Difference between revisions of "Diaphragm"
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{{glossary}} | {{glossary}} | ||
| − | A '''diaphragm''' (or '''iris''' or ''iris diaphragm'') is a mechanism in a camera that makes a variable [[aperture]] to control the | + | {{Flickr_image |
| + | |image_source= http://www.flickr.com/photos/dustymedusa/3742807840/in/pool-camerawiki | ||
| + | |image= http://farm3.static.flickr.com/2566/3742807840_39acc22b65.jpg | ||
| + | |image_align= right | ||
| + | |image_text= an 8-bladed iris diaphragm | ||
| + | |image_by= Dusty Medusa | ||
| + | |image_rights= with permission | ||
| + | }} | ||
| + | A '''diaphragm''' (or '''iris''' or ''iris diaphragm'') is a mechanism in a camera that makes a variable [[aperture]] to control the intensity of light that passes through the lens. Along with [[shutter speed]], this is what controls the exposure received by the film or image sensor. | ||
| − | A diaphragm may take many forms, from very simple devices for "point-and-shoot" film cameras consisting of just two notched pieces of metal, to more complex ones used in higher-quality cameras which have many blades arranged in a circle. This arrangement, also called an "iris" after the corresponding structure in the eye, creates a nearly-circular aperture whose size can be varied as needed. There may be as few as 5 blades to as many as 19. In cameras with a small number of diaphragm blades, the shape of the aperture itself (a | + | A diaphragm may take many forms, from very simple devices for "point-and-shoot" film cameras consisting of just two notched pieces of metal, to more complex ones used in higher-quality cameras which have many blades arranged in a circle. This arrangement, also called an "iris" after the corresponding structure in the eye, creates a nearly-circular aperture whose size can be varied as needed. There may be as few as 5 blades to as many as 19. In cameras with a small number of diaphragm blades, the shape of the aperture itself (e.g. a hexagon) can often be seen in defocused points of light. |
| − | + | To transmit a particular light intensity, the physical diameter of the aperture must scale up with increasing lens [[Lens#Focal length|focal length]]. Thus, apertures are expressed by the [[f-stop]] scale or "F-ratio," which is the focal length divided by the [[entrance pupil]] diameter provided by the diaphragm opening. | |
[[Category: Camera parts]] | [[Category: Camera parts]] | ||
Revision as of 14:26, 23 February 2011
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| an 8-bladed iris diaphragm image by Dusty Medusa (Image rights) |
A diaphragm (or iris or iris diaphragm) is a mechanism in a camera that makes a variable aperture to control the intensity of light that passes through the lens. Along with shutter speed, this is what controls the exposure received by the film or image sensor.
A diaphragm may take many forms, from very simple devices for "point-and-shoot" film cameras consisting of just two notched pieces of metal, to more complex ones used in higher-quality cameras which have many blades arranged in a circle. This arrangement, also called an "iris" after the corresponding structure in the eye, creates a nearly-circular aperture whose size can be varied as needed. There may be as few as 5 blades to as many as 19. In cameras with a small number of diaphragm blades, the shape of the aperture itself (e.g. a hexagon) can often be seen in defocused points of light.
To transmit a particular light intensity, the physical diameter of the aperture must scale up with increasing lens focal length. Thus, apertures are expressed by the f-stop scale or "F-ratio," which is the focal length divided by the entrance pupil diameter provided by the diaphragm opening.
