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F stop numbers4/8/2023 Exposure is measured in exposure value (EV), also called stops. The agreed standards for shutter speed are 1/1000 s, 1/500 s, 1/250 s, 1/125 s, 1/60 s, 1/30 s, 1/15 s, 1/8 s, 1/4 s, 1/2 s, 1 s.Ĭorrelation Between Shutter Speed and ApertureĪperture and shutter speed together determine exposure. Standard ways of representing aperture are in sequence (f/2.8, f/4, f/5.6, f/8, f/11, f/16, etc.). In other words, the f-number is the focal length divided by the "effective" aperture diameter. It is a representation of the diameter of the aperture stop in terms of the focal length of the lens. The actual size of the aperture depends upon the focal length of the lens.Īperture is also called f-number (sometimes called focal ratio, f-ratio, f-stop, or relative aperture). Each aperture has half the light gathering area of the previous one. increasing f-numbers, in one-stop increments. Units for specifying shutter speed and apertureĭiagram of decreasing apertures, i.e. a crisp picture of a football player in mid air. A higher shutter speed allows clear images that are great for capturing specific moments in time e.g. Images taken with a lower shutter speed are blurred and invoke a visual sense of movement. The impact of shutter speed is most prominent when photographing moving objects. So in effect, it helps the aperture restrict the amount of light that is allowed to reach the object. The shutter speed controls the length of time that a camera's shutter remains open. So the subject matter may be at a greater distance from the plane of focus and still appear in focus in the photograph. So all objects at varying distances from the view finder will be in equal focus. the distance range over which objects appear acceptably sharp in the picture) is larger. If the aperture (diameter of the aperture stop) is small, the depth of field (i.e. The degree of the sensor's exposure to light determines the brightness of the picture. The aperture and shutter speed together control the amount of light reaching the image sensor (or film) of a camera. both systems result from the basic division f/a.A shot of a jet of water from a hose fast shutter speed to capture a crisp image of moving water drops. While the current 'standard' is for the f/2 series numbers awhile back many european cameras came with their own system with stop numbers like 6.3,9,13,18. Once upon a time people used round holes of various sizes on a strip or disc to "STOP" the amount of light reaching the emulsion and that is the origin of the word I believe. It may be common practice to call video lens by t-stops but in the history of film and video this is a recent practice and all my lenses were f/stop labled. However "words mean what I mean them to mean" as one famous wordsmith put it. I also suggest one should use / and not. Some may think in 'pure' whole numbers but that ignores the potential for f/2.8 or f/4.5 or f/6.3 to list just three common examples. Whatever the number it is it is the result of a mathematical calculation of dividing the the focal length of the lens by the aperture so it is possible to have any number and decimal places. I've seen some Canon lenses as well, for APS-C and full-frame video camera, but don't know if they are purpose designed video lenses or repurposed still lenses. Optically, they are idential but the features plus gearing for follow focus are included. Samyang has come out with lenses for both still and video. The "t" stand for transmission and unlike camera lenses, where the f-stop is purely based on the geometry of the lens aperture, the t-stop also accounts for light loss within the lens. The video lenses don't call them f-stops, but rather t-stops. As the distinction between still and video cameras is blurring, you can certainly get video lenses for Canon and Nikon mounts. Those lenses do not have click stops and do have infinitely variable iris settings. As to you defination of "f-number" as "the infinate possible apertures sizes bewteen standard f-stops", is wrong in my opinion, as the aperture size is not varible inbetween standard stops.A small bit of trivia for you Allan - if you are using a lens designed for video, the statement is true.
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