Is the Moon Really That Big?

Moonrise over Trampas Peak in New Mexico.

Full moon rising over the Truchas Peaks, Sangre de Cristo Mountains, New Mexico. Real image, not a composite, taken with a 560 mm focal length lens.

Real or Fake?

Photographs with a gigantic moon can look unreal. Do we ever see the moon that large in life?

Are these “monster moon” photographs real or fake?

The short answer is that the moon can look huge in the composition when a long focal length lens is used.

Not all photographs of large moons are real though. Some photographers create the illusion of a large moon by combining two different images. This process, known as creating a “composite photograph,” merges a large moon photo with a landscape photograph. Often the two pictures are taken at different locations and times.

No worries, as long as the photographer discloses their artwork is a composite.

My preference is to not create composite photographs to portray a scene that did not exist. I love the challenge of photographing nature’s unique beauty.

However, I also understand the value of creative expression via photography.

My focus here is the science of why the moon can look large in actual photographs.

To learn more about faked photos, composites, and ethics in photography, I wrote additional some additional content: Read More

Full Moon rising over the Brazos Cliffs in New Mexico

Moonrise over the Brazos Cliffs, New Mexico. Taken with an 840 mm focal length lens. When looking through a lens this large, the moon really is this big!

Real Photographs with a Huge Moon

To make a genuine photograph with an enormous moon in the final composition, one needs to use a long focal length lens.

Ed_HarrisHawkOnLensCROP

Here I am looking through a long, fixed focal length lens (600 mm) with a large aperture of f/4. This photo was not staged. I was looking for this Harris’s Hawk (a falconry bird) in flight through this long lens. Because the angular field of view of this lens was so small, it was hard for me to find the hawk. Little did I know that it was sitting on my lens! The other camera/lens in the photo is a zoom lens, with a focal length ranging from 100 mm-400 mm.

Angular Field of View

When a long focal length lens is used, the photograph records a narrower angular field of view than our eyes see. Longer focal length lenses record a smaller region of the scene than shorter focal length lenses.

The angular field of view for our eyes is more complex than that of a camera lens system. The “sensor” of an eye is the curved retina. Both eyes contribute to the total angular field of view, and the resolution and color sensitivity is not uniform across the retina — unlike a camera sensor.

Our eyes have a relatively large field of view, about 130 degrees when we include our peripheral vision. The area where we can resolve detail and color has a smaller angular field of view of about 55 degrees, which corresponds to a 43 mm focal length lens. Although our eyes have a much larger field of view (130 degrees), much of that field of view does not see detail and color as the center of our field of view does.

When we look at the moon with our naked eyes, the moon appears small in our relatively large field of view.

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An image of the Moon formed by a long focal length lens is larger than that for a shorter focal length lens. The sensor sizes are the same in this figure (the drawing takes proper account of perspective). Note that the Moon’s angular size does not change when viewed through different focal length lenses, but the image size on the camera sensor (or film) does change depending on the lens focal length.

Comparison of angular field of view for different camera lenses looking at the moon

Two photographs were taken of the same moon, from the same location, within a few minutes of each other, but taken with different focal length lenses. The moon’s angular size, roughly 0.5 degrees, does not change when we look at it with different lenses. What changes is the field of view the camera sensor, or film, records. With the 840 mm focal length super-telephoto lens, only a fraction of the scene is recorded; however, the moon’s angular size remains at ~0.5 degrees in both photographs.

Moon over the Mount Whitney Crest

Moon over the Mount Whitney crest, Sierra Nevada, California. Taken with a 55 mm lens, not a composite. The angular field of view for this photograph is close to what the naked eye would see.

Cropping the photograph

When we crop a photograph, we discard the area we are not interested in presenting. Cropping a photographic print involves cutting the photograph’s media (e.g., with a paper cutter). Cropping a digital photograph involves selecting the image pixels of interest from the digital image file.

Discussing the size of digital images is often confusing. The best units to work in for comparing sizes of digital images are pixels. A pixel on the camera sensor is a very small light-detecting photosite that records the intensity and color of light that reaches it. A 20-megapixel camera has 20 million of these individual sensor pixels!

With a digital photograph of a moonrise, one can create the illusion of a large moon by cropping the image and then enlarging the overall dimensions of the resulting cropped image. Doing this effectively interpolates the information stored in the digital image, creating a higher image pixel density than the original image had before cropping, interpolating, and then resizing.

The two versions of the moon and West Mitten Butte are sized to have the same overall dimensions. The original un-cropped image contains the full scene; the cropped-version only shows part of the scene. Both images have the same number of screen pixels. By forcing the composition size to be the same, we effectively enlarge the moon’s size in the cropped version.

Example photograph showing the apparent size of the moon when the photo is cropped.

Moonrise Over West Mitten Butte, Monument Valley, Arizona. The top photograph is the full resolution image, showing the entire scene taken with a 100 mm focal length lens. The lower photograph is a 50% crop of the original image. When I size the outside dimensions of the two photos to be the same, the cropped image enlarges the moon, but we only see a portion of the entire image.

I do care about nature photography representing what can be seen in the natural world. When I look through a long lens or telescope at the moon, I expect it to look huge. I also expect only to see a small angular view of the landscape composed with the moon. When a photograph of an enormous moon is artificially superimposed with a landscape, it is art. When the artist discloses it as a composite photo, I know it’s art, and I can enjoy it that way. When the photographer does not disclose a composite, it is trickery—no likes for you, trickster.

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