Friday, December 7, 2012

Night Turns to Noon

You might want to check out my Blue Moon post before you read this one.

It was late at night. The full moon lay high in the starry sky. Suddenly, everything started getting brighter and brighter, until the moon was as bright as the sun, and everything looked the way it does in the middle of the day - except for the glaring light pollution and the burning stars. Astounded, I pulled out a camera and snapped the photo above, and some others you can see in my Blue Moon post. About an hour later, everything went back to normal.

Does that sound like a true story? Well, it isn't; that night was just like any other. To take the photos, I used a trick that I will explain in this post.

When a digital camera takes a photo, this is what happens: a shutter on the front opens up, and a lens focuses light onto a tiny charge-coupled device (CCD) inside the camera. When the light hits the CCD, a small electric charge becomes present. As more and more light hits that part of the CCD, the charge gets stronger and stronger. Different parts of the CCD have different charges, depending on how much light they get.

After a certain amount of time, called the exposure time, the shutter closes, and the camera converts all those charges on the CCD into an image. The bright parts of the image correspond with stronger charges on the CCD, and vice versa.

Now let's go back to the photo I took in the moonlight. Since it was dark outside, the charge on the CCD would have been very weak, resulting in a dark image. But what if there were a way to make the charge stronger? Then I would have a much brighter image; if things worked well, the image might look as if it were taken during the day.

The trick is simple: change the exposure time. If you set the exposure time higher, then the shutter will stay open longer; the charge on the CCD will be much stronger, and you will have a much brighter image. That's what I did, and the results (not to mention the bragging rights) are certainly worth the time.

Hopefully this post explained some things about cameras and tricks. If you can remember what I said, and can put it into practice, you're well on you're way to becoming an expert photographer. Finally, here's a tip: if you're trying to take a "daylight" photo, don't let any houselights get in the picture. They'll get brighter too, just like everything else.

The video above shows a series of photos taken with different exposure times.
The first photo has the shortest exposure time, and the last one has the longest.

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