Day +52: Teaching aperture

Before we get to this week’s lesson, it was a beautiful afternoon, so we went for a walk down at Shepherd’s Bay, which is near Meadowbank. There is a long walkway that, in one direction, leads to a park, and in the other, to sporting fields. Here are 2 images I captured during the walk:

20150614-walk-005 20150614-walk-006


Today, I’m launching the first in a series of lessons for keen photographers, covering all aspects of photography. Today, we talk about aperture, or more specifically, depth of field. The term (often shortened to “DOF”), describes how much depth in the picture is in focus. This is, to a large extent, determined by the aperture (although other factors, such as focal length- ie. how long the lens is, also have some say in DOF). The bigger the number of the “f-stop”, the more depth of the picture is in focus. Depending on how “fast” the lens in your camera is (the faster the lens, the more light is allowed to reach the camera’s sensor), you might achieve an f-stop of 2.8, or sometimes even lower, like 1.4 or 1.2. These are in the domain of significantly more expensive lenses, whilst your basic lens might have a minimum aperture of 3.5-4.0. The lower the f-stop, the less depth is in focus, and this is great for situations where you want to isolate a subject (eg. portraits). When done properly, the subject is in sharp focus, and the background is blurry (this blurriness is called “bokeh”, and this is why people pay so much money for faster lenses).

However, there are situations where you do not want a shallow DOF. One such example is scenery / landscapes. Here you want most (if not all) of your image to be sharp, and hence you “stop down” the lens- ie. use a smaller aperture (a bigger f-stop, such as 8-16, or even greater). The photo below illustrates this fact beautifully. Initially, it might seem that this is a wonderful image of autumn leaves:


But the photo was shot with an aperture of 2.5, using a 35mm lens. As a small image, you can get away with it, but the minute you enlarge it, you can clearly see the flaw:


The tree trunk is completely out of focus! In reality the trunk was no more than a metre behind the leaves that were nearest to the camera, but at 2.5, it was rendered out of focus. This is why I always advocate shooting with cameras that allow you to set the aperture manually- most point & shoots allow this, but if not, you can use the “scene” mode, rather than the “portrait” mode.

Well, that’s it for the first lesson. I hope you enjoyed reading it, and I look forward to presenting a new lesson in the not-too-distant future.