Week 5

Review

Lenses

Why Use Different Lenses?

• Focal Length

• Wide Angle

• “Normal”

• Tele

• “Speed”

• Fast - Heavy

• Slow - Light

Why?

• Purpose

• Macro

• Zoom

• Specialty Lenses

What is Focal Length?

http://en.wikipedia.org/wiki/File:Focal-length.svg

“Normal”

• Renders a scene very similar as experienced by the unaided human eye

• Front to back spacing between objects

• Relative size of objects

What is “Normal”?

• Subjective

• With 35mm film, a 50mm lens was considered “normal”

• With DSLR (or any non-35mm format) we need to correct for the sensor size

Sensor Sizes

Sensor Size CorrectionCamera Crop Factor

Full Frame 1.0

Canon DSLR 1.6

Nikon DSLR 1.5

iPhone 5 8.05

Canon: 50mm lens appears like 50mm*1.6 = 80mm

Wide Angle Lens

• Short Focal Length

• Less Mangification

• Greater Field of View

• Depth perception distorted by expanding the apparent distance between objects

Telephoto

• Longer Focal Length

• More Magnification

• Smaller Field of View

• Depth perception distorted by compressing the apparent distance between objects

MacroObject projected on the sensor is of equal size or larger than the object.

Equal size is called a reproduction ratio of 1:1

Numbers on My Lens

• There are two important numbers or number pairs on a lens

• Focal length in mm (e.g. 50mm)

• Max. aperture (e.g. f/3.5)

• Can show up as pairs: 28-135mm/3.5-5.6

Lens Applications

• Landscape

• Portraits

• Wildlife

• Close-ups

• Macro

28mm 70mm

50mm 210mm

Expanded

Normal

Compressed

Depth Of Field

Circle of Confusion

• Any lens is only in focus at exactly one distance from the lens

• An out of focus point produces a blurred circle.

• If the “Circle of Confusion” is small enough, our eyes still consider things in front and behind that theoretical point as in focus

• This is called the “Acceptable Circle of Confusion”

What is DOF?

http://en.wikipedia.org/wiki/File:Depth_of_field_diagram.png

http://en.wikipedia.org/wiki/File:DOF-ShallowDepthofField.jpg

What Affects the DOF?

• Focal Length

• Aperture

• Format

Demo

Depth of Field Preview

Some Camera Function

Exposure or Program Shift

• Shift from one exposure to an equivalent one

• If 1/125s and f/5.6 is the “correct” exposure, then 1/250s and f/4 is correct as well, as is 1/60s and f/8

• Most DSLR cameras can do this automatically

• Control DOF or motion blur

Canon

Nikon

Auto Exposure Lock

Nikon

Auto Exposure Lock

Canon

Focus Modes

• Single Shot

• Continuous

• Predictive

• AF Lock

• Manual

Drive Mode

• Single Shot

• Continuous

• High

• Self Timer (2s, 10s)

JPEG vs RAW

Sensor RAW Processor RAW Memory

Sensor RAW Processor: White Balance Color Space Bit Depth

Compression

JPEG Memory

JPEG vs. RAW

• JPEG images can be used right away

• RAW images require post processing

• JPEG images can not be “squeezed” for more information

• RAW images can be processed differently than the camera would have, and can reveal much more information

• JPEG images are much smaller, can store more images on memory card

• The best of both worlds: Use JPEG+RAW

Field Trip 2

Assignments

• Use the program or exposure shift feature to take pictures of the same scene with different DOF or blur effects.

• Use different aperture settings for several pictures of one scene to explore the depth of field behavior. Remember to adjust the shutter speed accordingly.