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Which Aperture Should I Use?
 In my role as a photography tutor, “What aperture should I use?” is one of the most frequent questions I am asked. I have come to the conclusion that it lies at the root of a bigger query, “how does my camera work?” Camera manuals are all well and good but, unless you want to find out what a button does or where to find a specific thing in a menu, they don’t really tell you what to do when physically taking a photograph. In this article I am going to explore both questions and, hopefully, provide some direction when choosing the correct aperture at the correct time. First of all, what is an aperture? The aperture hasn’t really got anything to do with your camera, it all happens within the lens. It is basically the hole, which lets light in. You can change the size of the hole by setting an ‘F’ value, the smaller the number, the wider the hole. Many people refer to these numbers as ‘F Stops’ which can be confusing because stops are not solely attributed to apertures and many modern cameras have values, which don’t equate to whole stops! I tend to simply call them ‘F Numbers’ or ‘F Values’ to avoid confusion. Right now we’ve sorted that one, what is an ‘F Number?’ On common, mass-market lenses ‘F Numbers’ tend to range from F1.4 to F22, although some lenses can open wider than others and some can close down narrower. In between these values are a series of stops, (a photographic measurement of light), which, confusingly increase by of the square route of two each time. Don’t worry; you don’t have to be a mathematician to work it out. All you have to remember is that the smaller the number the smaller the hole. What does this all do? Apertures are one of the main factors affecting depth of field. This is the amount of your photograph is in focus, also known as the ‘plane of focus.’ As a rule of thumb, the wider your aperture, the shallower your ‘plane of focus’ or ‘depth of field’ will be. However, a common misconception is that if you have your aperture set at F1.8 then whatever you photograph will have a blurred background. This can be the case, however, it also depends on how close you are to your subject. You could take a close up shot at F11 and still get background blur. You’re probably now thinking, well, that’s all well and good but I still don’t know which one to select and when. Which aperture do I use? Well, we have neatly come full circle to the original question we first asked. At least you should now have a greater understanding of what apertures are all about. This means we can make an educated selection. When selecting your aperture I would ask yourself the following questions… 1. What is my desired depth of field? a. If you want to go for a shallow depth of field select a smaller number. b. If you are close to your subject F5.6 or F4 might be sufficient, if you are further away you may need to go wider. c. If you require a long depth of select F8 or F11 for the best results. 2. How much light do I need? a. If your shutter speed is struggling you may need a wider aperture to let more light in. If you are taking a wide-angle shot stop down, (a colloquial term for widening the aperture), to F5.6 and let the ISO take the rest of the strain. If you are taking a close up and want a blurred background, the same rule could apply. While you’re here, what else is there to know about apertures? Without wanting to get too technical, apertures are all about light diffraction or how much your lens has to bend light to make it form as a point of focus on your camera’s sensor or film. Many people are told to get a super-long depth of field you should select the narrowest aperture possible. This however is a load of rubbish. In reality narrow apertures, like F22, can have the effect of softening the image rather than sharpening it. This is due to the way the small hole affects the light’s pathway through your lens. For the best results select an aperture between F5.6 and F11 for landscape shots and between F2.8 and F5.6 for close ups. Remember it also depends on how far you are from your subject to the effect it has on the depth of field.
©YORKSHIRE PHOTO WALKS 2017 • TOM MARSH PHOTOGRAPHY
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