Effect of aperture on blur and DOF. The points in focus (2) project points onto the image plane (5), but points at different distances (1 and 3) project blurred images, or circles of confusion. Decreasing the aperture size (4) reduces the size of the blur spots for points not in the focused plane, so that the blurring is imperceptible, and all points are within the DOF.
Depth of field is the distance between the nearest and the furthest objects that are in acceptably sharp focus.[1] “Acceptably sharp focus” is defined using a property called the circle of confusion.The depth of field is determined by focal length, distance to subject, the acceptable circle of confusion size, and aperture.[2]. The approximate depth of field can be given by:
for a given circle of confusion, C, focal length, f, F-number N, and distance to subject, u.[3][4]As focal length, distance, or the size of the acceptable circle of confusion increases, the depth of field increases; however, increasing the size of the aperture reduces the depth of field. Depth of Field changes linearly with F-number and circle of confusion, but proportional to the square of the focal length and the distance to the subject. As a result, photos taken at extremely close range have a proportionally much smaller depth of field.Sensor size affects DOF only in that changing the sensor size on a camera requires changing the focal length to get the same picture. It is the change in focal length that then affects the DOF.[5][6][7]For a given subject framing and camera position, the DOF is controlled by the lens aperture diameter, which is usually specified as the f-number (the ratio of lens focal length to aperture diameter). Reducing the aperture diameter (increasing the f-number) increases the DOF because only the light traveling at shallower angles passes through the aperture. Because the angles are shallow, the light rays are within the circle of confusion for a greater distance.[8]
Points in an image produce a blur spot shaped like the aperture. Custom shaped apertures and bright points of light can be used artistically to produce images like this
Motion pictures make only limited use of this control; to produce a consistent image quality from shot to shot, cinematographers usually choose a single aperture setting for interiors and another for exteriors, and adjust exposure through the use of camera filters or light levels. Aperture settings are adjusted more frequently in still photography, where variations in depth of field are used to produce a variety of special effects.
Aperture = f/1.4. DOF=0.8 cm
Aperture = f/4.0. DOF=2.2 cm
Aperture = f/22. DOF=12.4 cm
Depth of field for different values of aperture using 50 mm objective lens and full-frame DSLR camera. Focus point is on the first blocks column.[9]
Precise focus is only possible at an exact distance from the lens;[a] at that distance, a point object will produce a point image. Otherwise, a point object will produce a blur spot shaped like the aperture, typical a circle, approximately. When this circular spot is sufficiently small, it is visually indistinguishable from a point and appears to be in focus. The diameter of the largest circle that is indistinguishable from a point is known as the acceptable circle of confusion, or informally, simply as the circle of confusion. Points that produce a blur spot smaller than this acceptable circle of confusion are considered acceptably sharp.The acceptable circle of confusion depends on how the final image will be used. It is generally accepted to be 0.25 mm for an image viewed from 25cm away.[10]For 35 mm motion pictures, the image area on the film is roughly 22 mm by 16 mm. The limit of tolerable error was traditionally set at 0.05 mm (0.002 in) diameter, while for 16 mm film, where the size is about half as large, the tolerance is stricter, 0.025 mm (0.001 in).{{sfn|[11] More modern practice for 35 mm productions set the circle of confusion limit at 0.025 mm (0.001 in).[12]
The plane of focus is normally parallel to the image plane. However, moving the lens relative to the sensor can rotate the plane of focus.When the plane of focus is rotated, the near and far limits of DOF are no longer parallel; the DOF becomes wedge-shaped, with the apex of the wedge nearest the camera. [13][14]In some cases, rotating the POF can better fit the DOF to the scene, and achieve the required sharpness at a smaller f-number. Alternatively, rotating the POF, in combination with a small f-number, can minimize the part of an image that is within the DOF.
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Bill Dobbins is a pro photographer located in Los Angeles. He is a veteran photographer and videographer who has exhibited his fine art in two museums and a number of galleries and who has published eight books, including two fine art photo books:The Women: Photographs of The Top Female Bodybuilders (Artisan)
Modern Amazons (Tashen)
WEBSITES
BILL DOBBINS PHOTOGRAPHY
www.billdobbinsphotography.com
BILL DOBBINS ART
www.billdobbinsart.com
FEMALE PHYSIQUE SITES
www.billdobbins.com
EMAIL: billdobbinsphoto@gmail.comTo have both lenses in focus, one technique would be focus stacking – combining two images, each with different points of focus and using only the areas actually in sharp focus. | Source: https://bit.ly/2XnZcrt
February 24, 2019
About the Author
Bill Dobbins
Bill Dobbins THE BODY PHOTOGAPHER became well known for his male and female physique photos - images of the aesthetic, athletic body.
Using the same distinctive personal style, characterized by strong graphics and a classic look in both color and BW, Bill Dobbins has also developed a body of work featuring fashion, beauty and glamor photos In a world in which so many images create a level of "noise" that makes it hard for advertisers to be noticed, Bill's work cuts right through the confusion and grabs the eye.
Bill has created two art photos books: The Women: Photographs of the Top Female Bodybuilders (Artisan) and Modern Amazons (Taschen) and his fine art work has appeared in two museums and several galleries.
WEBSITES
BILL DOBBINS PHOTOGRAPHY
www.billdobbinsphotography.com
BILL DOBBINS ART
www.billdobbinsart.com
THE FEMALE PHYSIQUE WEBZINE/GALLERY
www.billdobbins.com
EMAIL: billdobbinsphoto@gmail.com