How to focus a DSLR camera lens on the stars
Updated: Jun 6, 2023
Astrophotography can be done without a telescope or an expensive mount. Almost every beginner astrophotographer starts out by imaging the night sky with a DSLR camera and a wide-field lens.
But if you're trying to get a magnificent picture of the Milky Way or the Orion constellation, getting the perfect focus on your lens is crucial. Focusing a camera lens during the day is completely different than focusing at night. In this tutorial, we will show you how quick and easy it is to achieve the perfect focus with any DSLR camera or lens.
For this tutorial, we will be using our Canon 7D Mark II and a 24mm lens. Make sure to watch the video at the bottom of this post if you'd like to see this in action!
Step 1 - Check Your Settings
Before even looking up to the stars, we need to make sure the settings on your camera are correct and will make the task easier. Here is what we recommend:
Mode: The Mode does not matter much since we're only going to be focusing. We suggest being in Manual or Bulb mode since you will likely be imaging after that but, as you can see in our image below, we were in AV mode that night and it did not make a difference. Just make sure you switch to Manual/Bulb mode when you are ready to image.
Aperture: Have this wide open, so the lowest possible number your lens will allow. In our case, it will be f/2.8. This will help your sensor gather more light and so you will have not problem seeing the stars. Note that after achieving focus, we usually bump that number up to f/4 in order to make sure we have pinpoint stars on the edges of our images. Refer to our Barnard's Loop episode for more info on that and a comparison of Astrophotography at different apertures.
ISO: The ISO doesn't matter too much, although it might help if you set it higher than the default number. We usually do 800 or 1600 by habit, and sometimes lower it down when we are ready to image.
Step 2 - Ensure Your Lens is Set to Manual Focus
Before actually going outside and pointing your camera up, ensure that the lens you are using is set to Manual. Do not expect to be able to focus on the star by simply using Automatic focus, that won't work, and if it does, that's just luck.
Step 3 - Locate a Bright Star and Frame It in Live View
When it gets dark enough outside, look around and try to spot one of the brightest stars. We usually aim for Vega during the Summer, and Rigel during the Winter. Planets are very bright and might also work, but those are so bright that depending on your lens, they might actually make your job more difficult. Sirius is also very bright and some people might argue that it is too bright to be used as a reference star for focusing. We would agree if focusing with a telescope, but if you are just using a lens on a camera body, Sirius is fine in our opinion.
After picking a star, aim your camera at it, at least in that general direction. Then, turn on Live View.
On your screen, see if you can spot the star or if you need to move the camera around a little bit. If you still cannot find it, start to randomly play with the focus ring on your lens. If the focus was completely off, the star might be there but just too out-of-focus to be visible.
Any of these stars will work fine when focusing your lens:
Sirius
Canopus
Rigel
Arcturus
Vega
Capella
Procyon
Altair
Deneb
Betelgeuse
Spica
Pollux
Castor
Regulus
Step 4 - Enhance... ENHANCE!
When the star sits nicely in your frame, center it and activate the maximum digital zoom allowed on your camera (usually x10) while making sure the star stays in your frame.
As you can see on our image below, our star is clearly out of focus.
Step 5 - Focus Using the Focus Ring
All you need to do now is to actually focus.
The goal is for the star to be as small as possible when looking at it through Live View.
Turn the focus ring on your lens until the star starts to shrink. Usually, you'll have to turn the focus ring all the way to one side, then backward a tiny bit. Once you achieve perfect focus, make sure you do not touch the lens during the remaining of the night.
Step 6 - Done!
You're done, your lens is correctly focused when the star will not become any smaller.
If you plan on using this lens solely for Astrophotography, it is a great idea to carefully tape the focus ring to the body of the lens after achieving focus. That way, you will not have to repeat the process again anytime you image!
We personally never used this trick as we also use our lenses to record our videos. We also don't mind having to re-focus the lenses every time we do wide-field astrophotography. Let's face it, it only takes a few seconds.
Note
Some lenses have an infinity sign on them, which tells you exactly where to stop the focus ring to achieve perfect focus on the farthest possible object.
We suggest not using that feature but rather check for yourself in the Live View because it might not be accurate enough for stars.
Final Thoughts
We hope this tutorial was helpful to you! If you are a complete beginner and are just starting out in the wonderful hobby of Astrophotography, make sure you check out our full list of tutorials!
We have dozens of tutorials that range from equipment suggestions, acquisition tips and processing techniques.
If your current goal is to do wide field astrophotography and image the Milky Way, check out our post and video about our suggestions for the Best affordable DSLR camera lenses for the Milky Way!
Below is the video version of this tutorial:
We'll see you next time for other videos and tutorials,
Clear Skies,
Galactic Hunter
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