The moon is smaller than you think: big moons and big lenses

I just listened to a SALT talk (the little brother of the TED talk) by Jim Richardson, a photographer for National Geographic. In the introduction Stewart Brand said something that is somehow strangely non-obvious: Journalists can write prose from a distance, but a photographer always has to be there to get the shot. Richardson joked that many people, on looking at his portfolio, ask the same question: “Did you really go to all these places?” His well-rehearsed reply: “Well, yes. That’s how it works.”

The National Geographic website has a series called Extreme Photo of the Week, by which they mean breathtaking pictures of people doing really stupid, dangerous things. The kinds of pictures that make otherwise sane people say to themselves “My life is so dull. I should really take up poisonous kayak cliff diving.” I’m as much of a sucker for them as the next guy. Just see if you don’t spend the next fifteen minutes annoying the other person in the room: “Holy crap! Look at this guy! That’s insane! I know I said the last one was insane too, but this one is really insane. Come look. Seriously.”

Since it’s National Geographic, you get this extra benefit of the photographer explaining how they got the shot. So I was pleased to come across this picture of a crazy person dancing on a rope in front of a great big moon. Now the thing that interests me here is actually the big moon and not the crazy person. There are a great many irresponsible moon photos in this world, pictures where a moon has been pasted into implausible or impossible positions, sizes, and phases. And you rarely get the story of how the moon ended up so big (assuming it’s not a total fake job). Ever notice how if you try to take picture of the moon it’s always a teeny-tiny thing off in the corner? The angular diameter of a full moon is around a half a degree, a small fraction of the human field of view. You will never ever seen a scene like this with your naked eye, partly because your eye is incapable of making a moon look this big, and partly because their just aren’t enough crazy people dancing on mountaintop ropes to go around. And the photographer spells it out for you, which is the part I like. He was 1.2 miles away from his human subject, and using a hell of a lens (800mm f/5.6 lens with a 2X doubler).

That’s how you make a giant moon.