Yesterday we discussed relatively in-depth about ISO, and how best to use it to your advantage. If you are just joining us feel free to read all about it here.
Today's topic is F-Stop. It is referred to in many different ways, and on its own, can tell us a lot about style, performance, and even equipment itself.
F-Stop and Focal Distance
F-Stop, when concerning what is called 'Depth of Field' adjusts the focal distance of your lens. At a low F-Stop number of F/1.8-F/2.8 your focal plane is very narrow, this would be good when shooting objects, or close-ups of a single subject.
(Click image to see full size)
As your F-Stop increases to F/2.8 - about F/5.6 the focal plane widens allowing multiple objects to remain in focus.
F-Stop Settings approaching F/16, F/22, and F/32 (depending on the optical length of the lens the minimum/maximum aperture can vary) allow very wide focal planes ideal for landscape shots or a long exposure shot of a starry sky.
F-Stop and 'Speed': Aperture
F-Stop can also refer to how 'wide' open the aperture of your lens is (one thing that has not significantly changed from film to digital, if at all). Given a lens with a maximum aperture (the lowest F-Stop number) for F/1.8, the lens would be considered to be 'wide' or 'fully' open, allowing the most light possible in the shortest amount of time (fastest shutter speed).
If you have ever heard the term 'fast lens' or someone asks you the question of how 'fast' your lens is, etc., this too would tie back into F-Stop and Aperture. A lens' speed is determined by its maximum aperture. For example, given a lens with a long optical length, it is typical for the minimum Aperture/F-Stop to be as high as F/5.6 when zoomed in; this is considered a slow lens. To contrast, a faster lens ideal for indoor or low light usage with a comparable zoom range could be a 70-200mm (shorter than a 70-300) with a minimum F-Stop of F/2.8; this is considered a fast lens.
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