More fun with lenses!

Max Aperture
- Ratio = max aperture diameter : lense focus length
- for every 1mm of aperture diameter there is 1.4mm focal length

Relative lens Aperture
- Each f-number is related to the focal length

Lens Aberrations
-an aberration is an optical error
-no lense is perfect
many aberrations can be corrected by inducing alternative errorsin the lens
-some errors are welcomed (soft focus lens)
-different wavelengths do not focus at the same point

Chromatic Aberations
-light passing through glass is dispersed into colours
-Axial (logitudinal) and transverse (lateral)
-common in long and wide lenses


Axial chromatic aberations
-can be reduced by careful use of other aberations
-chromatic lense types
*Achromatic = blue and green
*Apochromatic = blue green red
*Superachromatic = IR B G R

Coma
-an off axis aberation creating cone shaped points
-stopping down can slightly reduce effect
can be reduced through deliberate use of other aberations

Asigmatism
-off axis aberation causing vertical and horizontal lines to be focused in two different planes
-reduced slightly by stopping down

Distortion
-sharpness is not affected


Geometric distortion
-when the objects at the edge of a field of view are stretched to fit a film plane

Curvature of field
-lens cannot focus on image of a flat object on flatplane
-focused image is formed in a bowl shape
-stopping down slightly reduces this

Lense Types

Wide angle
A lens whose focal length is substantially shorter than an average lens.

Zoom
Lens with the ability to adjust its focal length.

Long focus
Able to take photos of very distant subjects.

Telephoto
A long focal length lens in which the physical length of the lens is shorter than the focal length.

Retro Focus
A wide-angle lens design that uses an inverted telephoto configuration.

Quasi fisheye
Produces an image that covers the entire frame.

Fisheye
A wide-angle lens with an angle of view exceeding 100 degrees.

Catadiptric / mirror lens
A lens where the light bending is done with mirrors rather than lenses.


Supplementary / close up
Used in front of the camera lens to enable it to focus at close range.

Macro
A lens that allows a camera to focus at very close range to photograph small objects.

Teleconverter
A secondary lens which is mounted between the camera and lense to increase the focal length.

PC / tilt shift
A perspective control lens allows the photographer to control the appearance of perspective in the image.

Lenses

Convergent (positive,double convex) and Dirvergent (negative, double concave) lenses

http://www.physics.uiowa.edu/


Angle of incidence and refraction

https://www.e-education.psu.edu/


Correct viewing distance of an image

VD = F x M

F = focal length
M = magnification

Notes

Ideal Shutter
-expose each part of the sensor equally and simultaneously
-be silent in operation
-vibration free
-little effort to set in motion
-take minimal time to open and close

Between the Lense (BTL) or Leaf shutter
-operates between lense elements
-must be 'cocked' during lense attachment/removal
-max speed of 500th due to mechanical limitations
-syncs with electronic flash at all speeds

Depth of field
The region of acceptably sharp focus around a subject position, extending toward the camera and away from it, from the plane of sharpest focus.
The boundaries of depth of field are refered to as the rear limit(d1) and far limit (d2)

Increasing depth of field
-smaller aperture - greater depth of field
-larger subject distance
-use wide angle lense

Automatic diaphragm
-stays open until shit is taken
-diaphragm closes down to present aperture

Hyperfocal distance
Focus a lens at the hyperfocal distance and everything in the photograph from some near distance to infinity will be sharp. Landscape photographs are often taken with the lens focused at the hyperfocal distance; near and distant objects are sharp in the photos.


Digital capture
uses sensor array types
-CCD (charge coupled device)
-CMOS (complimentary mental oxide semiconductor)

Digital sensor array
-larger size = more photosites = more sesolution
-smaller size = more compact = cheaper
-full frame sensor = 24mm x 36mm
-crop factor relates to the cropping of the angle of view as a result of the smaller sensor
-If noise is consistant then a smaller site will have a lower signal to noise ratio (image quality is affected - ISO is affected)
-small photosite fills - can spill/bleed into adjacent site(blooming)



Dynamic range
-ability of the sensor to record low to high luminances
-SLR = subject luminance range
-known as density range in film
-if photosite overflows it is called 'blooming'

Week Three Overview

Exposure in any given situation depends on:
-ISO (International Standards Organisation) rating
-Subject lighting
-Subject reflectance
-Personal preferance

Doubling of the ISO rating = Double the sensitivity

Eg. ISO200 requires 1/125 @ f8
ISO400 requires 1/250 @ f8 or 1/125 @ f11

High ISO = image degeneration / grain(film) / noise(digital)

Rule of thumb = use the lowest possible ISO in a situation

To prevent camera shake, use a shutter speed that is at least double the value of the focal length.

Intro to Photo Technology Overview

Shutter
- Mechanism to begin and end the exposure
- Shutter types are Focal Plane or Between The Lense(BTL/leaf)
- High light requires shorter exposure, low light requires long exposure

F-Number/F-Stop
- The f-number represents the size of the opening which lets in light
- Large f-number = small apture = less light passed
- Small f-number = large apture = more light passed

Typical range od standard f-numbers
1 1.4 2 2.8 4 5.6 8 11 16 22 32
each step either:
<---doubles or halves--->
the amount of light passed

-Large number = short time = less light passed
-Small number = long time = more light passed

Exposure
-The total amount of light captured
-Exposure = Time x Intensity