Aperture is directly related to shutter speed. Remember the bathtub analogy? We want to fill up the tub. If we use a large hose (aperture), the time we leave the tap open will be short. If we use a thin hose, the time to fill it will be longer.
For each shutter speed, there is a "correct" aperture setting to achieve good exposure. This is also true the other way. For each aperture setting, there is a "correct" shutter speed.
If you choose Tv mode (time value), you are in control of the shutter speed and the camera chooses the aperture that will expose the image correctly.
If you choose Av mode (aperture value), you are in control of the aperture, and the camera chooses the shutter speed that will let in the correct amount of light to expose the image correctly.
So, why is aperture important? Shouldn't we just focus on shutter speed? Excellent question, I'm glad you asked.
Depth of field
After exposure, depth of field is the second most fundamental aspect of photography. We use depth of field to control what is in focus and what isn't in focus.
The aperture, or opening in the lens, controls the depth of field in a picture. Depth of field is a technical term to describe how much of the image is in focus. Images with a wide depth of field have everything from very near to very far in perfect focus. Images with a narrow depth of field have only a narrow strip of the image in focus, with everything else blurred.
A wide depth of field is desirable especially in landscape photography, architectural images, and for any type of documenting (police work, etc). A narrow depth of field is perfect for portraits, closeups of plants and flowers, and any image with a distracting background.
A large aperture creates a narrow depth of field and a small aperture creates a wide depth of field.
A large aperture goes together with a fast shutter speed.
A small aperture goes together with a slow (long) shutter speed.
Controlling Depth of Field
Three factors can be adjusted to control depth of field - aperture, focal length, and distance from the subject.
For a narrow depth of field you can use a large aperture, a long focal length (zoom lens), or get closer to your subject. Or use these techniques in combination.
For a wide depth of field, use a small aperture, a short focal length (wide-angle lens), or move further away from your subject.
One tip to remember is that the zone of sharpness extends 1/3 of the way in front of your subject and 2/3 of the way behind them. So, when trying to decide where to focus in a scene to achieve maximum depth of field, choose a point 1/3 of the way into the scene and focus there with manual focus. This is referred to as the "hyperfocal distance" in photography.
Let's move on to some technical stuff now.
Shutter speed is easy, because it's measured in seconds, which we all know about. Aperture is tricky because it's measured in F-stops.
Common f-stop numbers:
f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/44, f/64
Notice that the 1 and 1.4 numbers are taking turns doubling.
Here's the 1 doubling sequence - 1, 2, 4, 8, 16, 32, 64
Here's the 1.4 doubling sequence - 1.4, 2.8, 5.6, 11, 22, 44
This sequence represents the varying hole size in a lens (the aperture) through which light passes
Each aperture allows twice as much or half as much light to pass as the preceding or following aperture.
Large f-stop = small opening
Small f-stop = large opening
It's may be easier for you to think of them as fractions.
½ is bigger than 1/22.
Opening up means going to a larger aperture (f/8 to f/4) doubling the amount of light entering the camera.
Stopping down means going to a smaller aperture (f/2 to f/4) halving the amount of light
- f/8 lets in twice as much light as f/11
- f/8 lets in 4X as much light as f/16
- f/11 lets in half as much light as f/8
- f/11 lets in 1/4 as much light as f/5.6
- f/11 lets in 1/8 as much light as f/4
- f/4 is 2 stops more open than f/8
- f/16 is 1 stop more closed than f/11
- f/1.4 is 3 stops more open than f/4
Other f-stop numbers exist, but you only need to memorize full stops. Did I say memorize? Yes, I did! You can't call yourself a real photographer if you don't know your f-stops.
Reciprosity (let's review)
- Shutter speeds and aperture work together to control the amount of light hitting the sensor.
- They are a pair
- If you adjust the shutter speed one way you must also adjust the aperture reciprocally
- Open up the aperture & speed up the shutter speed
- Stop down the aperture & slow down the shutter speed
- Double one scale and halve the other, you end up with the same amount of exposure
- Analogy: Work 10 hours at $2 an hour or 2 hours at $10 an hour. Either way you end up with $20.
- The total amount of light hitting the sensor is the same
- f/11 & 1/15 = f/8 & 1/30 = f/5.6 & 1/60 = f/4 & 1/125 = f/16 & 1/8 = f/22 & ¼ =f/32 & ½
- Count the number of stops you change in either aperture or shutter speed and change the same number of stops for the other setting
- Increase one and decrease the other
What's the difference?
- Aperture controls depth of field, the portion of the photo that is in focus.
- A large aperture gives a narrow depth of field (blurry background)
- A small aperture gives a wide depth of field (clear foreground and background)
- Always start by asking yourself, is Motion Control(MC) or Depth of Field (DOF) more Important?
· Landscapes = DOF
· Sports = MC
· Posed Portraits = DOF
· Nature Photography = DOF & MC
· Photojournalism = DOF & MC
· Architecture = DOF
Once a photographer knows which factor they feel is most important, they set that factor first.
For example, a photographer wishes to take a photograph of a meadow with mountains in the background. The photographer wants a large depth of field so aperture is the most important factor in that case. The photographer then sets a small aperture(large depth of field) and allows the camera to control shutter speed. If the resulting shutter speed is slower than 1/60th of a second the photographer uses a tripod.
Now that you understand the important relationship between aperture and shutter speed, we can introduce the third element in exposure, ISO (also known as ASA or film speed).