Sue Barthelow'sArticles For Photographers |
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Landscapes - Managing Depth of Focusby Sue BarthelowHave you been unsuccessful when you included a foreground object in a landscape photo? You expected everything from your close object to the background to be in focus? You discovered that either your object or your background didn't come out as you wanted. Then this article is for you. This article won't help you understand everything about landscapes. However, it will help you to be more successful with those landscape images that need a deep focus region. F-Stop SettingYou probably already know that your f-stop setting relates to the depth of focus you get in your image. Set the f-stop to a small value (wide lens diameter) and you get a shallow depth of focus. The spot you focus on is sharp while objects in front of and behind that spot are out of focus. Set the f-stop to a large value (small lens diameter) and most if not everything in your image is in focus. In other words, when you focus on a point, your image has sharp regions both in front of and behind your focus point. The depth of your sharp focus region depends on your lens' aperture and thus on your f-stop. How It WorksDepth of focus, f-stop and your lens' focal length are all mathematically related. If you know your lens' focal length and the f-stop you want to use, you can calculate a value called hyperfocal distance. Something located at the hyperfocal distance is sitting at your hyperfocal point. That something is between your foreground (a nearby object you want to be sharp) and your background (the distant scene). The hyperfocal distance is the distance to something you need to focus on in order to end up with both a nearby object and a distant scene in focus. An important thing to pay attention to concerning the hyperfocal distance is that the nearby object you want to be in focus needs to be within ½ the hyperfocal distance from the hyperfocal point. If your object is closer to you than it is from the point you focus on, it will not be sharp. Another thing you need to know is that there's actually more than depth of focus, f-stop and lens focal length involved in the mathematical equation used to calculate hyperfocal distances. The equation includes a constant referred to as the circle of confusion. Now that's an appropriate name isn't it. Anyway, the constant is based on how your camera is made. So, your camera make and model go into the equation too. What It All MeansHere's an example that works for many Nikon cameras. Let's imagine that you're using a Nikon camera to take a landscape photo and are using a 24mm focal length lens (either a fixed lens or set to 24mm on a zoom lens). The table shown below has been specially prepared for the example. This table is specific to many Nikon cameras and to a 24mm focal length lens. It doesn't work for all cameras and it only works for the 24mm lens.
In this example, if you want your image to include a sharply focused object that is located about 3 feet in front of the camera along with the background landscape, you can set your f-stop to f/16 and then focus on something about 6 feet away. Anything lower than f/16 (f/8 to f/14) won't work for you unless you can move farther away from the nearby object. Want to use f/11? That works as long as you move back so your object is 4 1/3 feet away and then focus on something about 8 2/3 feet away. If you want to use f/22, you can get almost as close as about 2 feet away from your object and focus on something about 4 1/3 feet away. How do you know? The chart tells you. You can do one of two things. You can look at your desired f-stop and then look down the column at the distances. Or, you can look at the row labeled "Sharp at" and find the closest fit to the object's distance and then read up the column for the focus distance and f-stop. Take some landscape pictures using your camera and lens along with a set of tables that are made for your camera. Find a nearby object that sits in front of a long distance scene. Use your camera's tables to set your shots up. After a while, you'll get the hang of it and start remembering how to set the shot up without referring to the tables. Finding Your TablesWant to get a copy of a set of hyperfocal distance tables that work with your camera? I calculated several using available web tools. Click on the one that works for your camera or circle of confusion constant. Look for your camera listed below and then click on "Get Tables".
Get Tables
Circle of Confusion Constant: 0.019
Get Tables
Circle of Confusion Constant: 0.020
Get Tables
Circle of Confusion Constant: 0.023
Get Tables
Circle of Confusion Constant: 0.030
Get Tables
Circle of Confusion Constant: 0.005 |
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