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To render closer objects in sharp focus, the lens must be adjusted to increase the distance between the rear principal plane and the film, to put the film at the image plane. The focal length f, the distance from the front principal plane to the object to photograph s 1, and the distance from the rear principal plane to the image plane s 2 are ...
The depth of field, and thus hyperfocal distance, changes with the focal length as well as the f-stop. This lens is set to the hyperfocal distance for f /32 at a focal length of 100 mm. In optics and photography, hyperfocal distance is a distance from a lens beyond which all objects can be brought into an "acceptable" focus.
Image distance in a spherical mirror + = () Subscripts 1 and 2 refer to initial and final optical media respectively. These ratios are sometimes also used, following simply from other definitions of refractive index, wave phase velocity, and the luminal speed equation:
Diagram illustrating the flange focal length of an SLR–type and a mirrorless–type camera. For an interchangeable lens camera, the flange focal distance (FFD) (also known as the flange-to-film distance, flange focal depth, flange back distance (FBD), flange focal length (FFL), back focus [1] or register, depending on the usage and source) of a lens mount system is the distance from the ...
The distance between an object and a lens. Real object Virtual object s i: The distance between an image and a lens. Real image Virtual image f: The focal length of a lens. Converging lens Diverging lens y o: The height of an object from the optical axis. Erect object Inverted object y i: The height of an image from the optical axis Erect image ...
where t is the total depth of focus, N is the lens f-number, c is the circle of confusion, v is the image distance, and f is the lens focal length. In most cases, the image distance (not to be confused with subject distance) is not easily determined; the depth of focus can also be given in terms of magnification m: = (+).
The effective focal length is nearly equal to the stated focal length of the lens (F), except in macro photography where the lens-to-object distance is comparable to the focal length. In this case, the absolute transverse magnification factor ( m ) ( m = S 2 / S 1 {\displaystyle m=S_{2}/S_{1}} ) must be taken into account:
A simple method to find the rear nodal point for a lens with air on one side and fluid on the other is to take the rear focal length f ′ and divide it by the image medium index, which gives the effective focal length (EFL) of the lens. The EFL is the distance from the rear nodal point to the rear focal point.