My name is Jason Frankle (@worldpins) and I am a member of the Sony Alpha Imaging Collective. One of my favorite things to capture on a Sony Alpha camera is the night sky and deep-sky objects like the Andromeda Galaxy (M31). While many landscape photographers have captured the Milky Way galaxy, fewer have ventured into deep space astrophotography like capturing our spiral galaxy neighbor. I am often asked on Instagram if I use a telescope to capture the Andromeda galaxy but many are surprised to learn that I use a Sony 100-400mm zoom lens and star tracker. These questions led me to put together this general overview for how to capture galaxies like Andromeda on a Sony Alpha camera and lens.
Use A Star Tracker
When photographing the night sky, you may notice that stars will become blurry if you leave the shutter open for too long. This is because our planet is constantly rotating and a long enough shutter will show this movement in the form of star trails. To prevent this from happening, we need to use a star tracker (I use the SkyWatcher Star Adventurer) to counteract Earth’s rotation and keep the stars from blurring with long exposures. A star tracker sits on top of any tripod and works like an egg timer to rotate the camera and lens around the North Star (Polaris). If done correctly, the star tracker will rotate at the same rate as Earth and allow you to take exposures of up to several minutes before the stars start to blur. This is important for photographing a galaxy like Andromeda because it's around 2.54 million light years away so cameras need very long exposure times to pick up the faint light.
Align With The North Star
In order for the star tracker to do its job, it first needs to be aligned with the North Star (Polaris). Built into every star tracker is a polar scope which is essentially a small telescope with crosshairs in the middle. This mini telescope allows you to point the star tracker at the North Star so that the camera and lens can move freely with the night sky. To find the North Star, you first have to use an app like Sky Guide that shows an augmented view of the stars in the sky above. This is a great way to see what's around you at night and plan out the best time of the night to photograph. Once you have an idea of where the North Star is, position the star tracker so that the polar scope is facing in its general direction.
Next, the star tracker needs to be raised or lowered enough to see the North Star through the polar scope. This is done with an altitude adjustment knob on the star tracker. Every star tracker will have numbers printed on the altitude adjustment that match up with your current location’s latitude. For example, if you are photographing from Los Angeles, your latitude is approximately 34 degrees so the altitude should be raised to about 34 on the star tracker. There is a free app called SAM Console (for iPhone and Android) that tells you your current latitude and has a good polar clock utility. Once the star tracker is raised to roughly the altitude of the North Star, we can use the azimuth adjustment knobs to move the star tracker left and right to point the North Star in the crosshairs of the polar scope. On the SAM Console phone app, there is a polar clock utility that shows a picture of the polar scope with a black circle showing exactly where the North Star needs to be located. After the star tracker is aligned, we can mount the camera and lens on the star tracker. The camera and lens need to be counterbalanced well so that the star tracker can easily move the camera and lens.
Find The Galaxy
Now that the star tracker is aligned with the North Star, you can use the Sky Guide app to see where the galaxies are in the night sky. I generally photograph around the new moon and in a dark sky spot with lower light pollution. This will help improve the overall picture quality of the final image. Once you have an idea of where the galaxy is, pivot the camera and lens so the camera is facing the general direction of the galaxy. (Important: don’t bump the polar scope facing the North Star otherwise you will have to align the star tracker again). I recommend beginning at around a 200 mm focal length just to get the galaxy in frame. Switch to manual focus and use Sony’s manual focus assist to get the stars as sharp as possible in the viewfinder. Next, take an initial 30 second exposure to try and find the Andromeda galaxy in the sky. It will probably take several attempts to get the galaxy in frame so I usually go back and forth between the Sky Guide app and camera until I can finally see it on camera. Once you see the galaxy at 200 mm, zoom as much as your lens allows and make sure the stars remain sharp in manual focus. My current setup is the Sony 100-400mm G Master lens and α7R IV camera body which I use in APS-C mode to get an extra 1.5x crop on the sensor. This means that I can capture the Andromeda Galaxy at the equivalent focal length of 600mm while still capturing 26 megapixel RAW files thanks to the α7R IV’s ultra-high-resolution 61 megapixel sensor.
Camera Settings To Capture The Galaxy
After locating the galaxy, we can now start to capture it on the camera. To do this, I first use a remote camera shutter that will allow me to take exposures longer than 30 seconds. Set the camera to ‘Bulb Mode’ and dial in the exposure on the remote camera shutter. We can start with an exposure time of 1 minute and ISO 800 at the widest aperture the zoom lens allows. This test shot will help to see how well the galaxy will look on camera. If it’s too dark, we can either increase the exposure time to 1.5 minutes or raise the ISO. Generally, it’s best to raise the exposure time rather than ISO to limit the noise in the final image. 1.5 minutes is usually the max exposure time you will be able to do before you will start to see some star trails. This is due to tiny imperfections in the star tracker and polar alignment that get magnified when exposing for a long period of time. Generally astro photographers prevent this by using a guide scope that tells the star tracker to move slightly faster or slower to prevent star trails.
Once you can see the galaxy in frame and it’s properly exposed, take around 60 raw images (1-1.5 min each). You can set the remote shutter to take all of these images automatically. Be sure to use a lens hood to prevent dew from gathering on the lens during the 1-2 hours of exposure. After capturing the 60 images, you will need to take dark frames. Dark frames involve putting a lens cap over the lens and taking another 10-15 images with the exact settings as before. While shooting, the camera sensor can get warm and cause hot pixels to show up in the image. The dark frames allow us to see where the hot pixels are so that they can be removed later in software.
Stack & Process The Image
Now that you have the 60-80 RAW files on your memory card, it’s time to process them on the computer. To do this, I use a free program called DeepSkyStacker which is available for PCs. I use a Mac so I use Parallels to run the Windows program on the MacOS. After opening DeepSkyStacker, select ‘Open Picture Files’ and select the 60 or so RAW files you took of the galaxy. Next, select ‘Dark Files’ and select the 10-15 dark frames you took. After this, select ‘Check All’ and ‘Register Checked Pictures’. This will stack the best 80% of the image files you imported. You can increase this to 100% if you are confident that every picture you took is sharp. You can change the star detection threshold under the ‘Advanced Tab’ of the ‘Register Settings’ window and set it to around 25%. This will help the program process the image quicker. Ensure that ‘Reduce the noise by using a Median Filter’ is checked. Next select ‘Stack Checked Pictures’, set stacking parameters to Standard Mode and allow the program some time to process all of the image files together.
After the program is done processing, it will output a large TIFF file. Don’t worry if you see a dark preview of the picture above. Next we import our TIFF file into Photoshop. Start by converting from 16 bits/channel to 8 bits/channel by going to Image > Mode > and changing it to 8 bits/channel. Crop in the image slightly to reduce any stacking overlap along the edge of the picture. After this, go to the Curves tool (Image> Adjustments > Curves) and adjust it so that it bends in the middle and looks like a logarithmic curve. We can now adjust the white balance of the image by creating a new adjustment layer and pull out more detail in the picture by going to Image > Adjustments > Levels. Adjust the sliders inward just as the arrow reaches the gray bar on the diagram. Now you can go back to the Curves tool and bring out the mid-tones by lifting up at the center of the curve. Repeat this process until you are satisfied with the final result. There are many other features of Photoshop that you may use but these are the main features to focus on when starting out.
Once you are happy with the way the galaxy looks in Photoshop, you can export the image to either Capture One or Lightroom to do some final creative edits to the image. I like to use Capture One because of its great noise reduction technology. After editing, export the final JPEG image of the galaxy to your computer’s hard drive!
Note: This is an overview and general workflow for how to capture the Andromeda Galaxy using a camera lens and star tracker. Check YouTube for more in depth videos on proper polar alignment, stacking and Photoshop editing of galaxy pictures. Also feel free to message me on Instagram with any questions you have!