{"id":76282,"date":"2025-08-27T08:16:40","date_gmt":"2025-08-27T07:16:40","guid":{"rendered":"https:\/\/phillipreeve.net\/blog\/?p=76282"},"modified":"2025-08-27T16:25:13","modified_gmt":"2025-08-27T15:25:13","slug":"understanding-f-numbers-and-light-transmission","status":"publish","type":"post","link":"https:\/\/phillipreeve.net\/blog\/understanding-f-numbers-and-light-transmission\/","title":{"rendered":"Understanding F-Numbers and Light Transmission"},"content":{"rendered":"

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Introduction<\/h2>\n

When comparing camera lenses, one of the most commonly discussed features is how “fast” a lens is\u2014usually expressed in terms of f-numbers. But what do those numbers actually mean, and how precise are the differences we talk about, like \u201chalf a stop\u201d or \u201ctwo-thirds of a stop\u201d?
In this article, we\u2019ll unpack how f-numbers relate to light transmission, explore why the system isn\u2019t always as exact as it seems, and show you how to calculate these differences for yourself\u2014or simply reference our handy table at the end.<\/p>\n

<\/p>\n

Background<\/h2>\n

When we include alternative lens options in a review, we often highlight how much faster or slower they are compared to the lens being tested. For example, we might note that Lens A is half a stop faster, or that Lens B is one and a half stops slower.<\/p>\n

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Nikon’s older lenses (Ai\/Ai-s, E-series) are marked and clicked at full-stops only, except if their max aperture falls between two full stops<\/figcaption><\/figure>\n

However, these figures are often only approximations. This is because lens and camera manufacturers have adopted different conventions over time, and the way aperture values are displayed doesn\u2019t always reflect the true mathematical differences in light transmission.<\/p>\n

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Some lenses, e.g. Carl Zeiss Pancolar, are marked at full stops only, except if their max apertures fall between two full-stops, like the Nikon lenses, but they have half-a-stop clicks<\/figcaption><\/figure>\n

Most modern digital cameras show f-stops in one-third stop increments. Some older or mechanically simpler lenses use half-stop clicks on the aperture ring and some other only full stops. Both systems are convenient but not always precise.<\/p>\n

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Modern lenses either have one-third of a stop clicks or the aperture can be set by the camera at one-third of a stop<\/figcaption><\/figure>\n

Let\u2019s look at an example. Say you have a lens with half-stop increments and a maximum aperture of f\/1.7. The next step on the ring might be f\/2, implying that f\/1.7 to f\/2 is treated as half a stop. But what if the same lens used one-third stop steps instead\u2014would f\/1.8 appear between f\/1.7 and f\/2? And would that mean each step is now a third of a stop, which makes the same f\/1.7 to f\/2\u00a0 to be treated as 2\/3 stop?<\/p>\n