Transcript Lesson 3: The Art and Physics of Photography

Lesson 1:
The Art and Physics of
Photography
Digital Photography
MITSAA
IAP 2003
Rob Zehner
General Info
• Instructor: Rob Zehner ([email protected])
• 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
Outline
• How the camera works
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lens
shutter
aperture
film
• How the digital camera works
• Some rules of thumb for good photos
The Camera
virtual image
image
lens
aperture
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
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.
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
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
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
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
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
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
The Rule of Thirds
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
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Find converging lines
Play with negative space
Take candid portraits
When in doubt, bracket exposures