The Basics of F-Stops and Exposure Settings


Happy Monday everyone! Last month, we began a new series of photography tutorials that will cover the basics of photography. We started with a lesson on  focal length. This week, we continue the series with a look at f-stops and exposure settings.  If you have, or are interested in purchasing, a DSLR camera then these tutorials are a stepping stone on how to begin using your camera's manual mode. By learning the basic features of your camera, and how all these features work together, you can begin to take control of your picture taking instead of letting the camera dictate how your pictures will be exposed. Let's get started!

Aperture and f-stops

When you take a picture you allow a certain amount of light through the lens, focusing it onto the image sensor. The aperture sits inside the lens and controls how much light passes through the lens and onto the sensor.   A large aperture lets through very much light and a small aperture lets in very little light.  One of the most important parts of photography is knowing how the aperture affects the photograph.  Aperture affects the amount of light you let in, the depth of field, the lens speed, the sharpness and vignetting.

The amount of light you let in is measured in what we camera  folks call "stops".   F- Stops are mathematical numbers that express the diameter of the aperture and are a relative measure of lightness.  They are a VERY  important part of understanding how the aperture and exposure work.  Once I figured out the f-stops and how they correlated to light...the rest just seemed to click together!

F-stops have a common notation and on each camera it may be a little different. For instance, my Canon Xti shows the f-stop as "ƒ/5.6" but my mother's older Canon shows her f-stop as "5.6".  Although both indicate the same amount of  light your camera is letting in, they are a little different in their appearance. There is a standard set of  f-stops that are used in photography. They are:

ƒ/1.4   2   2.8   4   5.6   8   11    16   22  32

In the above f-stops, the largest aperture is 1.4. It will let in the most light while the smallest aperture of  32 will let in the least amount of light.  Now remember what I said about understanding this concept? This is what I mean. The smaller the number=the larger amount of light. So if you are shooting outside and it is dusk, you will want your f-stop to be 1.4 or 2. However, if it is bright sun outside, shooting at a higher f-stop like 11 will let less light in and will keep your photos from being overexposed.  When someone says "close", "reduce" or "step down" the aperture, they mean to increase the f-number.

I could go on and on about f-stop and exposure, but all you really need to know is that if you decrease the f-stop by one full-stop (meaning you go from a ƒ/8 to ƒ/5.6) then the amount of light that passes through the sensor will double. If you increase the f-stop by one full-stop (going from a  ƒ/8 to ƒ/11) only half the amount of light will reach the sensor. It is easier, however,  if you think about it using this formula:

higher  f-stop = smaller aperture = less light

lower f-stop = larger aperture = more light

The amount of light you record is controlled by the camera's exposure settings: aperture, shutter speed and sensitivity. This means that you can open the aperture by a stop or decrease the shutter speed by a stop or even increase the sensitivity by a stop and each one of those steps will all have the same effect; they will double the brightness of your photo. Making the decision of which setting you use BEFORE you shoot, especially when it comes to the shutter speed and aperture settings will have other aesthetic effects that affect how your picture looks, so knowing how these work together can really make or break your photo.

For instance, aperture also affects the look of the photo, specifically the depth of field.  At narrow apertures (like f11)  the whole scene will be in focus, whereas at wide apertures(f2.8) only the bit of the scene that you focus on will be on focus. So, if you decide that you want the background to be blurry then you know that you will have to change your f-stop number to 2.8. Once you decide that number, THEN you will change the settings for your shutter speed and ISO. These three settings work TOGETHER to create a well shot photo.

The photo below, of my daughter Allison, was taken using an f-stop of 2.5.  Shooting at this wide aperture allows my daughter to be the focus if this photo while the background is out of focus and less distracting.  The lower the aperture the blurrier the background will be.  Notice how she appears to stand out away from the background.


This photo, of my oldest daughter, Rachael, was shot using an f-stop of f8.  Shooting at narrow apertures will allow the whole scene to be in focus. The higher the aperture, the more of the scene will be in focus.  In this photo, Rachael appears to blend in with her surroundings.



Shutter speed

Now let's take a look at shutter speed. The shutter is what controls how long the image sensor is exposed to the light. The longer the shutter is open the more light can be captured by the sensor. I like to think of it like the shutters on your windows at home. If you open the shutters and keep them opened for  a long period of time, you let more light into the room.  Shutter speed is used when determining how you want your photo to appear. A fast shutter speed, or longer exposure to light,  will result in “freezing” a moving object. For instance, in the picture below, I used a  shutter speed of 1250 when shooting my daughter playing softball. Even though she has thrown the ball, it is "frozen" in the air meaning that you can not see any movement.


Settings: f5   ISO 200    1/1250s

Thinking back to the shutters in your house again, if you got up one morning, opened the shutters, realized it was too much light and shut them, you still let in light, but just a small amount of it.  A slow shutter speed, or less exposure to light, will let you capture the motion of a moving object.  In the photo below, The f-stop and ISO settings are the same as the photo above, however, the shutter speed is now set to 500.  The result is a blurry bat and hands. The motion blur depicts the movement of the subject.


Settings: f5   ISO 200    1/500s

Neither setting is considered the 'correct' way to photograph. It is really just up to you, the photographer, and how you want the photo to feel. I like to shoot both ways. It is always cool to me to "freeze" a subject, but there are times when I want the movement to show, like in the photo above.  I LOVE that you can see the muscles in her arms tighten to pull the bat around and the movement in the bat and hands allow you, the viewer, to imagine the motion.

Finally, there is a common scale of stops for the shutter speeds just like there are for aperture:

1/1000s    1/500s    1/250s     1/125s     1/60s    1/30s    1/15s    1/8s    1/4s    1/2s    1s

The shutter speed is often on a 1/3 scale, giving you two steps in between every full-stop. For example between 1/60s and 1/125s you will find 1/80s and 1/100s.  It can be rather confusing, but the thing to remember is that the lower the stop (1/2s) the less light is let in and the blurrier the motion will be. The higher the stop (1/1000s) the more light is let in and the more "frozen" the motion is.

This week, your homework is to play with your aperture and shutter speed settings. Begin by taking photos at your lowest aperture settings  and then move to the highest aperture setting. Note the difference in the depth of field when you look at the two photos.  Next, practice shooting a moving subject and changing  your shutter speed settings.  When I was learning my settings, I took my child to the park, put her on the swing  and shot away! While you are shooting, take note of how the brightness of your photo is affected when you change the settings. Is it over or underexposed? Can you change the brightness level by changing the f-stop or the shutter speed? Work the two settings TOGETHER to get the effect you want on your photo. For example, if you want to "freeze" the motion, set your shutter speed first, THEN choose an aperture that will let in enough light. If you want your subject to be in focus and the background to be blurry, choose your f-stop first and then set your shutter speed to allow for the proper light. Learn to use these settings together and next week we will add one more setting to the mix!

I can not tell you enough how important it is to practice. You will never become comfortable with shooting in manual if you do not understand how each of these settings controls the outcome of your photo.

Next month, we will learn about ISO,or sensitivity settings, as well as learn about metering. Learning each of these important aspects of photography start you on your way to becoming the photographer you always wanted to be!

Have a great week and don't forget to PRACTICE!!!