About this Post
This blog post is all about getting in-focus images of the Milky Way and your foreground subject in a single exposure, without using blending or other compositing techniques.
Find Infinity Focus
During my astrophotography workshops the first topic we cover is finding the infinity focus on the lens we will be using during the class. Many lenses are marked for infinity on the focus ring, but this should be tested to ensure accuracy. If your lens doesn’t have a marking for infinity, take the time to determine infinity focus before shooting.
To do this, manually focus your lens on the most distance object, such as a bright star (if it’s dark) or distant mountain ridge. If your camera has a “live view” feature, try using that and zoom in on your distant subject to aide in focusing. With un-marked lenses, use gaffer's tape or similar to tape your focus ring into place for the evening. Switch to manual focus if you haven't already.
Throughout your night photography shoot, instead of adjusting the focus on the camera or using auto-focus as you would in daylight, you will physically move the camera forward or back in relation to your subject to achieve focus. Since the focus is set to infinity, we know the stars will be in focus regardless of where we position the camera - that’s the goal with this method.
To recap, so far we have our lens focused at infinity and we know that any photograph we take of the sky is going to feature stars that are in focus. But what about our foreground subject? If you are too close to your subject, it is going to be out of focus and you might not be happy with the results. The solution is to back away from your subject until the subject is in focus, and then take your shot. A wider angle lens will allow you to be closer to your subject and have both the subject and stars in focus. The more telephoto the lens, the further back you will need to stand to get both the subject and stars in focus.
Math and Numbers
If you’re like me, you don’t want to spend too much time guessing where to position your camera to get the shot. Luckily, you can figure out where to position your camera to get your subject and stars in focus using a hyperfocal table, like the one in the PhotoPills app for iOS. Hyperfocal distance refers to the distance between a camera/lens and the closest object that is in focus when the lens is focused at infinity, at the given aperture setting for each different lens.
Using the PhotoPills app, you can plug in your camera and lens info, and the table will give you hyperfocal distances at various apertures for that setup. You will know exactly how far back you need to be from your subject. Keep in mind, the hyperfocal distance will change based on the set aperture and lens focal length - this is crucial for astrophotography.
Discussing Hyperfocal in Practice
As with anything, practice makes perfect, and the best advice I can give you is to go out and shoot! Enjoy the stars.
Want to learn, hands-on, how to photograph the night sky? Join me on a future workshop.
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