4.3 Focal length and depth of field

Focal length and depth of field are key concepts in photojournalism. They shape how we capture and present stories visually, influencing everything from the angle of view to subject isolation.

Understanding these elements allows photographers to make creative choices. Wide-angle lenses exaggerate depth, while telephotos compress perspective. Shallow depth of field isolates subjects, while deep focus keeps everything sharp.

Understanding Focal Length

Focal length and image effects

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• Focal length measures distance between lens optical center and image sensor in millimeters affects angle of view and image compression
• Shorter focal lengths produce wider angle of view capturing more of the scene (28mm lens)
• Longer focal lengths create narrower angle of view magnifying distant subjects (200mm lens)
• Shorter focal lengths enhance depth perception exaggerating perspective (16mm wide-angle)
• Longer focal lengths compress perspective making objects appear closer together (300mm telephoto)
• Focal length directly impacts subject magnification longer lengths increase magnification shorter lengths decrease it

Types of lenses in photojournalism

• Wide-angle lenses (14-35mm) exaggerate depth and perspective ideal for environmental portraits and landscapes capture more in tight spaces (24mm for street scenes)
• Standard lenses (35-70mm) mimic human eye perspective versatile for everyday photojournalism natural-looking portraits and street photography (50mm for general use)
• Telephoto lenses (70mm+) compress perspective and isolate subjects used in sports wildlife photography and candid shots from a distance (200mm for wildlife)

Depth of Field and Focus Techniques

Factors influencing depth of field

• Depth of field defines range of acceptable sharpness in an image
• Aperture wider (f/1.8) decreases depth of field narrower (f/16) increases it
• Focal length longer decreases depth of field shorter increases it
• Subject distance closer subjects decrease depth of field further subjects increase it
• Sensor size larger sensors (full-frame) produce shallower depth of field smaller sensors (crop) produce greater depth of field

Selective focus for emphasis

• Shallow depth of field isolates subject from background creates pleasing bokeh effect (f/2.8 for portraits)
• Zone focusing pre-focus on specific distance useful for street and action photography (f/8 at 10 feet)
• Hyperfocal distance maximizes depth of field for landscapes calculated using focal length and aperture
• Focus stacking combines multiple images with different focus points achieves greater depth of field in macro photography
• Tilt-shift techniques manipulate plane of focus create miniature effect or correct perspective (architectural photography)