What is Diffraction?Light travels in waves, diffraction occurs when lightwaves encounter an obstacle resulting in the bending of the lightwaves as they spread out past an opening. In the case of a photographic lens this bending of lightwaves occurs when light passes through the lens aperture. Diffraction increases as lightwaves passing through a smaller aperture When the aperture is made smaller by 'stopping down' the lens past a specific aperture diffraction becomes noticable, resulting in a softening of the image and a reduction in resolution. The aperture at which diffraction occurs will vary depending on the combination of lens and camera used. The effects of diffraction are partly influenced by the size of the pixels on the camera’s image sensor.Stopping down the aperture has another effect as it increases the depth of field, bringing both the foreground and the background into focus. So resolution will increase to a certain aperture as depth of field increases and lens aberrations are reduced. Diffraction increases as the lens is stopped down further past the aperture at which the optimal resolution occurs and will increasingly effect resolution as the aperture is stopped down further.The example below demonstrates how resolution changes with images taken at varying apertures. The focus point is on the right eye as we look at the image. Enlaging this section to 100% shows how resolution decreases past a specific aperture. In this test an aperture setting of f/8 produces the highest resolution with this combination of camera and lens. Full image taken at f/2.8 with a shallow depth of field Crop of above image enlarged to 100%.At f/2.8 the resolution of the eye and eye lashes is average At f/8 the resolution on the eye and eyelashes is at its highest At f/22 the resolution of the eye is high, but there is a softening of the image caused by diffraction which can be seen in the eyelashes When achieving the highest resolution is important, the choice of aperture is a key consideration. The aperture set on the camera controls not only the amount of light entering the lens and depth of field, but also the degree of aberration and diffraction, it is important that the aperture setting is selected with careful consideration of all of these factors. Choosing the optimal aperture with a specific lens will help retain the quality of the high resolution sensors being used in many of the latest digital SLR cameras. Print Share By Email Share By Social Ask A Question FaceBook Twitter