Standard Lens For a 35mm camera the standard lens is 50mm. It is called the standard because the perspective it produces in the image is closest to that seen by the human eye. 50 mm focal length
DEPTH OF FIELD IS: the area of acceptable sharpness in a picture Changing the aperture size affects the sharpness of the image as well as the amount of light that enters the camera. As the aperture gets smaller, more of the image becomes sharp. Focal distance also affects depth of field. The greater the focus distance from the camera to the subject, the greater the depth of field.
A wider aperture (smaller f-stop number) will result in a shallower depth of field. You can use this to keep either the foreground or background out of focus while maintaining the subject in focus. When changing the aperture setting, you will need to also adjust the shutter to maintain the correct exposure. Aperture = F5.6 Shutter = 1/1000 Little/Shallow depth of field Aperture = F22 Shutter = 1/60 Greater/More depth of field