Photography used to be a very expensive hobby when it relied on the use of photosensitive film. Today, virtually everyone can get their hands on a camera of some sort and capture images. The rise of digital photography represented a major shift in the art and science of making images, but the footprint of film is still very much visible in today's practices.

If you're trying to be a savvy photographer today, it's necessary to understand how it used to work when it was all about film and chemistry.

How photosensitive film works...

Photography means the art and science of drawing (or painting) light

imagePhotography began as and remains to be a way in which people captured light to create images. Photosensitive film was loaded into a camera body and quickly exposed to light, in order to create a chemical reaction on the film. Because of the nature of photosensitive chemistry, the spots that received the most light would be darkest. This created an opposite image on the film, which is called a negative.

Exposed film would be processed in complete darkness with chemicals that slowly developed and set the negatives. Once rinsed with developer, stop bath, fixer, and water in a light-tight container, negatives could then see the light of day.

These negatives were then taken to a darkroom where photosensitive paper could be exposed to the images through an enlarger. Since amber light doesn't affect the photo paper, it could be used to see around the darkroom. Once exposed to light through the negative, the photo paper could be developed, placed in a stop bath, fixed, rinsed, and finally dried to create the physical photograph everyone knows as the main event.


That's how film was and still is (though less so) processed from shutter click to paper image.

The shift to digital...

DSLR (or digital single lens reflex) cameras are based on the 35mm film cameras of yore. 35mm refers to the width of the negative, and this was the standard size amongst the range of options. Medium and large format cameras were more popular in the early days of photography, though much bulkier and less versitile.

A popular user of the large format camera you may well know was Ansel Adams. He would lug a large format camera into the American national parks in order to take perfectly exposured, completely focused images of nature. He was also a wiz at composition...but that's another talk for another time.


Ansel had a perfect grasp on the concept of exposure: how the light hits the film. In digital photography, the film has been replaced by a sensor, which reads the light in the same manner but stores it as a positive image in a digital capacity. Big sensors perform better in low light situations, provide greater control over depth of field, minimize digital noise, and create higher resolution images. The Canon 5D Mark II is a common example of a full-sensor camera body that gets as close to 35mm photography as we get these days.

Though we're no longer dealing with photosensitive chemicals or negatives, cameras still create an exposure in the same way. Here's a good video that explains how aperture, shutter speed, and ISO combine to calculate the proper exposure for a photographic image.

As this video explains, there are three components of exposure: aperture, shutter speed, and ISO.

Aperture: the doorway for light

imageLight enters your camera body and reaches the film/sensor through the doorway of the aperture. It is the physical, circular opening that controls how much light is let into the camera. Though it might seem counter-intuitive, the wider the opening, the lower the number. For example, an f-stop (the name for each aperture setting) of 2.8 is a wide circle, whereas an f-stop of 22 is a very small hole. Each f-stop is either half or double the f-stop next to it, which helps in determining your shutter speed.

The f-stop not only restricts the amount of light in but affects the depth of field of your image. If you have a low f-stop, you create a shallow depth of field. This means that only one focal length away from the camera is in focus. The rest is blurred out to some extent. Conversely, if you have a high f-stop, the entire image will be in focus. This relates to optics, and I can't explain any further than that. Consult your local scientist for more details on how a camera makes the magic it does :)

Shutter speed: the duration of light

Depending on how wide you open the door, you need to adjust the speed at which you do so. Shutter speed refers to the amount of time the film/sensor is exposed to light. Most of our images take a fraction of a second–e.g. 1/125, which usually shows us as 125 on the camera body. Anything faster than 1/60th of a second usually freezes human motion, but 1/30 and slower start showing evidence of movement in the subject or in the photographer. A camera can sense your heartbeat at 1/30 and blur your image because of it! If you're trying to capture a splash, sports, or something in fast motion, you might need the highest shutter speed your camera can handle.

ISO: how sensitive to light

imageFilm used to have varying levels of photosensitivity, meaning some worked like magic in low light while others needed a bright and sunny day. They made international standards with which to categorize film and its photosensitivity. This is called ISO. If your digital camera is set to Auto ISO, the camera will determine what ISO to set the camera to for each individual lighting situation. If it's set at a certain ISO, the light meter within the camera will base its settings of aperture and shutter speed to work with that setting.

Just as aperture affects the depth of field and shutter speed affects the motion captured, ISO affects the quality of the image. A low ISO of 100 or 200 creates the highest quality image, whereas an ISO of 1600 or higher will be visibly grainy (or noisy in digital terms). Keep that in mind!


Here's a writing prompt that will allow you to develop your understanding of the true capacities of the photo medium and your use of it: Is what the camera sees and produces reality?

Now that you know how your camera functions and how to measure the proper exposure, maybe you're wondering what the next steps are, such as taking a photo and knowing what to do with it once taken. We will cover that when light painting continues with the practice.