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Tomorrow my older brother is graduating college, and I want to be able to capture photos of him getting his diploma so I went to grab my longest lenses, one is 500mm prime and the other is a 70-300mm zoom. As not to look like the awkward photographer, I decided to just take one. But which one?
The 500mm prime has a much sharper image and longer length, but it only opens to f/8 whereas the zoom opens to f/4, two whole stops. I decided to take the 500mm as long as I could get enough light.
The "Sunny 16" rule states that on a day with direct sunlight, set the f-stop to 16 and the shutter speed to reciprocal of the ISO. There is another rule that states, don't ever shoot at a shutter speed less than your focal length.
Knowing all of this I know ill set my f-stop to f/16, my shutter speed to 1/500s and my ISO to 500. With these settings I know I can get a properly exposed shot that's not gonna be blurry and not too noisy (I know photos look good up to 800 ISO and I can get away with 1600 ISO).
But what if I want a lower ISO for a cleaner picture? Well since the minimum f-stop of the less is f/8, I know I can, but how much more?
All I have to do is know stops. Stops are units of exposure which you can translate into any of your three exposure options. To add or subtract a stop from ISO simply double or half it, and the opposite is true for shutter speed. To do the same for f-stop, its 2 stops for each time you double or half it.
So going from f/16 to f/8 is two stops, and knowing ill stay at 1/500s, I can half my ISO twice, giving me 125. Which means ill be able to get a low ISO shot if I want.
Needless to say I packed the 500mm prime and will be taking pictures in the morning.
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