Focal length

The focal length tells how strongly a lens, a curved mirror or another optical device brings light together or spreads it out. If rays of light go straight into a lens and the focal length is positive, the focal length is the distance to the point behind the lens where the rays will be brought to a focus. If the focal length of the lens is negative, the focal length is the distance at which the light has spread to twice its original size. Light from a large distance produces an image at F (focal point). The distance from the centre of the lens to F is the focal length.

Photography
Equipment	Camera digital instant pinhole light-field field press rangefinder SLR still TLR toy view Darkroom safelight enlarger Drone Film base format holder stock available films discontinued films Filter Lens prime zoom wide-angle fisheye telephoto Movie projector Slide projector Tripod head Zone plate Flash beauty dish cucoloris gobo hot shoe lens hood monolight reflector snoot softbox Manufacturers Monopod
Terminology	Aperture Exposure Focal length 35 mm equivalent focal length Angle of view Backscatter Black-and-white Chromatic aberration Circle of confusion Color balance Color temperature Depth of field Depth of focus Exposure compensation Exposure value Zebra patterning F-number Film format large medium Film speed Guide number Hyperfocal distance Lens flare Metering mode Perspective distortion Photograph Photographic printing Photographic processes Reciprocity Red-eye effect Science of photography Shutter speed Sync Zone System
Genres	Abstract Erotic Nature Nude Photojournalism Pornography Selfie Stock Aerial Aircraft Architectural Astrophotography Banquet Candid Conceptual Conservation Cloudscape Documentary Ethnographic Fashion Fine-art Fire Forensic Glamour High-speed Landscape Neues Sehen Pictorialism Portrait Post-mortem Ruins Social documentary Sports Still life Straight photography Street Toy camera Underwater Vernacular Wedding Wildlife
Techniques	Bokeh Cyanotype Holography Macro Multiple exposure Photogram Stereoscopy Afocal Brenizer Burst mode Contre-jour ETTR Fill flash Fireworks Harris shutter High-speed Infrared Intentional camera movement Kirlian Kite aerial Long-exposure Luminogram Mordançage Multi-exposure HDR capture Night Panning Panoramic Print toning Redscale Rephotography Rollout Scanography Schlieren photography Sabattier effect Slow motion Stopping down Strip Slit-scan Sun printing Tilt–shift Miniature faking Time-lapse Ultraviolet Vignetting Xerography Zoom burst
Composition	Diagonal method Framing Headroom Lead room Rule of thirds Simplicity Golden triangle (composition)
History	Timeline of photography technology Analog photography Autochrome Lumière Box camera Calotype Camera obscura Daguerreotype Dufaycolor Heliography Painted photography backdrops Photography and the law Glass plate Visual arts
Digital photography	Digital camera D-SLR comparison MILC camera back Image sensor CMOS APS CCD Three-CCD camera Foveon X3 sensor Image sharing Pixel Digiscoping Comparison of digital and film photography Film scanner
Color photography	Color Reversal film Color management primary color CMYK color model RGB color model color space Print film Chromogenic print
Photographic processing	C-41 process Bleach bypass Cross processing Developer Digital image processing Dye coupler E-6 process Fixer Gelatin silver process Gum printing Instant film K-14 process Print permanence Push processing Stop bath
Lists	Most expensive photographs Museums devoted to one photographer Photographs considered the most important Photographers
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Related	Conservation and restoration of photographs film photographic plates Lomography Polaroid art Outline

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