Recently, it become apparent that some students have trouble understanding the relationship between Aperture, Shutter Speed and ISO and how they effect exposure for a given photograph. First let’s define each:
Aperture or f Stop – is the size of the opening in the lens that allows light to hit the camera’s sensor. f stop is expressed as a fraction. An f/3.5 lets in a larger amount of light than an f/16. Aperture also affects the Depth of Field (DOF). Depth of Field is an area in front of the subject and behind the subject that is in focus. More about DOF in a later blog, except to say that larger f stops give smaller/narrower DOFs.
Shutter Speed – is the length of time the shutter is open allowing light to come through the lens to the camera’s sensor. If you are taking photos handheld, my recommendation is to never use a Shutter Speed less that 1/50 second, often displayed as 50 on your camera’s LCD and/or in the view finder.
ISO – is the sensitivity at which the sensor operates. The higher the ISO number used, the greater the sensitivity, and the better the camera’s ability to shoot in low-light conditions. However, higher values may give the photo a grainy appearance. I recommend not using Auto ISO. From my observations of students’ photos, the quality of the photos suffers because Auto ISO often allows for too slow a Shutter Speed and results in a blurred photo when the camera is hand-held.
When shooting in Automatic Mode the camera controls all three, Aperture, Shutter Speed, and ISO. Automatic does not necessarily give a good photo. I’m an advocate of taking control of the camera. Once you understand how your camera works, you will take better photos.
Below is a student’s photo taken in Automatic Mode. This photo is one of the first pictures taken with a new camera. The photo is dark and blurred. Note the Shutter Speed of 1/20 second.
Aperture, Shutter Speed and ISO are all tied together to get a photo with the correct exposure. In Automatic Mode the camera makes all the choices. When you shoot in any mode other than Automatic, such as Aperture or Shutter Speed you have more control over the resulting photo.
In manual mode, you have total control of all three which gives you the greatest amount of control, but also the opportunity for failure. I recommend new students start with Aperture Mode and use Shutter Speed Mode when you want to stop the motion of the subject.
Where do you start?
When you use your camera in Aperture Mode, denoted as an A or Av on your camera’s mode dial, you control the size of the lens opening and the camera sets the Shutter Speed. Remember you want the minimum Shutter Speed to be 1/50 or faster for hand-held photos.
In Shutter Speed Mode, denoted as S or Tv, you are selecting the Shutter Speed and the camera controls the Aperture.
First set your ISO. What setting do you use? Are you outside on a sunny or partially cloudy day? Try ISO 100-200. If you are inside a building with good lighting ISO 200 or 400 could be a good place to start. In early morning or evening around sunrise or sundown you may have to use something like ISO 800 or higher.
In a concert hall you may have set the ISO much higher depending on the lighting. The concert photo to the left ISO 2500 was used.
In Aperture Mode, remember that the camera determines the speed for the ISO and Aperture you set. Let’s look at the Photos below. Do you see any differences in the photos?
Hopefully your answer is no. In Aperture mode, the camera compensates for the different values in Aperture f/5.6 and f/22 by a corresponding change in the time the shutter is open. You see that for the smaller aperture f/22 the time was 1/125, much longer than the 1/2000 for f/5.6. Let’s see what happens when we change to ISO 800, but still use the same Apertures as before f/5.6 and f/22.
All four photos look about the same. Why? Because the camera compensates for changes in Aperture and ISO to always yield a good exposure.
At higher ISO, the sensor would have been more sensitive to light and would require a Shutter Speed faster than 1/8000, or an Aperture smaller than f/22 both of which are beyond the capability of the camera and lens used in the photos above.
What would happen if you chose to operate the camera in manual mode, which would allow changing Aperture, Shutter Speed and ISO independently? How would the photo change if the Shutter Speed was 1/125 with an Aperture of f/5.6?
Would it brighter or darker?
Scroll down to see the answer!
The answer is “Brighter”. Did you get the answer correct? The slower speed 1/125 lets in more light than 1/350, so the photo would be over-exposed, i.e. Brighter.
I hope this helps you better understand the relationship between Aperture, Shutter Speed and ISO.
The link below from PetaPixel.com should help with your further understanding of Aperture, Shutter Speed and ISO.
Please contact me if you have any questions.
photos available for purchase at FineArt America
© Tom Wiggins Photography 2015-2023
I am no longer sure where you’re getting your information, however great topic. I needs to spend a while learning much more or figuring out more. Thanks for magnificent information I was looking for this information for my mission.
Alex:
Thank you for your comment. Understanding Aperture. Shutter Speed and ISO are fundamental to getting away from using your camera in Automatic Mode. I stress these concepts in my Introduction to Digital Photography class, along with the use of Aperture and Speed priority modes and choosing the correct ISO for the lighting conditions you experience.
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