Photography

Question 1

Photography in forensic science

Answer 1

Scenes of crime
- could be only record of the scene
- remind scientist ins and out of scene
- show relationship between objects in court
Laboratory
- document the exhibit
- evidence that items have been correctly handled and packaging is intact
- document a process
- image analysis

Question 2

types of cameras

Answer 2

• range finder
• mirrorless/MILC
• point and shoot
• twin lens reflex
• plate or view camera
• single lens reflex (SLR)
• twins lens reflex

Question 3

mobile phone

Answer 3

• a phone camera module has to be very small, this means compromises
• a true camera will always outperform a mobile phone

Question 4

SLR cameras

Answer 4

control and flexibility
- interchangeable lenses
quality
- SLRs are the choice by pros although mirrorless cameras are becoming accepted too
functionality
- because the view is essentially through the lens there are no parallax issues
many accessories available - remote shutter releases, GPS units, flash etc

Question 5

Interchangeable lenses

Answer 5

lenses are generally defined by their

• focal length
• maximum aperture
• what other ‘features’ they possess

Question 6

the camera lens- what does it actually do?

Answer 6

• beams of light reflect from the scene enter the lens where they are redirected to form an image
• camera lenses are converging
• objects closer to the lens appear larger and objects further away look smaller on the final image
• the further the object gets from the lens the less the light must bent to become focussed

Question 7

how do lenses work

Answer 7

focussing

• a mechanism which allows the lens elements to move backwards and forwards in the lens barrel so the photographer can select what should be in focus
• can be done with autofocus or manually

Question 8

the focal length

Answer 8

the distance between the point of convergence and the sensor
- smaller focal lengths (16-28mm) are known as wide angle lenses have a wide field of view 84-55 degrees- useful for images in tight spaces

• normal lens (35mm) approximate the view seen though the human eye with a field view of 45 dgerees- standard lens
• a short telephoto or portrait lens (50-90mm) is great for flattering images of people with a field of view of 32-18 dgrees
• longer focal length lenses (90-40mm) are often called telephoto lenses and enabling imaging of far off objects- field view of 18-4 degrees great for paparazzi etc
• ultra wide (8-15mm) or even fisheye which may have a field of view over 180 degrees

Question 9

the normal lens

Answer 9

• focal length equivalent to human vision
• 35mm focal length ( FX sensors has focal length 50mm)
• try using this focal length as it is most realistic

Question 10

the problem with

Answer 10

wide angle lenses
- distort the image
- may have enormous depth of field so may be impossible to get out of focus background or foreground
telephoto lenses
- tend to make the image look rather ‘flat’
- little depth of field
- have smaller maximum apertures hence less light so longer shutter times

Question 11

the zoom lens

Answer 11

• a lens which allows a range of focal lengths
• the zoom lens can be set to fill the image with the subject
• they may perform less well than prime lenses
• they also unlikely to offer large maximum apertures which means they may not perform well in low level lights

Question 12

specialist lens

Answer 12

MAcro lens

• allows user to get extremely close to the subject
• valuable for imaging small objects such as cartridges, bullets, pellets etc

Question 13

specialist lens

Answer 13

perspective control or tilt shift lens

• ensures vertical lines are vertical
• wide angle lens may cause lines to converge- Called perspective projection distortion
• happens when camera is not parallel