How Does Aperture Shape Your Photo?
Aperture directly affects the depth of field (DoF) of the photograph, or how much of the photograph is in focus. This is the secret to creating those neat photos of background blur, aka Bokeh.
The lower the f-stop number (f/1.8), the smaller the depth of field meaning that more background blur will occur.
The higher the f-stop number (f/22), the larger the depth of field or more in focus the entire photo will be (focal point and background).
The first important note is that selecting an extreme f-stop setting will affect your shutter speed when you have your camera in aperture priority mode. Ignoring ISO for the moment, the higher the f-stop number will result in less light hitting the sensor. To properly expose the image, the camera will require the shutter to stay open longer (so it gets enough light to "see" the image). The longer the shutter speed, the more likely you will need a tripod to capture a sharp image.
The second note is that the distance between your focal point and the background will affect your photo. In the example image, the flower is about 10 feet or more away from that back hedge. If I can place the orchid directly in front of the hedge, the blur would not be nearly as dramatic.
For this reason, normally photographers say that an aperture of f/2.8 is pretty wide or a “fast” lens. This is because it allows more light to enter the camera so the time the shutter needs to be open is reduced. For hand-held shots, this is critical.
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