Moon Illusion


Today’s Question: You recently had a discussion about lens compression issues, and that got me thinking about photographing the moon. Does lens compression have anything to do with the moon appearing larger when it is close to the horizon versus high in the sky?

Tim’s Quick Answer: The moon appearing larger when it is closer to the horizon is actually an illusion. However, you can make use of the concepts related to lens compression to capture a more dramatic photo of the moon when it is near the horizon.

More Detail: A full moon just over the horizon provides a more dramatic view than the same full moon high in the sky. In my view, the reason for this is that the context of terrestrial objects appearing near the moon cause the moon to appear larger. When the same full moon appears high overhead with a clear sky, the moon seems more solitary and thus smaller. The only thing that actually affects the size of the moon in the sky is how near to or far from earth the moon is at that moment, based on the elliptical orbit.

While the moon will be the same size regardless of how close it is to the horizon, the impression is that the moon appears larger when near the horizon. You can make the most of this effect and create a more dramatic photograph if you keep the concepts of lens compression in mind.

For a more dramatic image of the moon you will want to include a terrestrial object in the photo, such as a tree. That will provide context, making the moon appear that much larger.

Keep in mind that a scene can be compressed, so that the background appears closer to the foreground subject, by moving farther away from your foreground subject. That naturally means you will use a longer lens focal length to frame up your foreground subject in the same way even though you’ve moved farther away, which is why this effect is referred to as lens compression.

The key when it comes to photographing the moon is to frame the moon up with an object that is as far away as possible. For example, if you include a tree in the frame and that tree is very close to you, the moon will appear tiny by comparison. If, on the other hand, you frame the moon up with a tree that is a fair distance away, the moon will appear larger relative to the tree.

So, while the moon is near the horizon, look for a relatively distant object you can frame up alongside the moon, so you’ll have a more dramatic result with the moon appearing relatively large compared to that distant object.