Rincon Photography Workshop
Session One: Camera Basics Assignment
F Stop (f/)
To master exposure you must understand the f stops concept – which is really easy!
Think of light as particles called “photons,” because that is what they are called. But for the purposes of this exercise it helps to think of light as particles of sand, that may help. Just don’t get sand next to your lens.
One “stop” is a relative measurement of either:
how much light (how many photons) is allowed to pass through a lens (or funnel if using the sand analogy), controlled by the aperture (neck of the funnel), to the camera sensor
or how long the light is allowed to fall on the sensor as controlled by the speed of the shutter opening and closing in the camera body.
The changes between stops is either a doubling or ½ the amount of light or time.
Lenses - Each setting is a stop. 1, 1.4, 2, 2.8,4, 5.6, 8, 11, 16, 22, 32, 64
Whether you have a point-and-shoot or a 600mm lens, at the same aperture, the amount of light passing through the lens is the same!
Camera - Each f-stops (shutter speed) is: slower < 15, 30, 60, 125, 250, 500, 1000 > faster
In general, if someone is getting good exposures and you ask him/her for their settings (ISO, shutter speed, aperture) you will get the same exposure – even if they are using a 200mm lens on a Canon 5D Mark 3 and you are using a point and shoot with a 50 mm lens.
The basic functions of a lens:
Focus the light reflecting from a subject or scene onto the sensor
Control the amount of light passed to the camera body
Doing both without distorting the image
Lens Terminology and Functions
Aperture: the adjustable opening of the iris (like your eye’s pupil) that controls the amount of light passing through the lens to the camera. Stops are the fixed aperture settings.
“Open” / “Close or stop down:” Terms frequently used to indicate opening the lens to a larger aperture (f/4 to f/2.8); or to close to a smaller aperture (f/4 to /f/16).
The basic functions of the camera body:
Hold the lens
Hold the sensor in the proper position to capture the light coming through the lens
Limit the time light can fall on the sensor (shutter speed)
The rest is gravy
As stated above, shutter speeds control the amount of time light is allowed on the sensor.
Typical shutter speeds – at one stop intervals - are 1, ½, ¼, /1/8, 1/16, 1/30, 60, 125, 250, 500, 1000, 2000, 4000, 8000
ISO/ASA: a measure of the sensor sensitivity to capturing light
In film days, there was one ISO for a roll of film.
Film grain is based on the size of the crystals in the emulsion
Because sensors are electrical devices, we can turn up or down the sensor’s sensitivity to light on a frame-by-frame instance. Similar to turning up the light in a room with a dimmer switch.
Noise is an example of when at higher ISOs the interdependency of physics and electronics collide in unwanted artifacts in our images – initially noticed in the deep shadow areas. Some will still refer to this as grain – but it is not.
For some reason, this topic causes many to have short circuits in their brain, or their eyes cross and it all becomes a blur. Hopefully this simplified approach to one of the most important fundamentals will be less traumatic, and in the end you will have mastered this important concept.
Equivalent exposures are used to achieve a correct exposure with the depth of field you desire, , and a shutter speed which produces sharp or intentionally blurred images.
For example, you want to make a photograph with a large depth of field. Your light meter reading may show 1/500 at f/5.6 for a certain ISO and subject.
To get a f/stop and shutter speed combination which gives a large/ deep depth of field and still gives a correct exposure:
1. Start with 1/500 at F/5.6.
2. a. Go to the next largest f/stop # (next smallest aperture) and go to the next slowest shutter speed to compensate.
b. f/5.6 to f/8 = 1/2 as much light
1/500 to 1/250 = 2x as much light
c. So 1/250 at f/8 is an exposure equivalent to 1/500 at F/5.6 (Equivalent Exposure). But with a slightly greater depth of field due to the smaller aperture.
3. a. Go to the next largest f/stop # (next smallest aperture) and go to the next slowest shutter speed to compensate.
b. f/8 to f/11 = 1/2 as much light
1/250 to 1/125 = 2x as much light
c. So 1/125 at f/11 is an Equivalent Exposure.
4. a. Go to the next largest f/stop # (next smallest aperture) and go to the next slowest shutter speed to compensate.
b. f/11 to f/16 = 1/2 as much light
1/125 to 1/60 = 2x as much light
c. So 1/60 at f/16 is an Equivalent Exposure.
d. Also, it is the slowest shutter speed you can hand hold with a normal lens.
5. a. Go to the next largest f/stop # (next smallest aperture) and go to the next slowest shutter speed to compensate.
b. f/16 to f/22 = 1/2 as much light
1/60 to 1/30 = 2x as much light
c. So 1/30 at f/22 is an Equivalent Exposure.
d. This shutter speed would require a tripod.
Now, make up your own starting points and then change your aperture or shutter speed by several arbitrary stops. Then set the appropriate shutter speed.
Now do this in revers: set an arbitrary shutter speed and calculate the proper F stop.
Get so familiar with this process that you don’t have to think about it, because we will use this basic function all of the time.
Workshop Information and Assignments: http://www.larrypadgett.com/#!rincon/ct7f