4 Tips for Photographing Galaxies With a Telescope
Updated: Jun 7, 2023
Spring is coming! And it is time for you to get mentally prepared to image nothing but galaxies every night. Spring is known as Galaxy Season because most of the deep-sky objects visible high in the sky between March and late April are galaxies. If you're a nebula-lover like us, then Spring is most likely your least favorite astrophotography season.
Since you'll be imaging galaxies during these months, let us give you a few important tips to help you out! Even if you are not a fan of imaging galaxies every night for three months in a row, might as well get the best out of them :)
Below you will find four tips to get better images of galaxies. We also have a video available to watch!
1) Use a Long Focal Length Telescope
Most galaxies appear small when viewed from Earth because, despite their huge size, they are completely out of our own Milky Way and are extremely far away. If you own two or more telescopes, it is often wise to pick the one with the longer focal length when imaging galaxies. With the extra focal length, the object you are imaging will look much larger in your field of view and you will have less black space all around.
As you can see in the screenshot below taken from Sky Safari, there is a huge difference between a typical small refractor telescope (344mm FL) and a larger telescope with a focal length of 2350mm. In this particular instance with the Whirlpool (M51) galaxy, the focal length of 2350mm is perfect!
Using a telescope with a long focal length is great for imaging galaxies, but the example used (2350mm) is a little bit hardcore! A few of the best galaxies out there (the Andromeda Galaxy, the Triangulum Galaxy, the Magellan Clouds...) appear several times the size of the full moon and so cannot fit in the field of view of a very large telescope!
Look at the screenshot below. Nothing has been changed besides the object we are pointing at. In this case, Messier 31 looks great in the field of view of the small refractor, but only a tiny part of the galaxy can be seen when using the large Celestron telescope.
Still, for the majority of galaxies in the night sky, a long focal length telescope (with a great aperture of course) will be a better choice for your needs.
This was our 8" Astrograph, the largest telescope we ever owned at 800mm focal length. 800mm may not sound like much when compared to our example above at 2350mm, but it was absolutely perfect to image every galaxy in the sky!
At 800mm focal length, we were able to have a decent field of view on all popular galaxies (such as all the galaxies in the Messier catalog), and have a tight but perfect framing on the largest one out there, the Andromeda Galaxy. Be sure to visit our full blog post about M31 to see our image!
2) Use an APS-C Sensor
If you are trying to build a rig specifically for imaging galaxies, and wonder if you should get a cropped-sensor camera or their pricier full-frame counterparts, choose the cropped sensor!
The logic here is a bit similar to the first tip in this list. With a full-frame camera, your field of view will be wider and include a lot more of the space surrounding your object. This is great for large nebulae, or for photographing several deep-sky objects close to each other, but rarely needed for galaxies.
Sure, there are some groups of galaxies that a full-frame camera could capture as a whole, for example, Markarian's Chain which we captured with our full-frame camera, but there aren't that many groups of galaxies out there that are as impressive as this one.
Full-frame cameras are fantastic for astrophotography in general, but for the sole purpose of imaging galaxies, cropped-sensor cameras have a few important differences:
The size of each raw picture will be smaller
The transfer speed (if using an astronomy-dedicated camera) will be faster
Stacking each frame with processing software will be less of a struggle for your computer
Cropped-sensor cameras are usually much cheaper than full-frame cameras of similar specs
You really do not need the extra field of view when imaging most galaxies and will end up cropping it out anyway
Below you can see a comparison picture of M42 taken with both types of camera. Imagine that M42 is a galaxy with nothing but dark space all around it, and you'll quickly understand why you don't need a full-frame camera.
As of 2022, our favorite cropped-sensor color cameras for astrophotography are:
A few popular cropped-sensor cameras
3) Don't Blow Out the Core
All large galaxies, until proven wrong, have a supermassive black hole in their center.
A black hole is... black, but has such a strong gravitational pull that it attracts an enormous amount of stars towards it. The bright area you see at the center of galaxies is the combined brightness of all these stars that orbit close to the black hole.
On the right is the best picture of a black hole ever taken as of 2022. It is the supermassive black hole at the center of Messier 87.
When processing your data, be sure to not accidentally blow up the core of your galaxy! If you do not pay attention, the center of your object will be way too bright and clip a ton of pixels. This can happen when playing with Curves, the Histogram Transformation, and any other brightness tool.
A few deep-sky objects, notably the Orion Nebula or the Andromeda Galaxy as seen above, have such a bright core that it is often a good idea to take a series of short-exposure shots before or after imaging the object. You can then stack both the short and the long exposure frames together to get a nice HDR version of your object.
4) Add Hydrogen Alpha Data in Some Galaxies
Most galaxies out there are perfect broadband targets, meaning you can capture their true beauty using an unmodified DSLR camera, a One-Shot-Color astronomy camera, or a monochrome camera with LRGB filters.
Beginners might not know this, but a handful of the galaxies in the sky are also home to bright star-forming regions, rich in hydrogen-alpha gas. Do not worry, these galaxies look fantastic in broadband, but note that they can be enhanced with an added HA filter. Simply spend a couple of hours or more using the filter near the end of your session and add it all together!
DSLR Camera: Use a clip-on Hydrogen-Alpha filter
OSC camera: Use an HA filter attached to a filter drawer
Monochrome camera: Simply image with an HA filter and add it to your LRGB stack.
Below is our comparison image of Messier 106 with and without the addition of HA data. We first imaged it with LRGB filters (image on the left), and a few weeks later went back out under the stars and added some time with our hydrogen-alpha filter (image on the right). This was our very first attempt at adding HA to a galaxy, so the difference is subtle, but you can see the red star-forming regions in the galaxy's arms really nicely!
M106 without, then with hydrogen-alpha added
A few galaxies containing a great amount of Hydrogen-Alpha:
NGC 300
NGC 6946 - The Fireworks Galaxy
Want some more ideas on what to capture in Spring? Click the image below to open our guide to the best Spring Astrophotography targets!
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Conclusion
We hope that this post helped you better prepare for galaxy season! Let us know if you can think of any additional tips in the comments section and we might add them to this guide!
Clear Skies,
Antoine & Dalia Grelin
Galactic Hunter
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