Principles of operation of a photo camera
- how does a photo camera work

Here I describe the basic principles of a photo camera. Every camera consists of four technical elements - as we will see now:

• The Objective lens, it concentrates the light and projects it onto the image plane,
• The Aperture, which regulates how strongly the light influences the process,
• The Shutter, that regulates how long it is exposed to light and
• The Image sensor (the image plane, for example landscape or a person, that gets hit by the light).

The objective:

The front part of the camera is the objective. Written on the objective lens are normaly the following two specifications: the maximum capacity of light intensity (luminosity) and the focal length. Through the lens (or to be more precise lens system) light enters the camera. In the objective is the aperture with its lamination. The aperture lamination allows, that the aperture can be adjusted bigger or smaller and thus regulates the amount of light entering the camera. More about objectives in the chapter about the objective.

Aperture

The aperture is inside the objective. With the aperture ring you can easily adjust the size of the focal aperture, viz. controlling the amount of entering light. Modern cameras don/´t have a aperture ring anymore instead a motors adjust the focal aperture.

The bigger the focal aperture the more light enters the camera. For that the aperture lamination changes. Therefore the f-number or lens stop is directly linked with the "hole size".

In the operation mode P (programmed auto) the camera decides by itself, which focal aperture seems reasonable.

The f-number can also be adjusted manually (using AV = Aperture Value, in some manuals named as aperture priority

The f-numbers are standardized and the f-number 5,6 of an objective is identical with the f-number 5,6 on another objective.

So, if the objective has a maximum of for example 1,4, then this number of 1,4 is the maximum aperture. Using this means that the maximum amount of light enters the camera through the objective. While adjusting the camera a photographer always works with the maximum aperture, also termed working aperture (in the German literature). The aperture automatically stays fully opened and lets the maximum amount of light entering the camera. This is very helpful to evaluate the over mirrors projected image seen on the viewfinder.

To activate the lamination in the aperture you need the depth preview button. After pressing this button the lamination of the aperture become visible when you adjust the f-number. Only in the maximum aperture mode is the aperture lamination hidden, because the aperture is opened to its maximum. The higher the f-number, the more the lamination closes. A number of 2,0 means, that only half the light enters the camera compared to the number of 1,4. Adjusting the camera to the f-number 2,8 means that only half the light falls into the camera compared to the f-number 2,0. If you set the f-number to 4,0 and take a look at the objective you can clearly see that there is only a small opening through which light can enter the camera. These f-number jumps can be confusing and are in-depth explained in the chapter about the aperture.

The camera shutter:

In the back part of the camera is a mirror, a shutter (most common are central shutter or a leaf shutter) and an image sensor. The mirror projects the picture onto the small viewing window on the back of the camera and the viewfinder. On old cameras there is also, behind the mechanical shutter, a glass panel for controlling the image section. When triggering, the shutter opens and lets light enter the camera and fall onto the image plane for the time the user has set. Then the shutter closes again. The exposure time (also called shutter speed) can be varied, viz. the speed, with which the shutter closes again and with that the duration that light can enter the camera.

Some cameras allow "turning on the mirror lock-up". This is very useful, when vibration is deadly to the photo, viz. when taking night shots. When activating the function mirror lock-up the camera the mirror flips away after the inital pressing of the trigger and because of that there is no vibration-induced motion blur, when taking the actual photo with the second triggering. The second triggering opens the shutter (curtain) and exposes the image sensor to the entering light. As soon as the exposure time is over the shutter (curtain) closes again and the mirror flings back.

There are several more connections between f-number and exposure time and there are a lot of helpful tipps for an optimal picture with the perfect exposure, which I will describe in the following chapters.

The image sensor (image plane)

The image sensor uses the entering light and converts it in digital values. For that the image sensor delivers different qualities, which generally distinguishes themselves by size (the bigger the better). The chapter „the image sensor of a digital camera“ explains the important mechanisms of it and key terms around it like resolution.

Principles of operation of a photo camera
- how does a photo camera work

Here I describe the basic principles of a photo camera. Every camera consists of four technical elements - as we will see now:

• The Objective lens, it concentrates the light and projects it onto the image plane,
• The Aperture, which regulates how strongly the light influences the process,
• The Shutter, that regulates how long it is exposed to light and
• The Image sensor (the image plane, for example landscape or a person, that gets hit by the light).

The objective:

The front part of the camera is the objective . On the objective lens are normaly the following two specifications: the maximum capacity of light intensity (luminosity) and the focal length. Through the lens (or to be more precise lens system) light enters the camera. In the objective is the aperture with its lamination. The aperture lamination allows, that the aperture can be adjusted bigger or smaller and thus regulates the amount of light entering the camera. More about objectives in the chapter about the objective.

Aperture

The aperture is inside the objective. With the aperture ring you can easily adjust the size of the focal aperture, viz. controlling the amount of entering light. Modern cameras don´t have a aperture ring anymore instead a motors adjust the focal aperture.

The bigger the focal aperture the more light enters the camera. For that the aperture lamination changes. Therefore the f-number or lens stop is directly linked with the "hole size".

In the operation mode P (programmed auto) the camera decides by itself, which focal aperture seems reasonable.

The f-number can also be adjusted manually (using AV = Aperture Value, in some manuals named as aperture priority

The f-numbers are standardized and the f-number 5,6 of an objective is identical with the f-number 5,6 on another objective.

So, if the objective has a maximum of for example 1,4, then this number of 1,4 is the maximum aperture. Using this means that the maximum amount of light enters the camera through the objective. While adjusting the camera a photographer always works with the maximum aperture, also termed working aperture (in the German literature). The aperture automatically stays fully opened and lets the maximum amount of light entering the camera. This is very helpful to evaluate the over mirrors projected image seen on the viewing window.

To activate the lamination in the aperture you need the depth preview button. After pressing this button the lamination of the aperture become visible when you adjust the f-number. Only in the maximum aperture mode is the aperture lamination hidden, because the aperture is opened to its maximum. The higher the f-number, the more the lamination closes. A number of 2,0 means, that only half the light enters the camera copare to the number of 1,4. Adjusting the camera to the f-number 2,8 means that only half the light falls into the camera compared to the f-number 2,0. If you set the f-number to 4,0 and take a look at the objective you can clearly see that there is only a small opening through which light can enter the camera. These f-number jumps can be confusing and are in-depth explained in the chapter about the aperture.

The camera shutter:

In the back part of the camera is a mirror, a shutter (most common are central shutter or central shutter) and an image sensor. The mirror projects the picture onto the small viewing window on the back of the camera. On old cameras there is also, behind the mechanical shutter, a glass panel for controlling the image section. When triggering the shutter opens and lets light enter the camera and fall onto the image plane for the time the user has given. Then the shutter closes again. The exposure time (also called shutter speed) can be varied, viz. the speed, with which the shutter closes again and with that the duration, light enters the camera.

Some cameras allow "turning on the mirror lock-up". This is very useful, when vibration is deadly to the photo, viz. when taking night shots. When activating the function mirror lock-up the camera the mirror flips away after the inital pressing of the trigger and because of that there is no vibration-induced motion blur, when taking the actual photo with the second triggering. The second triggering opens the shutter (curtain) and exposes the image sensor to the entering light. As soon as the exposure time is over the shutter (curtain) closes again and the mirror flings back.

There are several more connections between f-number and exposure time and there are a lot of helpful tipps for an optimal picture with the perfect exposure, which I will reveal in the following chapters.

The image sensor (image plane)

The image sensor uses the entering light and converts it in digital values. For that the image sensor delivers differen qualities, which generally distinguishes themselves by size (the bigger the better). The chapter „the image sensor of a digital camera“ explains the important mechanisms of it and key terms around it like resolution.

Autor: Axel Pratzner