Week 8

Maximum Lens Aperture
- how big the hole/aperture can go
- biggest hole in the diaphram
what does 1:1.4 indicate?
ration= max aperture diameter: lens focal length
eg: if lens focal length= 50mm
maximum diameter=35.7mm

Relative lens aperture
focal length 35mm
max aperture f2
max aperture diameter 175mm
focal length 105mm
m.a f2
m.a.d 52.5mm
f2 on 25mm ad of 12.5
f2 on 50mm ad of 25mm
f2 on 100mm a.d of 50mm

Aberation 'n' stuff
an optional error
no lens is perfect
can be corrected by introducing alternative errors in lens
some errors are welcomed- soft focus lens

Why do aberrations exist?
- light is bent ir refracted as it passes through glass
- spherical surfaces fail to bring light to a focus.
-most lens elements have spherica surface
-lenses cannot bring marginal and axial rays to same point light from edge focuses -nearer lens
-loss of contrast
-stopping down can reduce this abbertaion
-can be reduced by delibertaion use of other aberrations
-can be reduced by deliberate use of other aberrations

Achromatic, corrected for 2, blue and green
Apochromatic, corrected for 3, blue, green and red.
--
colours focusing at different distances leads to blurring with symmetrical colour fringing
coma (not cooma)

Lens Aberration Test.

For this assignmnet i used my 18mm- 55mm lens

18mm



24mm



35mm




55mm




Chromatic Aberration



There is a light bend in the guttering of the roof while the lens zoom was set on 18mm and 24mm. When i zoomed in a little more up to 35mm and 55mm the aberration is barely visable.

Week 7

Digital sensor array- does size matter???
Yes and no
Larger size=more photosites=more resolution
Smaller size=more compact=cheaper
1.35mm film size
Film is 35mm wide
Image area=24mm x 36mm
Half frame compact cameras=24mm x 18mm (circa 1913)

Sensor array size
Full frame sensor=24mm x 36mm
Smaller sensors defined with a crop factor
Eg: 1.5x
1.6x
crop factor relates to the cropping of the angle of view as a result of the sensor.
Effective focal length of lens is magnified by crop factor
Eg: 200mm lens x 1.5=300mm(effectively)
Photosite size and noise
SLR= Subject Luminance range
Film: known as “density range”
If photsite overflows it called “blooming”
Ability of sensor to record low to high luminance’s

Tungsten lighting
Electricity passes through tungsten filament causing it to glow, more electricity=more light
Tungsten filament lamps
Tungsten discharge lamps

Week 6

Hyperfocal distance
Lens focused at infinity d1 for any given aperture is known as H.P
Lose half of your d.o.f if lens is on infinity

Sensor array type- differences
CCD
-separate off sensor signal amplifies, often just one result in: less noise, more uniform output, slower to analyse and amplify signal
-more “photosites” in a given area
-uses more power
-more expensive to manufacture.

CMOS
-signal amplifier at each “photosite” results in- more noise, less uniform output, faster to analyse and amplify signal
- fewer “photosites” in a given area
-uses less power
less expensive to manufacture
advances have preferred sensor type

Week 5

The ideal shutter should
Expose each part of the film/sensor equally and simutanlesly
Be silent inopertaion
Be vibration free
Little effort to set in motion
Take minimal time to open and close
Effective exposure should be repeatable

Focal plane (FP) shutter
Flash should only operate when shutter is fully open
Flash synchronisation is therefore limited
In order to achieve very fast speed the 2nd curtain is released soon after the first to follow it across the shutter window or “gate” as a “slit”

Between the lens or leaf shutter
Operates between lens elements
Must be “cocked” during lens attachment/removal
Maximum speed of 500th sec due to mechanical limitations.
Synchronises with electronic flash at all speeds
Most medium format cameras
Accuracy is affected at high shutter speeds and when wide aperture are combined with high shutter speeds eg: 1/500th sec
At 500 a greater proportion of the time is used to open and close the shutter so exposure is actually less than expected.
Often 400 is used, inefficiency reduces exposure closer to that ideal 500th sec
Shutter opens and closes at the same rate regardless of shutter speed chosen
Shorter time to uncover a small aperture
Motion and shutter speed

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 dof are referred to as the near limit (d1) and the far (d2).

Subject distance(u)
Controlling- aperture, lens, shutter speed
Increased- smaller apertures, using larger subject distances, using wider angle lenses

Week 4

Film, shutter speed, lens aperture
ISO400, 500, F8
ISO200, 250, F8
ISO100, 125, F8
ISO50, 60, F8
ISO25, 30, F8

Film, lens aperture, shutter speed
ISO400, F16, 125
ISO200, F11, 125
ISO100, F8 , 125
ISO50, F5.6, 125
ISO25, F4, 125

Achieve “correct exposure”.
High ISO= image degredation
Rule of thumb: use lowest ISO in a given situation
Film: increases in image grain
Sensor: increases in image “noise”
Film= fixed sensitivity
Sensors sensitivity can be manipulated
High ISO= high grain
Low ISO= finer grain- portraits
ISO100- finer
ISO3200-grain

Exposure- level of illumination
High- faster shutter speed, smaller lens aperture
Low- slower shutter speed, wider lens apertures
- use of a tripod
hand held work (without vibrant reduction technology)
- use a shutter speed at least twice the value of the lens focal length
eg: lens focal length is 50mm, use at least 100thsec shutter speed


Level of subject reflectance:
-camera uses a reflected exposure meter
-measures light reflected from subject calibrated to always render the subject as a mid tone
-auto or manual results in same rendering
-white subject=mid tone rendering
-mid tone subject=mid tone rendering
-black subject= mid tone rendering

Exposure modes:
-average- entire field of view is averaged
-evaluative- interprets scene based on data base
-centre weighted- majority of measurement in centre
-spot- majority measurement in small area
White wall- 125sec @f9 not 125sec @f22

Week 3

Exposure
total amount of light used to create an image
controlled by shutter speed and lens aperture
1/125sec at f2.8 same amount of exposure as
1000,500,250,125,69,30,15,8,4,2,1 shutter speed (length of exposure)
1,1.4,2, 2.8,4,5.6,8,11,16,22,32 f-number (intensity of exposure)
ISO rating
Subject lighting (level of reflectance)
Your preference
ISO rating
Film with high sensitivity to light has a high rating
Higher the number= greater the light
Film with low sensitivity to light has a lower rating
DIN (Deutches Institut Fur Normung)
ASA (American Standards Association)
ISO (International Standards Organisation)
Eg: Liford HP5> DIN27>ASA 400
Kodak Tmax100> DIN21>ASA 100
Agfrapan25> DIN15>ASA 25
1987: adoption of ISO as standard which uses ASA scale
ISO Standard
A double of the rating= doubling of sensitivity
Eg: ISO400 film is twice as sensitive to light as ISO200 film
Therefore: ISO400 film requires half the exposure as ISO200 film to produce a specific exposure
Assume: ISO200 requires 125 @ f8
Then: ISO400 requires 250 @ f8

Week 2

Aperture
Means hole or opening
Different sized apertures allow exposure to be varied
“Waterhouse stop” – John Waterhouse 1855
Iris diaphragm allows infinitely more control
Term “stop” is still used to refer to a particular setting
Shutter
Mechanism to begin and end exposure/capture
Early versions were simply a lens cap
Low light level requires a long exposure
High light level requires a short exposure
Focal plane or between the lens (BTL/Leaf) variety
Shutter types
Focal point operates in front of the film at the focal plane
BTL/Leaf operates inside the lens much like a diaphragm
Focal plane shutter
2 rubberished cloth curtains, one opens to start the exposure and the second closes to end the exposure
Today, metal blades
Diaphragm, aperture, f-stop, f-number
Diaphragm= mechanism
Aperture= hole/opening
f-stop= particular sized opening
ie; an f-number of 16 is written as f-16 or just f16
f-number=number representing opening
large f-number= small hole= less light passed
small f-number= large aperture= more light passed
typical range of standard f-number
1, 1.4,2, 2.8,4,5.6,8,11,16,22,32
Multiplied by .4
Shutter, shutter release, shutter speed
Shuter=mechanism
Shutter release=the “magic” button
Shutter speed= length of time shutter is open
1/6 sec=60
Large number= short time= less light
Small number= long time= more light
Small number=long time=more light
Typical range of standard shutter speed
1,2,4,8,15,30,60,125,250,500,1000,2000
Each step either double or halves amount
Exposure
Total amount of light captured
Eg: high exposure, low exposure
Exposure= time x intensity
Time= shutter speed
Intensity= aperture size
Shutter speed range
Lens aperture ramge
Exposure range
Exposure modes
ISO range
Preset white/ grey balance
File type

Week 1

Introduction
Camera- (Latin), vault, vaulted room/ small boat
Obscura- (latin), darkness
Camera obscura used as a drawing aid
1265- roger bacon (English philosopher) write about the camera obscura from 10th century arab scholars writings
1490- Leonardo da viinci describes one in detail
1558- Giovanni Battista Della Porta, suggests its use as a drawing aid and then went on to install a mirror and lens to reinvert the image and to make it sharper and brighter
1557- first moveable camera obscura appeared
1685- telephoto lens
Light sensitive materials
There were many significant discoveries from early 1700’s to early 1800’s but history records Joseph Neipce as the person responsible for the first permanent camera image, a view from his window in 1826.
8 hour exposure
Bitumen of Judea on pewter
Camera basics
Light-tight body
Lens of focus the image
Means of capturing the image (film/sensor)
Aperture through which the light passes
Shutter to begin and end the exposure/capture.