Photography pt. 2 – Depth of Field
Well, I couldn't fit all the photos I wanted to into one article… so I made a second one to showcase some photos that help to explain the whole Depth of Field thing and how it is affected both by the aperture, the focal length of the lens, and the distance between the camera and the subject.
In the series of photos below I kept my camera in the same position relative to the lineup of shoes and just changed lenses and camera settings to demonstrate how depth of field works. The camera setting changes are noted in the captions of each photo, and you'll notice that each photo in a series represents a change of one stop. I close the aperture from f2.8 to f4 and slow the shutter speed from 1/320th to 1/160th to compensate for the difference in light.
In the series of photos shot with the 35mm, notice how much more quickly the shoes all come into focus when the aperture changes. This is because it is a wider lens than the 70, and thus has a deeper depth of field. With the 70mm it takes much longer for shoes in the back to become more recognizable. These differences would have be magnified even more if I was closer to the shoes (and less magnified if I was farther from them).
I've copied the text about Depth of Field from the first article below.
Aperture. A lens’s aperture is much like the pupil of your eye. The smaller the hole, the less light that will hit the film. The size of an aperture is referred to as an f-number or f-stop. You will frequently see labels like f1.4, f5.6, and f16 — these are all different f-stops. Out of these three apertures, f1.4 would allow the most light, f16 the least.
A second, and very, very important feature of a lens’s aperture is depth of field. The depth of field of a picture is the amount of the frame in focus or sharp. An f-stop of 1.4 has an extremely shallow depth of field, meaning only what you focus on will be sharp, the rest of the frame will be soft and out of focus. A picture taken at f16 will have a much deeper depth of field, meaning what you focus on, as well as much of the foreground and background will appear sharp. Depth of field is also affected by what lens you choose and how far you are away from the subject. The shorter (more wide angle) the focal length (zoom) of the lens, the greater the depth of field. The greater the distance from your camera to the subject, the greater the depth of field, as well. So if you were really close to your subject with a long lens and shooting at f2.8, you would have a very, very shallow depth of field. But if you were far away from your subject with a wide lens and shooting at f16, you would have a very, very deep depth of field. For example pictures demonstrating how depth of field can be controlled, scroll to the end of the gallery in this article.
*Terminology note: Aperture and f-stops can be very confusing at first and hard to understand the terminology. Here is an overview to help.
On early cameras the aperture was adjusted by individual metal “stop” plates that had holes of different diameters. The term “stop” is still used to refer to aperture size, and a lens is said to be “stopped down” when the size of the aperture is decreased. The standardized, full stop of series numbers on the f-stop scale runs as follows: f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64. Many lenses and cameras have the option to change f-stops in full stops, half stops and third stops (e.g. f2.8, f3.2, f3.5, f4). The largest of these, f/1, allows the most light. Each f-stop after that admits half the light of the previous one. A lens with a larger aperture is said to be “faster.” A lens that opens up to f1.4 is said to be faster than one that can only open up to f2.8. On many lenses there is a “floating” aperture. For example, a common lens in the consumer market with a floating aperture is the 75-300mm f4.5-5.6. This means that at 75mm the lens can open up to f4.5, but if zoomed out to 300mm, the lens can only open up to f5.6 — losing two thirds stops of light.