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How Digital Cameras Work: Lenses (part 2)

See the first part here

Lenses are one of the most important elements of a camera. Previously I covered the general idea of how a lens works and the different parts that make up lens. In this article I will cover how a lens and the aperture actually work.

Light Refraction
When you look through the viewfinder on you camera you can see your lens in action. As you turn or manipulate the lens while looking through the viewfinder you can see the refraction of light in the lens in real time. The reason you are able to see this is because of how the lens manipulates the light. To best explain how a lens works it is best to consider a very simple lens.

Laser passing through each lens in the lens assembly. Image by yellowcloud.

As light enters the end of the lens it is manipulated by the first lens. This lens is typically a convex lens that refracts the light inward. This lens will make the light that enters invert on itself, essentially inverting the image. The light that passes through this first lens is refracted to pass through the aperture in the lens. After it has passed through the aperture, the light passes through another lens. This lens is a concave lens that refracts the light outwards. This will make the initial image larger. The light refracted through this lens is what is used to expose the image sensor (or film).

Essentially this is how the light refraction in a lens works. Light is refracted in a lens in different ways depending on what type of lens you are using. For example telephoto lens refract light in a vastly different way than wide angle lenses. The refraction in each of these different lenses is based on the lens setup of each. In most lenses you use you will rarely find a simple concave or convex lens setup typically the lenses inside your camera lens are special versions of concave and convex lenses. While the type of lens will determine the lens array, another factor in how the internal lenses are designed is color aberration. Color aberration is a major concern in lens development as it can effect the entire color and look of an image. I may cover this more in another article.

Aperture Apparatus

Aperture inside a lens. Image by nayukim

Aperture is usually a confusing concept for most beginner photographers. Aperture in photography refers to the actual diameter of the aperture device, in the form of f-stops. The larger the f-stop number the smaller the opening. This concept usually confuses people just starting out in photography. The easiest way to remember this is by replacing the f in the f stops with a 1, converting it into a fraction (f/8 and f/11 become 1/8 and 1/11).

Aperture assembly. Image by Richard Masoner / Cyclelicious

The reason the opening of this aperture is important is because it determines the collimation (density) of the light reaching the image sensor (or film). A wider aperture allows more of the admitted light to expose the image sensor, allowing burring from the lack of collimation. A narrower aperture only admits light rays that are closer together, creating a sharper image. Aperture in photography also affects your depth of field.

[via Photography Tips » Photography Tips & Tutorials]

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