F-stop, Depth of Field
and other mysteries...
F-stop can be a great mystery to the beginning photographer, but once it is mastered, it can be a great step toward taking better photos. Many point-and-shoot cameras, and all DSLRs have the capacity to control the f-stop. On many cameras, this setting is referred to as the "A" or "Av" setting.
What is f-stop?
F-stop refers directly to how wide the aperture in your camera is. The aperture is a small hole in your camera that lets the light in. It looks like what you see in the very center of this photo:
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In order to change how big or small the aperture is, you change the f-stop number. You can change this number in your camera's manual mode or aperture priority mode (the M or Av mode, respectively).
With me so far? Now hang in there.
F-stop and Aperture
A
low f-stop number will create a
large aperture.
A
high f-stop number will create a
small aperture.
Confusing, I know. But keep reading!
A small aperture will let in a smaller amount of light, because after all, it's a smaller hole! A large aperture will let in a large amount of light. Therefore, in low light settings, it is often advantageous to have a large aperture, and let in more light. Does a large aperture correspond with a high or low f-stop???
You got it... low!
A smaller f-stop number (the number you can control) will cause your aperture to be large... letting in more light.
F-stop and Depth of Field
Light is not the only reason to control your f-stop! Your f-stop will also affect your
depth of field. Your depth of field is how much of your image is in focus. Think about looking down the length of a ruler. Your depth of field will be how much of that ruler is in focus, or readable... 1 inch? 2 inches? All 12 inches?
So how do we control the depth of field, and what does this have to do with f-stop? Well, a
low f-stop corresponds to a
shallow depth of field. This means that only a sliver of your photo will be in focus. For instance, the foreground may be in focus but the background will be blurry. Many people like this effect for up close shots of faces and flowers.
A large, or
deep depth of field can be achieved by having a
high f-stop. Many cameras have a typical f-stop range from f/5.6 up into the teens and 20s with the standard kit lens. If you upgrade your lens, you will find that many quality lenses can have an f-stop as low as f/1.8 (or slightly less). This is wonderful for achieving great focus in the foreground and a beautiful blurry background (especially helpful for Etsy or ebay product photos!).
An F-stop Example: The Book
This first picture of a page in a book has a very low f-stop, f/1.8. That means that it's letting in a good amount of light, and the depth of field is very shallow. Notice how only a few lines of text are readable.
Now, don't allow yourself to think that the items closest to you have to be in focus... the depth of field does not have anything to do with how far away your subject is. It only determines the amount of your subject that will be in focus. I could have easily shown the top few lines of text in focus rather than the bottom few.
Now this photo was taken with a slightly higher f-stop, f/5.00. Notice how more lines of text are readable.
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Now this last photo was taken with an f-stop of f/8.00. Because it was dark outside, I was not able to take a picture with a higher f-stop than f/8.00. Remember, the higher your f-stop goes, the less light the camera lets in. This means that your surroundings need to be brighter if you plan to be holding the camera by hand (less light = slower shutter speed = camera shake... to be continued later).
Make sense? Good! Now let's test you.
I have five questions below, and if you so choose, post your answers in the comments section. I will post the answers later this week! (You may want to read to the end... hint hint.)
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1. Does the image above have a high f-stop or low f-stop?
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2. Does the image above have a shallow depth of field or a deep depth of field?
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3. Does the camera that took image above have a large or small aperture at the time the photo was taken?
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4. Did the camera taking the above photo let in a lot of light or a small amount of light when taking the picture (ignoring other variables besides f-stop)?
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5. Does the image above have a low f-stop or high f-stop?
If you chose to participate, just answer in the comment section below! I will do my best to correct any wrong answers via email if possible so that you can learn from any mistakes. Don't be shy, give a whirl!
Answers are posted here.
As an added bonus, I will randomly choose one person who has answered all the questions correctly, and they will receive a small prize (nothing huge, but something fun!). So if you don't have your email address linked to your blogger, be sure to leave it in the comment so I can contact you if you win!
*Edit: Contest is closed, but feel free to continue to comment!*
What to do if you can't control your f-stop
I also wanted to mention for those of you who do not have a camera that can control the f-stop, that you can recreate these settings with a bit of work! First of all, I would assume that most cameras have a landscape setting. This setting is to force your camera to have a deep depth of field, i.e. a high f-stop. So whether you know it or not, when you put your camera in landscape mode, you're controlling the f-stop!
The opposite is also true. Many camera's have a "macro mode" or closeup mode (often symbolized by a flower). This mode is telling your camera to have a smaller f-stop, and therefore a shallow depth of field.
Another way to fake a low f-stop (shallow depth of field) would be to set up your subject matter 6-8 feet away from the background. For instance... setting a coffee cup on a stool that is 8 feet from a wall will make it look like the coffee cup is in focus, but the background will have a nice blur to it. This would be especially true in your camera's macro mode.
