If your aim is to make a photo with a blurred background or on the contrary you would prefer a very sharp photo, you should be able to change the depth of field. As you may know, the most simple way to affect the degree of blurring and the size of the sharp zone of your photo is to change an aperture. However, there are other ways as well.

To be precise, there are three main ways that can be used to change the depth of field of your image. If you learn them, you will be able to control a depth of field easily and make images without needless hustle and bustle. 

1. Adjusting an aperture

The most well-known way to control the degree of blurring of your shot is to change an aperture. The larger an aperture is the more light gets into your camera while making a shot.

If you increase the amount of light the process will be easier, you can shoot with fast shutter speed, when there is a lot of light. The more the aperture is less sharp will be an image on Z-axis in three-dimensional space. Namely, more blurred behind and at the front. That is why when you set a wide aperture a very small area will be in the zone of sharpness.

When closing an aperture (making the size of smaller), the depth of field will be increased, and so the larger area of a shot will be sharp. This happens because small aperture lets in less light, creating, as a result, a sharper image. For example, with an aperture of f/16 sharpness of the foreground and background will be almost the same. This approach is perfect for a wide-angle photo, for example for a photo of a landscape.

If you begin to change an aperture with different focal length, you can notice something strange. For example using a wide-angle lens and the values up to f/5.6 you can get photos with the background that is not very blurred. And with a telephoto lens 200mm even with f/16, you will not be able to add maximum sharpness to all objects on your shot.
This means that there is a second way to change a depth of field. 

2. Changing a focal length

When using a lens with an average focal length value (around 50 millimeters), an aperture value will have a moderate impact on the depth of field. If we take lenses with a larger range of differences in focal lengths, we can note that while changing of an aperture the sharpness of the photo remains almost the same.

If we use a long-focus telephoto lens, then even the slightest value of an aperture will not allow making foreground and background sharp at the same time. And on the contrary, a wide-angle lens, some fisheye lens will not allow you to get a shot with a small depth of field. The reason of this is a lens. A telephoto lens “squeezes” everything in the shot, that gets in the field of view. This will create a small depth of field by itself. Wide-angle lens, on the contrary, creates wider depth of field, increasing the visibility of an object within Z axis.

Actually, a lens doesn't influence on the main image; it just shows a particular angle out of the entire space available, the smaller this angle is the closer seems the objects located a different distance. So the far objects become much bigger, then the close objects and because of this compensation the image look blurred if you won’t focus on some object. These optical effects work because of the interaction between the objects that happens due to the distance on the Z axis. Any change of this distance will affect the depth of field.

3. Change of distance between an object and a camera

Place a man at the distance of half a meter from the wall. Try to create a small depth of field, so a man remains in focus and a wall is blurred. Perhaps it won’t be easy.

Surely you can use a long-focus lens and shoot from a close distance, one meter for example, with a significant zoom. So it looks like zoom and shooting from a close distance is the only effective method to create a blurred background. However, here we get a really close-up photo will one ear for example.

You can use an extremely large aperture of f/1.8, but this will decrease sharpness, and only one eye of your model will be sharp, but the nose and ears will be blurred. To avoid this we should place a man not too close to the wall. A meter and a half or two will be enough to change a situation.

The distance from your model to the wall on the Z axis will be substantially increased. This additional space will help to create a blurred background the photo will not look too blurred or too close-up.

You can change the distance of the Z-axis:

• Moving objects closer or further from the background to the foreground
• Moving the camera closer or further from the object.
• Depending on the focal length of your lens, you can increase or decrease the size of the objects in your shot to change the depth of field.

Three various ways that work together

All three methods affect the depth of field using the same principle; they affect the way the Z-axis is perceived. Instead, trying to figure out how each of these ways works independently, think how they work together.

Often when using a telephoto lens to get more narrow the depth of field of the space you try to capture, you also will have to change the distance between the objects.

Always think about how the size of an aperture will affect your shot. It is easy to forget that a large aperture creates a very small depth of field. Most likely, if you use a preview option on a small camera screen, you won't see the actual result. Only while looking through your photos on a big screen, it becomes clear that some objects are not sharp, but it's too late already.

That is why it is always recommended to make several shots with different aperture value when you have chosen a perfect shot. Thus, you will be more confident and feel certain that you haven't wasted your time even if the first shot and your choice of an aperture is not very successful.