1. Light Controls in Photography
How Photography Works

2. Light Controls Photography is dependent on 3 major factors:
Aperture / Fstop
Shutter speed / Exposure
Film or Paper Speed

3. Light Controls in Cameras & Enlargers
You’ll notice that both cameras and the enlargers in the darkroom have these light controls. So, let’s define and explain their functions:

4. Understanding Aperture & Exposure Time
Both cameras and enlargers have a lens where light passes through to expose images.
The size of the hole where light passes through can also be controlled, and this is called the aperture.
They also have a control that determines the amount of time light is exposed to the photographic film or paper for. This is called shutter speed or exposure time.

5. Aperture
Aperture or Fstop- is the size of the opening that lets light in or out. We can equate it to the pupil of your eye and how wide or small your pupil is when it adjusts to different lighting situations. It controls light by how big or small the opening is—a large opening allows a lot of light; a small opening only allows a little light.
Each unit is called a ‘stop’, hence the term Fstop. You can stop up or stop down by changing the Fstop on your camera or enlarger, ie. changing from F5.6 to F4 and vice versa.
Aperture is measured by a specific set of numbers, called ‘stops’:
largest smallest

6. Aperture / Fstop also has a secret-identity— it affects depth of field.
If you pretend that what you are looking at when you look out into the world is several planes of glass all sandwiched together, you can think of depth of field as how many planes of field are in focus at any one time.
The larger the aperture (the smaller the number), the smaller the depth of field—meaning only 1 or 2 planes of glass will be in focus at that Fstop.
The smaller the aperture (the larger the number), the larger the depth of field—meaning a larger depth and area will be in focus as you focus on your subject.
Depth of Field

8. Shutter Speed or Exposure Time
Shutter Speed or Exposure Time- is how long the film or paper is being exposed to light for.
In terms of our relating this to the human eye, it is like blinking your eye—it’s how long you open your eyelids for.
It controls how much light is let in by length of time—the longer the amount of time, the more light is allowed on the exposure.

9. Shutter Speed / Exposure Time
Shutter speed on cameras is measured in fractions of seconds:
longest shortest
We cannot hand-hold any exposure longer than 1/60 without using a tripod; however, because our breathing and heartbeat will move the camera.
Pinhole camera exposures and darkroom exposures are measured in whole seconds, not fractions

10. Motion & Blur with Shutter Speed
Shutter speed also has a secret-identity—it affects motion or blur.
The slower your shutter speed, the more blur (or tracers) you can create in your photograph.
The faster your shutter speed allows you to freeze and capture motion, such as a speeding racecar.
This effect also explains why we must use tripods to capture a clear photo below 1/60, because we cause the blur at that slow of speed just by breathing and being alive.

11. Speed up, stop down; Stop up, slow down.
Shutter Speed and Fstop act inversely upon each other: F t
Basically, each of their setting are measured in ‘stops’, so if you adjust the Fstop by 2 stops,
you have to re-adjust the shutter speed by 2 stops in order for the exposure to stay the
same.
The reason for this is that if you adjust the size of the hole (the aperture) that lets in light,
and you let in more light, then you will have to change the length of time that hole is open
for, the exposure time, because they both affect how much light hits your film or paper.
A good rule of thumb for making sure your exposure stays the same while you change
things like your depth of field, or adjust the shutter to avoid blur is:
Speed up, stop down; Stop up, slow down.

12. Film & Paper Speed The common range of film ASA or ISO are:
Film and Paper Speed- refers to how quickly the film or paper absorbs light. It is called the ISO or ASA of the paper or film. These numbers are logical and progress in speed/absorption as they get larger. The bigger the number, the faster the film reacts to light.
The common range of film ASA or ISO are:
( )
Photo-paper has an ISO of about 10.

13. Grain Quality
The other difference between film speed is the grain quality— the lower the speed, the finer the grain of the film and final image. This is why portraits are usually shot on 100-speed film. Speed of film is also important in capturing images in low-light situations or of quickly-moving subjects.

14. The Difference in Grain Quality in different ISO films

15. Review of Light Controls