In Photography, the depth of field refers to the area of sharp focus in a photograph. You can create photographs which are fully in focus throughout (large depth of field) or which have a small area sharply focused but the rest is blurred (small depth of field) or photographs which may have a mix of half and half (medium depth of field).
Adjusting the aperture on your camera is one factor which allows you to change the depth of field. However, if your camera is fully automatic it can be difficult to achieve depth of field effects or if you need to change the depth of field on an existing photograph, that’s where Photoshop comes in.
In this quick, simple tutorial, we’ll manipulate a photograph to give a sharp foreground (the face) and a blurred background (the rest of the body).
2. Duplicate the layer by pressing Ctrl + J (windows) or Cmd + J (mac) in the Layers palette.
3. Choose Filter > Blur > Gaussian Blur and when the dialog box opens increase the Radius to about 10 pixels so that the entire image is blurred.
4. Now we can use a Layer Mask to reveal part of the untouched layer at the bottom of the Layer stack. On the Layer palette, click on the Add Layer Mask icon.
When the Layer Mask thumbnail is added, click on it to ensure the Layer Mask is selected rather than the whole layer.
5. In the toolbar, select the Brush Tool, set the Foreground color to black and in the Options bar set it a round tip of 300 pixels and 0% hardness.
6. Start painting on the baby’s face and you will see the Sharpness from the original image.
7. Keep painting until the baby’s head is fully sharp but the rest of it’s body is left blurred. And your final image should look something like this.