Sometimes folks have asked why we describe the aperture value in “f\/stops” and it seems like weird nomenclature that may not make sense. Actually it makes total sense once you know what it means. <\/p>\n\n\n\n
Let’s say you want to know the size of an aperture. We answer with some f\/stop number. But exactly how big IS the aperture diameter in millimeters? The f\/stop is the answer. “f” is the “focal length”. The aperture size is the focal length divided by the number.<\/p>\n\n\n\n
The aperture size (in millimeters) for f\/4 is the focal length divided by 4. Let’s say you have a 100mm lens at f\/4 What is the actual size of the aperture in millimeters? 100mm\/4 = 25mm. How about a 100mm lens at f\/2. What is its actual aperture diameter? 100mm\/2 =50 mm. <\/p>\n\n\n\n
That also explains why longer telephoto lenses that go to lower f\/stop values are larger and more expensive. It’s because it takes a larger diameter glass to implement an f\/2.8 lens vs an f\/4 or f\/5.6 lens. If you have a 400mm lens at f\/2.8, its aperture diameter would have to be 142.9mm which is quite large (and expensive)! A 50mm lens at f\/2.8 would only need to be 17.9mm in diameter.<\/p>\n\n\n\n
Now, you know! \ud83d\ude42<\/p>\n","protected":false},"excerpt":{"rendered":"