Understanding Your Digital Camera
Lesson 4 - how your camera and lens work together

We take so much for granted these days... our work, our homes, and our health. Have you ever thought what it would be like not to have the use of your eyes? It gives us a feeling of empathy for the unsighted. Well, image what your camera would be like without a lens. It's about the same concept. We need sight as much as a camera needs to see. Read on in these next few lessons about how the lens works and the magic behind the image.

Since the camera and lens, film or digital, are fashioned after the human eye, it seems fitting that we also understand how the eye works. The cornea could be considered the front glass element or filter. We know the cornea acts as a protection device for debris and objects entering the eye. The iris might be the aperture control to limit light coming in. As the ambient light gets brighter, the iris constricts and cuts down the light volume. And the retina just might be the light sensor to understand what we look at... all controlled by the brain or camera computer. Neat, huh?

In the illustration, at right, look at the different elements and their jobs:

1. Lens- multiple pieces of ground glass forming a group working together to give a precise view to the film or light sensor
   
   
2. Reflex Mirror- giving the user the ability to look through the lens via the mirror and prism. The reflex refers to the mirror's ability to flip up out of the way just prior to the shutter opening for the exposure. The mirror returns to its original position immediately after the exposure is complete. In a point and shoot type camera, a viewfinder window is used instead of the mirror. Another option is sometimes using the LCD to help the user frame their picture.
   
   
3. Film or light sensor- where the image is captured. Film receives the image through the lens and behind the shutter; known as a "latent image." Digital cameras use a light sensor which receives the image like the film process and stores the pixel data in flash memory storage cards.
   
   
4. Film Backing Plate- only employed on film cameras. This plate helped keep the film flat to aid in precise focusing of the lens image across the film surface.
   
   
5. Prism Fresnel- this thin piece of glass has alignment features used to help the user accurately center horizons within the image. It is also where the image is projected onto by the mirror. Since it is not optically clear, but slightly matte, it "stops" the image projection so the user can see this through the prism.
   
   
6. Prism Lens Element- used to focus the image on the Fresnel into the prism.
   
   
7. Prism- a configuration of mirrors to display the image from the lens to the viewfinder so the user can see through the lens.
   
   
8. Prism Eyepiece Lens- the lens element that works in conjunction with the prism lens element to give precise image clarity. In some cameras, this is adjustable for varied eyesight ranges.

the human eye

side view of single lens reflex or SLR

So, as you can discern from this information, the human body was an inspiration to photographic inventors through the years.

The lens is as important to the camera as our eyes are to us. In the next two lessons, we will present information on wide angle and telephoto lenses. Now that we know how the eye and normal lens works, it's also useful to know how wide and tele lens help our pictures become more interesting... read on!