Understanding How to use F-stop (Aperture) in Photography
What is f-stop and aperture? Aperture and f-stop are often used interchangeably but they aren't technically the same. If you want to learn more about the technicalities of the two read this article by DP Review. For the sake of this article we are going to focus on the question of "what is f-stop?" This question can be the single reason why people shy away from learning to shoot manual with their mirrorless or dslr camera. So let's talk about it.
I think it is best to start off talking about how the f-stop affects depth in your image. When I am photographing a model I am shooting with a shallow depth of field so my f-stop is generally set between f1.4 and f4. This will make the model stand out from the rest of the scene and make the model the main focus of the image. This same technique can be used for emphasizing specific objects or parts of an image as well. Lets take a look at the images below and see what is going on here.
If you look closely at these images you can see that the image shot with an f-stop of f1.4 has a blurred out background. At f1.4 the depth of field is very shallow so it emphasizes the focus on the subject which in this case is the lifeguard tower. When you look at the second image at f13 you can see there isn't as much depth to the image which means there isn't much background blurring occurring behind the subject. You can see detail in the water and boats behind the tower at f13. This is emphasized in the last two photos where I cropped in to show the details between the tower and the boats in the background. In the third to last photo you can see that the number "16" on the boat is in focus and that the boats in the background are not in focus. Shooting at a 1.4 will create that look. In the last photo you can see that the number "16" on the tower is in focus and the boats in the background are also in focus. At f13 you can make out the letters and details on the boats and at f1.4 the boats are just a blurry blob in the shape of a boat. Lets take a look at some more images.
In the image above we have Ashlyn (her IG is linked) posing along the shore and I shot this at f1.4. She is completely in focus while everything else is significantly blurred and out of focus in the background. This is purely intentional. I wanted to completely separate the model from the background and make her pop out from her coastal surroundings. Now let's look at a photograph that I took where the emphasis isn't all on the subject but instead incorporates the subject into the scene.
I want to state that the first picture at the top is the full image. The second is cropped in to focus on the subject and skyline. The third is cropped in to focus on the bridge and skyline behind it. This isn't the sharpest picture ever but it will work fine for this example. At f13 the subject (Photographer Zach Matthai) in the foreground is in focus and the parts of the image beyond the subject are also in focus (the skyline and the bridge). If I were to shoot this same photo in f1.4 like the photo of Ashlyn on the beach then the subject would be in focus while everything else would be out of focus.
So f1.4 to f4 creates a very shallow depth of field. As you go from f4.5 to f10 that depth of field quickly diminishes and more parts of the image come into focus. When you go from f13 to f22 the depth of field completely changes and everything comes into focus.
I typically shoot portraits or any photo with a person in it at a shallow depth of field. If I want the background completely blurred out I will shoot at f1.4 to f2.8. If I want to show a little more of the background in the shot I will shoot at f3.2 to f4. Occasionally I have shots like the one above with the photographer at the Golden Gate Bridge where I shot at f13 because I want everything in focus to really show off the whole scene. When I am shooting landscapes I am typically shooting from f11 to f16 because I want as much in focus as possible. I will shoot at f7 to f10 for some landscapes if needed but that usually just depends on the lighting and my shutter speed balance. On that note, I think it is time to start talking about how f-stop affects the lighting.
Before we get into it here is a great cheat sheet I found from www.clickandlearnphotography.com that easily sums up how f-stop affects both depth of field and light.
Let's talk about how f-stop affects the light and the brightness of an image. You can see how the chart explains what we learned above with the depth of field and now you can see how it affects the light as well. When you are shooting at f1.4 the eye of the lens is wide open so it is letting a lot of light in. As the f-stop goes to an f4 and all the way to an f22 the eye of the lens continues to close more and more therefore letting in less light. The amount of light coming in and the depth of field go hand and hand when it comes to f-stop. This is why shooting in manual mode is a game of balancing the f-stop, shutter speed and iso to get the right depth of field and the correct lighting, But we will get more into those technicalities of photography later.
Now is a good time to grab your camera and start playing with the f-stop. I suggest putting the camera into shutter priority mode. It will be best if you are in an area where there is a spot with really bright light and a spot where its a little darker. Now point at the bright scene and take a picture. If it is too bright raise your shutter speed up to darken the image to where it is properly exposed. Once you have your shutter speed set the camera will only change the f-stop to balance the lighting. If you are pointing the camera in a direction where there is a lot of light coming into the lens the camera will automatically adjust the f-stop to compensate it. So if the f-stop is at f4 and the camera senses that there is too much light coming in it might adjust the f-stop to f7. If the camera is at f7 in bright light once you moved it back to a darker area with less light the camera might adjust the f-stop back to f4. If you have a mirrorless camera you can just look at the back of your lcd screen or through the eye hole to watch the camera make these adjustments. If you have a dslr you will have to take a picture each time and review the photos to see the differences. Test this method in different areas and notice the amount of light there is and how your f-stop is being adjusted automatically by the camera.
This techinique should give you the ability to understand how the f-stop adjusts to compensate for different llighting situations. Don't forget to pay attention to the depth of field and test that as well. Shoot wide open landscapes and as well as images with a subject in the foreground so you can really see how the depth of field is adjusting. After doing that for a while try shooting in aperture priority. This will give you the ability to to pick a specific f-stop to shoot in and the camera will then decide the shutter speed to determine how much light is needed to expose the camera. These tests are best to do in an area with plenty of light so that the shutter speed doesnt slow down too much which could make images blurry if you are shooting handheld. This will then be a good way to segway into learning all about shutter speed in the next blog post. Just give yourself the time to play with these methods and you should get a good feel for how the f-stop affects your photographs.
I will be explaing all of this in an upcoming YouTube video so join my channel and stay tuned. Also, if you have any questions feel free to send me a message and I will help you out.
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