As you get more comfortable with the camera and the settings, you can start to take creative control by better understanding how the camera makes its decisions and where you might have to take back some of the decision making.
KEY
TAKE-AWAYS
Stopping up / down
E/V compensation
What does it mean to
STOP UP
and
STOP DOWN
?
Before we start, let's first define a stop. It's simple enough, but since you'll be hear this terminology often you should understand what's being said. A stop is an increment up or down that either doubles or halves the amount of light being allowed into the camera. This can be achieved using the shutter speed, the aperture or the ISO. Let's look at an example:
Say you are shooting with the following settings:
Aperture f/5.6
Shutter speed 1/10
ISO 400
The following 4 photos demonstrate stopping down 3 consecutive stops, using shutter speed:
Set A Photo 1
Aperture f/5.6
Shutter speed 1/10
ISO 400
Set A Photo 2
Aperture f/5.6
Shutter speed 1/20
ISO 400
Set A Photo 3
Aperture f/5.6
Shutter speed 1/40
ISO 400
Set A Photo 4
Aperture f/5.6
Shutter speed 1/80
ISO 400
Each step represents a halving of the light used to create the image because the time allowed to let light into the camera is cut in half, while the other settings stay the same. Simple.
You can make a change to any single setting and that will either double or halve the amount of light reaching the sensor. Starting with the same settings we left off with, consider the following:
Set B Photo 1
Aperture f/5.6
Shutter speed 1/80
ISO 400
Set B Photo 2
Aperture f/5.6
Shutter speed 1/80
ISO 800
Set B Photo 3
Aperture f/5.6
Shutter speed 1/80
ISO 1600
Set B Photo 4
Aperture f/5.6
Shutter speed 1/80
ISO 3200
Look at the resulting exposure and notice that we are back where we started. The settings that produced the first photo of set A, and the settings that produced the last photo in set B result in a photo with the same exposure. I could post another set of photos that show the same result by changing the aperture up and down. I won't, but I could.
You can make a change to any single setting and that will either double or halve the amount of light reaching the sensor. Opening your aperture (to a smaller number) along the f-scale will mean more light will reach the sensor. The same would be true if you doubled the ISO from 200 to 400. The camera is twice as sensitive, so the resulting image is twice as bright. This is referred to as stopping up.
If you stop down, then you're doing the opposite. Taking the ISO from 200 to 100, or changing the shutter from 1/100 to 1/200, for example will halve the amount of light reaching the sensor. ISO and shutter speed are fairly easy to understand because if you're any good at math, and you understand the anatomy of a camera, you should be able to visualize what is happening when you open the shutter for twice as long or half as long. Also, the numbers make it easy. ISO works in numbers which are easy to calculate. 100, 200, 400, 800, etc. They keep doubling. Same with fractions. 1/50, 1/100, 1/200. It's easy to extrapolate using these numbers. Aperture, however, is a little tricky.
Aperture uses a confusing numbering system. If you remember, aperture is measured in f-stops and those are 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. I have briefly explained this system in class, but the short version is that this numbering system refers to a ratio defined by the distance between the lens and the aperture and the size of the aperture in mm. It doesn't matter. What matters is that by moving between them, either up or down the scale, you can stop up or stop down, just like we discussed above. The confusing part is that because this numbering system isn't incremental, f/2 and f/4 don't have the same doubling relationship, because those two aperture settings are separated by f/2.8.​
When you go from f/2 to f/2.8, that's two times the light.​
Then, when you go from f/2.8 to f/4, that's two times the light, again. As a result, f/2 lets in 4x more light than f/4. Confusing? Yeah, a little. Sorry. That's just the way it is.
And there's more.
As you get more comfortable with the camera, you'll start to want to take more creative control. Understanding stops can help you ensure the correct exposure, while allowing for varying depths of field, or allowing the capture of a fast moving subject with a fast shutter speed by stopping up your camera and compensating for the difference. It's a bit to take in, but the basics are that you have more than one path to create a properly exposed photo, which means you can take better advantage of the camera's capabilities.
MEDIA
Hopefully there will be a video here soon. This will be part of a class lesson where the finer details of this are explained.
READINGS
In the meantime, if you want more information, you can read the Internet.
QUESTIONS
Which are functionally the same?
A. iso 400, ss 1/50, f/5.6
B. iso 1600, ss 1/25, f/16
C. iso 800, ss 1/100, f/16
Rollover for answer >
I found this comment on a photography website where a user explained the concept really clearly. Here's what they write:
A 'stop' is a doubling (2x) or a halving (0.5x) of the amount of light and a stop is a fundamental photography concept.
A stop change in exposure can also apply to shutter speed and ISO.
Since exposure is a triad of adjustments (shutter speed, ISO, lens aperture) you can change 1, 2 or all 3 of the triad settings.
If you want 1 more stop of exposure (brighter) you can adjust just one of the 3 by 1 more stop.
Or, you can change 2 of the 3 by 1/2 more stop each for a net gain of 1 stop of exposure.
Or, you can adjust all 3 by 1/3 more stop for a net gain of 1 stop of exposure.
You can also change the triad of settings and have no change in the exposure.
If you change 1 of the 3 settings by 1 stop more exposure and change a 2nd setting by 1 stop less exposure the net change is zero.
Suppose you subtracted a stop of shutter speed to help stop subject motion, you could add a stop of lens aperture to keep the exposure the same. However, adding a stop of aperture will also effect the total DoF by a small amount. So, if you don't want the DoF to change you would add a stop of ISO instead, However, adding a stop of ISO will increase by some amount the image noise in the photo.
Note: DSLR cameras are set by default to adjust the exposure settings in 1/3 stop increments.
Most DSLR cameras let you change that to 1/2 stop or 1 stop increments.
However, the advantage of 1/3 stop step increments is more precise control of exposure.
EXPOSURE VALUE COMPENSATION
Earlier in the course, we learned about the control triangle. The camera looks at your scene, decides if it's bright enough or dark enough and make changes to the settings to allow for a correct exposure. But, sometimes what the camera wants and what you want are not the same thing.
Exposure value compensation allows you to quickly brighten or darken a photo in increments equal to 1/3 of a stop.
In the simplest terms, this means allowing the camera to permit the scene to be a little brighter or a little darker than the sensor thinks it should be. This is useful in and of itself, but here are some specific examples of when you might use exposure value compensation.
Maybe you're shooting a photo of the sunset. The sky is vibrant red, orange and purple, but when you look at your photo it's dull and washed out. What's more, the ground in the foreground is a medium grey instead of black. In this particular example, you care about the vibrant colours of the sky, not the foreground. But the camera sees those blacks and decides that the scene is too dark. It sets a higher ISO or a larger aperture, allowing in more light. The blacks are no longer too dark and the camera has done its job, saving your photo. In reality, because you don't care about the details in the shadow, the camera has ruined the shot. Here's where exposure compensation can help. By setting the EV compensation to -1 or -2, you are forcing the camera to darken the photo more than it normally would. This turns those greys into jet black, allowing the colours of the sky to remain vibrant.
Another example is shooting photos where the scene is meant to be very bright, like snow. Your camera will look at the scene and decide that there is too much white in the scene and use the settings to darken the entire scene. Those whites become murky and grey. That's not what you want. You want the scene to be bright white - after all, it's snow. Setting the exposure value to +2 (or perhaps more) will tell the camera to set the scene 2 stops brighter than it normally would, allowing the whites to be white.