depth of field - Mathematical relation between aperture and DOF - Photography Stack Exchange
For our purposes here, we tackle aperture and depth of field to help you build a the relationship between the f-stop and the size of the corresponding aperture. Getting the right depth-of-field for your photos requires an understanding of both aperture and focal length. Here's a quick primer. Large aperture = Small f-number = Shallow (small) depth of field The result of this should also help give you a fast enough shutter speed to freeze the action.
The bigger the actual size of the aperture can get the larger the opening the "faster" the lens is considered. When you hear about a "fast" lens, someone is talking about a lens with a big maximum aperture opening.
The picture below shows what that will do to the depth-of-field: You still focused your camera on the girl in front but now the girl to the right is sharp too even though you did not change your focus point.
The depth-of-field, or zone of sharp focus, now extends past the girl in front and covers the girl in back. But, also notice that the boy to the left is still not in focus.
The background is not in focus either. Now everything in the picture is sharp.
Remember, you focused on the front girl's face in all these pictures. So, Depth-of-Field is simply the zone of sharp focus. But in the landscape image immediately above, a small aperture i. Note in the landscape image how everything in the scene is nice and sharp, from the flowers in the foreground to the distant mountain peaks. This is beneficial when photographing landscapes such that the viewer gets the full scope of details of the landscape they are seeing.
In short, the larger the f-number, the larger the depth of field. The smaller the f-number, the shallower the depth of field. If you still find yourself struggling to remember how aperture and depth of field are related, have a look at the video below by TechQuickie, in which they explain all the concepts above in under three minutes: Problems With Aperture There are a few caveats about aperture that you need to know that will help you get the best shots possible.
Though it might be tempting to use the largest aperture your lens can handle to minimize depth of field, or conversely, using the smallest aperture possible to get the largest depth of field, that's often not advisable. The reason for this is simple: Specifically, your images can be on the soft side when shooting at the maximum or minimum aperture, which simply means that they aren't as sharp as they could be.
This has to do with the lens's sweet spotwhich is the aperture at which you get the sharpest results. But what is common to all lenses is that the maximum and minimum apertures will not be the sharpest.
So, no matter what sort of photo you wish to create - a portrait, a landscape, or something in between - remember that avoiding the extremes of aperture, even by just one stop, can make a huge difference in the sharpness of your photo.
The landscape above, for example, shows excellent sharpness throughout because the photographer avoided using an extreme aperture in favor of one closer to the lens's sweet spot. Also remember that as you manipulate the aperture, that not only is depth of field and sharpness impacted, but so too is the amount of light entering the lens.
When you shoot in full auto mode, your camera makes all the necessary adjustments such that the aperture, shutter speed, and ISO work together to get a well-exposed image.
But, full auto isn't the most advantageous mode to take pictures because you have no say regarding the camera's settings. Fortunately, you can take more control by shooting in aperture priority mode. A Quick Explanation Basically, aperture priority mode is a semi-automatic shooting mode that lets you decide the aperture while the camera selects a shutter speed that results in a well-exposed image.
It's a great way to learn to take more control over your camera settings but without having the stress of shooting in full manual mode. Doing so locks that aperture value in and tells the camera to select a shutter speed to match, such that the resulting image, like the one above, has the shallow depth of field you want and is well-exposed too.
If it sounds scary, it's not! Here's a quick summary of aperture priority mode and depth of field by Phillip McCordall: How does distance control depth of field? The closer your subject is to the camera, the shallower your depth of field becomes. Therefore, moving further away from your subject will deepen your depth of field. How does the focal length of a lens control depth of field?
Focal Length refers to the capability of a lens to magnify the image of a distant subject.
Understanding DOF and Aperture & Shutter Speed Relationships
This can get complicated, but the simple answer is that the longer you set your focal length the shallower the depth of field. If you zoom into mm from the same spot, the depth of field changes to 9.
Even with a point and shoot camera, there are ways to control your depth of field. In the Scene Modes menu, look for a symbol of a human head, which is the setting for portraits.
This will give you a narrow depth of field. In the same menu there is also a mountain symbol, which is a setting for landscapes, which will give you a deeper depth of field.
If you are a beginner with a DSLR there are some simple ways you can control depth of field and still use and automatic shooting mode. By choosing Aperture Priority mode you can set your aperture to get the depth of field that you want, and the camera will automatically set the shutter speed.
Understanding DOF and Aperture & Shutter Speed Relationships
Can I set the depth of field exactly for each situation? Yes, but because changing your aperture affects your shutter speed, the result may not meet the needs of your image. Understanding how all these settings work together can increase your control over depth of field. Is depth of field equally distributed in front and back of my focus point?