frame camera the focal length would still be 50mm. But with the 1.6x crop of the T7i, 50mm actually becomes 80mm. This crop sensor allows me to use my RedCat 51 telescope and shoot at 400mm instead of 250mm (which is what would happen if I used a full frame camera).
This is my Canon Rebel T7i camera body that I have used to capture all of my deep space images.
For a while I was using a 75mm-300mm lens to shoot my deep space images, but it wasn’t long until I decided to upgrade to a telescope. My telescope of choice was the William Optics RedCat 51, a small, beginner friendly telescope that instantly showed results in image quality. This telescope comes with a built-in Bahtinov mask in the lens cap (which is used for focusing), a lens hood that wraps around the focuser when not in use, and a carrying case (I upgraded to a Pelican Air hard case to transport all of my astrophotography gear). It is a simple telescope that does not require a field-flattener, which is used to counteract the natural curvature of a lens. The RedCat 51 telescope does not require one of these because it has a quadruplet Petzval optical design, which I have no idea what that means, but it makes it easier for my imaging sessions. This telescope also comes with a dovetail plate which is used to mount the telescope to the star tracker.
This is my RedCat 51 telescope by William Optics that has replaced my 75mm-300mm lens and that has taken the four photos found in this post.
My star tracker of choice is the Sky-Watcher Star Adventurer 2i tracking mount. This is an awesome and super easy to understand piece of gear that is essential to all deep space astrophotography. What a tracking mount does is rotate at the same speed the Earth orbits so that when you take long exposures of the night sky the stars don’t trail and your images are nice and sharp. In order to make sure that the mount tracks correctly it needs to be polar aligned with the North or South Celestial Pole. In the Northern Hemisphere I align with the North Star, also known as Polaris. To do this I use what is called a polar scope, which is built into the tracker itself, and place Polaris on a certain point inside of that scope. Once Polaris is on that certain point you are successfully aligned with the north pole and can start tracking.
This is my Star Adventurer 2i tracking mount that is used to capture all of my deep space images.
When it comes to tracking I tend to shoot 90 second exposures depending on the subject. If it appears clear and visible in my exposure I leave it at 90 seconds. If not then I shoot between 2-5 minutes. I try to stick with 90 seconds just because I do not have a guide scope yet, which helps the tracker be more accurate and allow for longer exposure times. Another important part in this step is getting the settings right because when you stack the images later they all must be taken at the same settings. For example, this image of the Pleiades Star Cluster was taken with the following settings: 90 second exposures at ISO 3200. The total exposure time was around 4 hours, which really helped bring out the fainter details around the stars. I also used a series of calibration frames.
My most recent image of the Pleiades Star Cluster that consists of 4 hours of total exposure time. Taken at a Bortle Class 3 Sky.
Calibration frames are divided into dark, bias, and flat frames. These are just pictures that allow the stacking software to reduce noise and overall create a clearer final image. Dark frames are taken to provide information on the electrical and thermal state of the camera sensor. These frames assist in the reduction of noise in the image, and are taken using the same exact settings used to capture your images of the night sky. It also helps to be in the same place so that the camera sensor stays the same temperature as it did taking your light frames (the photos of the night sky itself). Bias frames are also used to reduce noise, but are taken at the fastest shutter speed possible on your camera. Flat frames are used to correct unwanted vignetting and brightness variations throughout the image. These can be taken many different ways, but I prefer to put a white t-shirt over my telescope as tight as possible, place an i-Pad over the lens with a bright white light shining into the camera. These are taken at an even exposure using the exposure meter on your camera by only changing the shutter speed, not the ISO. After capturing your images of the night sky and your calibration frames it’s time to put them all together by stacking and then editing to create the final product.
Stacking is the process of combining multiple images in order to reduce noise and help bring out fainter details into one image that you edit. I use a program called Starry Sky Stacker on Mac in order to stack my images. The process is simple with just uploading the lights, darks, bias (Starry Sky Stacker does not take bias frames), and flat frames in order to pick the best images to stack for the best result. After all of my images are stacked and I have my final image, I take it into Adobe Photoshop to edit and create the final image.
To start the editing process there are a few techniques that must be done first in order to bring out more detail in the image. I start with a “first stretch” which is bringing out more faint details. I do this by adjusting the shadows and mid-tones to “stretch” the histogram out. Once I have completed my first stretch I remove the background. All I do here is create a second, blank image that is just the color of the background. I then subtract that color gradient in my final image in order to bring out a more natural looking and darker sky in the background. The final step that must be completed before anything else is a second stretch. This is really where I start to see the final image come to life with how much detail I am able to pull out in this stretch. The goal is to create a histogram that is very wide and fat to show more information. After this step is when I add brightness, saturation, contrast, vibrance, reduce the size of the surrounding stars, and create my final image.
In the sequence of images above I show the different layers I applied in Photoshop to create my final image of Pleiades.
After the finishing touches have been added all that’s left to do is sit back and admire the final product of your deep space photo. A lot of time and effort is put into these images and the best part is seeing the final product, knowing how much time, effort, and trial and error was put into capturing this deep sky object. Now I went over everything that I am using today, but it is possible to shoot deep sky objects with just a camera and lens on a fixed tripod, they just will not be as detailed and clear. If you are a photographer looking to get into this hobby I hope this helped in some way. And if you’re not then I hope you learned something about this awesome hobby and how much work goes into creating images like these.
The Pleiades Star Cluster (aka The Seven Sisters) lies 444 light years away from Earth in the constellation Taurus. This object is easily visible with the naked eye from light polluted suburbs, it just won’t appear as detailed as this.
The Orion Nebula is found in the sword of the constellation Orion and lies 1,344 light years from Earth. This nebula is a supernova remnant, meaning it is the remains of an exploded star. This object is also visible from light polluted suburbs, but again, will not appear as detailed as this.
The Horsehead and Flame Nebula found near the star Alnitak in Orion’s Belt. The Horsehead Nebula lies approximately 1,500 light years away from Earth, and is made of cold gas and dust.
The Andromeda Galaxy lies 2.5 million light years away and is our closest neighboring galaxy. This object is very difficult to see, even under dark skies. A telescope or binoculars would be best to observe this deep sky object.
