This morning as I was going to work, the full moon was in the sky and very bright. I could clearly see the dark spots on it. I got my phone out (after stopping) and thought to get a picture, but no matter how I tried to focus the camera, it couldn’t see the moon as anything but a bright ball of light, like looking into a flashlight. Why was it so difficult for my phone to capture this image that my eye could see so clearly?
In: Technology
When we use a DSLR/mirrorless we either need to set the exposure manually or set it to ‘spot’ and focus the center of the frame on the moon. By default most smartphone cameras will meter using something called ‘evaluative’, which is to say it will try and see the entire scene and meter based on something called a histogram. This is typically very reliable, but it fails when you have a extreme highlights (the light of the sun reflecting off the moon) contrasted against a super dark shadow – like the night sky. What you get is something called ‘blown highlights’. Digital sensors prefer under-exposure to over-exposure, when you overwhelm a digital sensor with light, all the data basically gets confused. Film was the opposite, under-exposure meant you didn’t have data at all, it could normally go a full ‘stop’ overexposed and still give you a useable image.
If you ever hear a photographer say “expose for the highlights’, this phenomenon is what they are talking about. With photographing the moon, you **must** expose for the highlights. Say I am photographing a couple of people sitting at a table and behind them is a slider door and it is broad daylight, if I expose for the highlights I want to see the background sky nice and blue. Doing this will make the faces nearly black, which is why I use a flashgun to light up the faces and expose for the background. It is why you see photographers use their flash when there seems to be plenty of available light.
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