You might be familiar with the “term depth of field”. Generally speaking t-stops are used much more in the filmmaking industry than in the photography world.īesides indicating how much light is coming through a lens an f-stop indicates how blurry the “ out of focus” parts of your image will be. Similarly to f-stops the greater the T-stop number the darker the image. So for example a 100mm lens at f/2 with a light transmittance of 75% will have a T-stop of 2.3. T-stops take in account the percentage of light that comes through a lens and mixes it with the f-stop number. T-stops are a measurement of how much light is actually going through the lens at any given f-stop. So how are you supposed to know how much light is actually going through your lens? T-Stopsįilmmakers in early hollywood answered this question by coming up with T-stops, or transmission stops. Nicer (and more expensive) models typically allow for more light to pass through the lens. Most lenses allow for 60-90% of the light to pass through. Due to the glass elements, it is impossible for a lens to allow for 100% of light to pass through the lens. This is attributable to light transmission through the lens. For example a 50mm f/1.4 lens from Canon will probably let in a different amount of light compared to a 50mm f/1.4 from Sigma. Just because a lens has a similar f-stop doesn’t mean it lets in the same amount of light. The f-stop formula also means telephoto lenses tend to be much wider than comparable standard lenses. The 1.2 is larger than the 1.4 and the 1.4 is larger than the 1.8. Take the the Canon 50mm line, for example. Practically speaking, this means lenses with larger apertures (low f-stop numbers) tend to be physically larger than their small aperture (high f-stop number) counterparts. An f-stop reading is a math equation for the focal length of a lens divided by the diameter of the entrance pupil (or aperture size). While most people think an f-stop is an actual reading of the amount of light that is coming through a lens it is actually far from it. The fractions can get down to the decimal place, buy if you are looking for a comprehensive chart check out this post on Hometown Sevier. For this reason many lenses give users the ability to make half, third, or even quarter steps between f-stops. However, sometimes photographers and filmmakers want a very specific f-stop number that isn’t on this chart. Every lens will give users the ability to step between most of the f-stop numbers listed on this chart. If you move from a higher number (11) to a lower number (8) it is called “ stopping up“. If you move from a lower number (2.8) to a higher number (4) it is called “ stopping down“. Taking your f-stop from a lower number to a higher number decreases the amount of incoming light in half, moving two stops higher decreases incoming light by four and so on. The following chart shows us what f-stop numbers represent full stops: Knowing what numbers represent stops is very important to figuring out how much light is coming into your camera. In photography and video a stop is a step that either doubles the incoming light or cuts the incoming light in half. A lower f-stop number (1.2, 1.4, 1.8, 2) will let in more light compared to a higher f-stop number (8,11,16,22) which doesn’t allow very much light.Īlthough the actual f-stop numbers may seem arbitrary they actually stand for something important. Generally speaking an f-stop will quickly tell you how much light your lens is letting in. If you have any questions please feel free to ask in the comments below! What is an F-Stop?Īn f-stop is the numerical representation of the size of the lens aperture in relation to the focal length. In the following post we will take a look at every aspect of f-stops and how it relates to photography and video. Everything about f-stops run counterintuitive to how one would actually think they work, but have no fear. There is no lens concept more misunderstood than f-stop…and rightfully so. F-stops are crucial to understanding how a camera lens works.
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