This stunning moonrise is an optical illusion

Illustration for article titled This stunning moonrise is an optical illusion

Holy crap. This, everybody, is a Moonrise. The image was captured last week in Cape Sounion, Greece, by photographer Chris Kotsiopoulos, and it's one of the most mindblowing images of the Moon we've seen in in quite some time. Just look at it looming there — it's freaking enormous!


So how did it get to be so big?

The visual effect that Kotsiopoulos achieved here is two-fold. For starters, he's managed to catch the quarter moon right above the horizon, giving rise to what is sometimes referred to as "the Moon Illusion."

The Moon Illusion is really just nature's twist on the age-old Ponzo Illusion, and Phil Plait does a great job of explaining it (while showcasing his formidable Photoshop abilities) over on Bad Astronomy, so I'll leave that to him. But most of us have witness the effects of the Moon Illusion before, and have never seen the Moon look quite this big — so what gives?

Remember how I said the effect here was two-fold? A little digging led me to Kotsiopoulos' website, where I discovered the file data for the photograph:

Canon EOS 550D, SW ED 80, 15/3/2012 2:03, Shutter Speed 0.5 sec, Aperture Value 7.5, ISO 400, Focal Length 600 mm [emphasis added]

Illustration for article titled This stunning moonrise is an optical illusion

Bingo. The number we're looking for is the focal length. Talk to just about any photographer and he or she will tell you that when it comes to photographing the Moon, a 200mm+ telephoto lens is more or less a requirement due to an effect known as perspective distortion.


One of the consequences of perspective distortion is that the optics of long telephoto lenses have the effect of making distant objects look significantly larger relative to their foreground counterparts. Here's a perfect example. These water bottles are actually the same distance from one another in each of these photos. What changes is:

A) the photographer's distance from the bottles and
B) the focal length of the photographer's lens.


Changing his position relative to the water bottles allows him to keep the field size of the photograph identical between each shot; but by increasing his focal length, he also narrows his angle of view, causing the water bottle in the background to appear larger (and closer) to the bottle in the foreground.

By using a focal length of 600mm, Kotsiopoulos cranks this optical effect into high gear, allowing him to make this rising quarter Moon look more like a looming space station than the natural satellite we all know and love.


You can check out more of Kotsiopoulos' breathtaking photography over on his website.

[Chris Kotsiopoulos via CWL]
Focal length demo via Wikimedia Commons



If I stand in my yard and watch the moon, it looks way smaller than the tree next door, and almost exactly the same size as the tree over on top of that hill. If I take a photo of the moon while it's next to that distant tree, zooming in with the camera lens, and cropping with Photoshop, it will look huge.

This is hardly arcane science.