{"id":468,"date":"2018-05-07T10:23:41","date_gmt":"2018-05-07T15:23:41","guid":{"rendered":"https:\/\/luxumbraque.com\/-\/?p=468"},"modified":"2018-05-15T09:22:06","modified_gmt":"2018-05-15T14:22:06","slug":"not-all-apertures-with-the-same-f-stop-are-the-same-size","status":"publish","type":"post","link":"https:\/\/luxumbraque.com\/-\/2018\/05\/07\/not-all-apertures-with-the-same-f-stop-are-the-same-size\/","title":{"rendered":"Not All Apertures with the Same F-Stop are the Same Size"},"content":{"rendered":"

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Not All Apertures with the Same F-stop are the Same Size<\/figcaption><\/figure>Not all apertures with the same f-stop are the same size, so it’s a mistake to think that an f-stop tells you directly how big an aperture is. In fact, f\/8 on one lens might even be bigger than f\/2.8 on another. Here’s why.<\/p>\n

The f-stop is relative to the focal length of a lens. It’s the ratio<\/i> of a lens’s focal length to the size of the aperture letting in light. So f\/8 on a 50mm lens means the aperture is 50mm\/8 or 6.25mm in diameter. But on a 100mm lens, that same f\/8 aperture is 100mm\/8 or 12.5mm in diameter.<\/p>\n

Because the area of a circle quadruples as its diameter doubles, f\/8 on a 100mm lens lets through four times as much light as f\/8 on a 50mm lens.<\/p>\n

But longer lenses let in less light to start with. That 100mm lens only lets in one quarter the light of a 50mm lens. A 400mm lens lets in only 1\/64th the light of a 50mm, but its f\/8 is 64 times bigger. And so on. In other words, the f-stop tells you how much total light is getting through.*<\/a><\/sup><\/p>\n

This is why the f-stop system is so useful. If f\/16 and 125\/sec at ISO 100 gives you a good exposure in sunlight with a 50mm lens, the same settings will give you a good exposure in sunlight with any other lens.<\/p>\n

But there’s a big catch.<\/p>\n

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