Why does aperture affect depth of field

At that point the imaging system performs in accordance with losses such as atmospherics and the MTF modulation transfer function of the lens. As an object moves off that plane, it immediately becomes "out of focus" and there is a point spread function which describes a growing disk which is in some circles no pun intended called the "circle of confusion. Smaller apertures employing central portions of the lens, have the light taking a shorter and more consistent path through the lens. This helps reduce the point spread function which describes the circle of confusion and not always a circle.

The point spread function of an optics system is also called the impulse response. The resultant image is one which is the convolution of the target image and the point spread function. At least for non-coherent imaging. So the perception of the depth of field is linear with the f-stop and focal length. Unfortunately, depth of field has it limits, and a very very small aperture will not provide nearly infinite depth of field, because diffraction plays a greater role, in blurring the image, as the aperture gets smaller.

So what really happens with depth of field is that objects are not really in focus off the focused plane, but rather the blur is considered negligible. Think of it this way: a thumbnail photo might look clear, but if expanded to be an 8x10" photo, it may be unacceptably fuzzy. In practical application, a so-called hyper-focal setting on a lens, may give an acceptable image of a scene when viewed on a small format display or print, but when expended or enlarged, will yield a more fuzzy appearance as it is in reality not completely in focus through the "depth of field.

As a photographer and physicist myself, I am trying to explain this phenomenon to my musician friend who has just bought an expensive camera.

The best I can come up with is to take, at the extreme, a pinhole camera with infinite depth of field. As we stick a lens in front and widen the aperture it becomes closer to the familiar situation with object and image distance determined by focal length.

Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. In every picture there is a certain area of your image in front of, and behind the subject that will appear in focus.

This zone will vary from photo to photo. Some images may have very small zones of focus which is called shallow depth of field. Others may have a very large zone of focus which is called deep depth of field.

Three main factors that will affect how you control the depth of field of your images are: aperture f-stop , distance from the subject to the camera, and focal length of the lens on your camera. As soon as an object person, thing falls out of this range, it begins to lose focus at an accelerating degree the farther out of the zone it falls; e.

Shallow is when the included focus range is very narrow, a few inches to several feet. Deep is when the included range is a couple of yards to infinity. In both cases DOF is measured in front of the focus point and behind the focus point. DOF is determined by three factors — aperture size, distance from the lens, and the focal length of the lens.

You may have seen this principle demonstrated when you look at photos taken outside during the brightest time of the day. Aperture refers to the access given to light from the lens to the camera sensors.

Inversely, the farther away the subject is from the camera, the wider the depth of field will be. The following graphic illustrates how changing these factors: aperture, focal length and the distance from the subject affect the depth of field. Infographic illustrates how changing the aperture, the focal length and the distance from the subject affect the depth of field. Expand All Shallow Depth of Field. In this image you can see how a shallow depth of field keeps the focus on the action.

Photo by Samuel King In this image you can see how a shallow depth of field keeps the focus on the action. Medium Depth of Field.

In this image a medium depth of field allows the viewer to focus on multiple subjects without creating confusion for your eyes Photo by Sebastian J. Sciotti Jr. In this image a medium depth of field allows the viewer to focus on multiple subjects without creating confusion for your eyes Download Image Share Image: Twitter Facebook Email Photo by: Sebastian J.

Deep Depth of Field. In this image a deep depth of field allows the viewer to take in many subjects, including an artillery shell mid-flight.

Photo by Staff Sgt. Steven Schneider In this image a deep depth of field allows the viewer to take in many subjects, including an artillery shell mid-flight.