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How we Measure the Aperture

Just as we measure weight in lbs or kgs, we also need a unit for the aperture--so, whatever camera you use, you'll know exactly how bright or dark the image will be when you change the aperture size. The unit for aperture is called f-stop. We write it as a fraction with the letter f on the top and a number at the bottom (example: f/4). Whoever came up with this didn't care for simplicity, but all we care about is the number. Just keep in mind the number is a denominator, so a larger number means a smaller aperture. Lenses come with a fixed set of f-numbers that you can set (f/2.8, f/4, f/5.6, up to f/22). So, for instance, if you are in a dark place, you need a large aperture (to let more light in), so choose a small f-number.