The first part is the size of the lens, which generally allows you to see farther. Now with the HD camera’s offered today you can still see the clarity behind, but think of it as a “zoom” feature without pixilation of the image or actually having to physically “zoom” in.

As you can see, as your lens gets higher, you get a closer shot of the image with consistent clarity of the original show. As you get closer though, your horizontal angle of view becomes much smaller.

Angles:

Often when purchasing a camera you will want to know the viewing angle which is directly impacted by the mm of the lens you select. The higher the mm of the lens, the less of a “Horizontal” angle you see. Think of this like a large window in front of you. As you walk close to it, you see less of the windows outer frame, but more of what is inside the window. You can see a much farther distance, but you see less of the original area.

This Chart will help explain Horizontal angle of view:

The positioning of the camera can impact your Horizontal line of view. If you were to place a 6mm camera on the corner of a building watching an intersection, you would see less of the surrounding sidewalks than if you put the camera mid-building.

Aperture:

The Aperture is how much light the lens actually allows into the picture. This image will help you see the difference in the numbers:

This can have a large affect on how the image in the background can be displayed. As you can see with the next image, having a higher Aperture can definitely help you see what is happening in the background more clearly.