Lesson 1: The Art and Physics of Photography

1. Lesson 1:The Art and Physics of Photography Digital Photography MITSAA IAP 2003 Rob Zehner

2. General Info • Instructor: Rob Zehner (zehner@pobox.com) • Meeting time: 7:00 - 8:30 p.m. every Wednesday • We will meet in front of the SAA office • Please bring any borrowed equipment with you to class every week

3. Outline • How the camera works • lens • shutter • aperture • film • How the digital camera works • Some rules of thumb for good photos

4. The Camera virtual image image lens aperture

5. The Lens • Purpose: to collect light from the sample and focus it on the film plane • Focal length: distance from the lens to the film plane (for a single-element lens) when focused at infinity • Longer focal length = more magnification

6. The Shutter • Prevents light from reaching the film • Opens to allow light through • In most cameras, the shutter is actually two pieces of cloth or metal that move across the film plane, one after the other • Shutter speeds are usually reported as reciprocal seconds, e.g. 1000 = 1/1000th sec.

7. The Shutter, continued • Shutter speed determines relative effects of motion • Slow shutter speeds = blurry images • Fast shutter speeds = stopped motion • Rule of thumb: 1/60th or faster will eliminate the effects of shaky hands • Also determines film exposure • 2X shutter speed = 1/2 the light to the film • 1/2 the shutter speed = 2x the light to the film

8. The Aperture • Placed at the focal point of the lens • Typically a circular opening • Diameter of circle determines amount of light that gets to the film • Reported as f-number - ratio of focal length to aperture • Larger f-number = smaller opening

9. The Aperture, continued • Size affects “depth of field” - distance in front of and behind the focal plane that is in focus • Small apertures (large f number) = greater depth of field • Size also affects film exposure • Increase of 1 stop (x 1.414) = 1/2 as much light • Decrease of 1 stop (1.414) = 2x as much light

10. The Film • The film’s job is to detect light • Photons hit the film and promote a reaction • Film speed is typically reported in ASA • Higher ASA = “faster” film - needs less light • Doubling ASA = 1 stop less light needed • Rule of thumb - “sunny f16 rule” • Under bright sun, use f16 and 1/ASA shutter • Generally, film with a higher ASA is grainier

11. Digital differences • Film is replaced by an image sensor • Photons hit the sensor and create charge, which is converted to voltage, which is converted to bits • All image sensors are actually analog • Shutter may be electronic, not mechanical • Image sensors are subject to thermal noise • Long exposures may not be possible

12. Digital differences, continued • For now, image sensors are smaller than film • Image size is a function of focal length vs. sensor size • Small sensor = short focal length • Short focal length means it’s hard to get small apertures • Short focal length means that depth of field is relatively larger at all apertures

13. The Rule of Thirds

14. Other tips for good photos • Use natural light • Avoid on-camera flash as much as possible • Find new perspectives • Move around • Take horizontal and vertical shots • Find converging lines • Play with negative space • Take candid portraits • When in doubt, bracket exposures