Another aperture question?

Question by kirr45: Another aperture question?
I asked a question related to aperture and how it affects “blurriness”. I had trouble understanding the concept that depending on the aperture, a picture can become blurred. The reason I don’t understand this is because isn’t this the job of the focus on the lens? Doesn’t the focus on the lens allow you to adjust focus on where you want it. For example if you want to do a portrait and blur the background, wouldn’t you just adjust the focus? Why would you need aperture to blur it?

Best answer:

Answer by fhotoace
You do not understand the relationship between the aperture and depth of field. Wide open produces a shallow depth of field, something portrait photographers use all the time. A lens that is stopped down to say f/16, will provide a larger depth of field. However there is a forth component. The length of the lens. A wide angle lens provides more depth of field at any aperture than a long lens shooting at the same aperture.

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2 Responses to Another aperture question?

  1. gatewaycityca says:

    Yeah, I answered your other question. I don’t know how else to explain it. The aperture determines how much light comes in to the camera, AND the depth of field. Yes, the lens focuses the image, but the “depth of field” determines how much will be in focus in front and behind the subject. The depth of field means the “leeway” that you will have, how much you can be off on the distance and still have an acceptably sharp image. If you use a small aperture, like f/11 or f/16, you will have a long depth of field and you can be off a little bit on the distance and still have an acceptable picture. But with a wide aperture, like f/8 or f/5.6, you will have a very shallow depth of field, and so you need to be a lot more precise with the focusing.

    Think of the depth of field as the “margin” or “range” of what will be in focus.

    This is why a wide aperture will cause a blurry background, because it gives a very shallow depth of field, and will have a very short range. Beyond that range of focus, the picture will be blurry.

    Conversely, if you want to have a sharp background (like for taking landscape photos), then you need to have a long depth of field and you will need to use a small aperture, like f/11 or f/16.

  2. Slighly Amused says:

    The aperture determines the amount of focus around the focal point of the camera or where it is focused at. An aperture of say 1.8 will not add any focus beyond the point of focus of the camera whereas an aperture of f16 will bring the focus of the camera so what is in front and behind the ACTUAL POINT OF FOCUS will be more in focus.

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