Aperture and focusing

Put simply it is a hole, which can be made bigger or smaller. A bigger aperture (smaller f/number) allows more light to enter when the shutter opens. A smaller aperture (larger f/number) allows less light to enter when the shutter is open.

No, it is the opposite. You should Google/Read about "Depth of Field", which is a measure of how deep the area is that will be acceptably in focus. A large aperture (small number) will have only a narrow area in front/behind the point of focus. A small aperture (large number) will have a much wider area which is acceptably in focus.

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Dan
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I love my girlfriend, my dog and my canon 5DIII - even though none of them ever do what I tell them
I am learning photo graphee - see the results at www.danmarchant.com