Lecture 4-Essential Camera Operation

Question 1

Why do we aim for optimum exposure?

Answer 1

To maximise quality and strength of the picture signal, ensuring that all illumination levels fit within latitude of the imager.

Question 2

What is latitude measured in?

Answer 2

f-stops

Question 3

What is the latitude of the HPX171 and the Red?

Answer 3

HPX171 about 6 stops

Red about 13.5 stops

Question 4

What happens if bright areas are beyond the latitude of the imager?

Answer 4

All bright areas become a solid white and are clipped.

The specific expose where this happens is called the clipping point.

Question 5

What happens if dark areas are beyond the latitude of the imager?

Answer 5

All dark areas become a solid black and are crushed.

Question 6

What is film exposure referred to?

What does thin and thick negative mean?

Answer 6

Density.
Thin negative: under-exposed.
Thick negative: slightly over-exposed (1/2-2/3 stop)

Question 7

Why do video systems need exact exposure?

Answer 7

Maximise the signal and avoid amplification.

Question 8

Why are digital systems different to film for the optimum exposure?

Answer 8

Shoot to get full distribution of data, very slightly under-exposed (1/2-2/3 stop)

Question 9

Using an HPX171, what range of f-stop could represent full latitude?

Answer 9

F 2.0 to f 16: f 2.8, f 4, f 5.6, f 8, f 11, f 16
All illumination in the scene should fall within 6 f-stops.
A lens’s speed depends on focal length.

Question 10

How do you measure illumination?

Which is the best type to measure for exposure?

Answer 10

Incident light falls onto a subject or area. Reflected light comes from a subject area.
Incident allows overall measurement of illumination independent of the tonality or reflectance of the subject.

Question 11

Describe an incident meter?

Answer 11

Typically have a dome to collect all light falling onto subject. Point centre of dome at middle of camera lens. Calibrated to read for an 18% grey level, at that level incident illumination = reflected illumination.

Question 12

When is measurement of reflected light needed?

Answer 12

When subject is out of reach, when there are specific areas of extreme bright or dark areas.

Question 13

What do spot meters measure?

Answer 13

Enable measurement of reflected light, can convert automatically to an f-stop given other settings typically have a lens to focus on a specific area, often rated in terms of field of view.

Question 14

What is TFTV’s standard meter?

Answer 14

Sekonic 758
Combination incident and reflected light meter
has a 1 degree spot meter built in
Can programme in dynamic range to ensure exposure is within latitude of the camera

Question 15

What is Zebra?

Answer 15

Type of reflected light meter, a simple zone system based on a threshold, commonly found on video and digital cinema cameras. Typically set at a certain IRE (75 for skin, 95 for white)

Question 16

What is false colour mode?

Answer 16

Type of reflected light meter, a zone system based on ranges of luminance, commonly found on digital cinema cameras, multiple zones can be set up and assigned different colours. Purple>black>grey>white>red

Question 17

How can spot meters be used in the same way as incident meters?

Answer 17

Use an 18% grey card at the subject position and measure exposure from it. Cinematographers use both types of systems. You can use zebra or false colour mode in a similar way if you adjust IRE settings.

Question 18

What source does your incident reading measure?

Answer 18

Key source, set your exposure to this, altering slightly as necessary for the particular imager you are using. Ensure that the darkest areas and lightest areas are still within the latitude of your imager, if not use additional light to boost specific areas or find a means to reduce light of overly bright areas.

Question 19

What do you do if the director wants a short DoF but the exposure requires a small aperture? (E.g. F 16)

Answer 19

Use a Neutral density (ND) filter.
Reduces the amount of light entering the lens without affecting colour. HPX171 has ND settings of 1/4 (2 stops), 1/16 (4 stops) and 1/64 (6 stops).

Question 20

You are shooting a scene for a UK TV drama in a house at night. A woman is cowering behind a door trying to hide in a dark room. light is slashing in from the adjacent kitchen. the director wants her to be clearly bur barely visible with a medium DoF so the front part of the kitchen is just in focus. You are shooting with an HPX171 with an 8mm focal length. She is 1m from camera. the important part of the kitchen is 3m away.

What illumination level do you require for the key light?
What should the minimum illumination of the woman be?

Answer 20

1: identified key light source for proper exposure-kitchen
2: determined aperture needed for DoF-f4
3: determined exposure time for format- 1/50 sec
4: calculated illumination level for key- 40fc or 430 lux
5: calculated illumination level needed for her lighting based on latitude of camera - 5fc
Step one: key light source (Kitchen-should be properly exposed)
Step two: Aperture that will give medium DoF (DoF calculator/table)
HPX171 1/3” sensor, CoC is 0.011mm, need to determine hyperfocal distance, f4 is a reasonable guess based on experience.
H= F^2/fxCoC: H=8^2/(4x0.011)=1,455mm=1.46m
ND=(HxS)/H+(S-F). FD=(HxS)/H-(S-F)
ND= (1.46x1)/(1.46+(1-0.008))=0.59m
FD= (1.46x1)/(1.46-(1-0.008))=3.11m
f4 can work
Step 3: exposure time: UK TV PAL-25fps, 1/50th second default exposure time for PAL
Step 4: Illumination required by the key light source to properly expose the scene with f4
Fc=(25xf^2)/(txEI) lux= (269xf^2)/(txEI)
Fc=(25x4^2)/(1/50x500)=40fc
Lux=(269x4^2)/(1/50x500)=430lux
Step 5: calculate the illumination required for her to be barely visible (needs to be within the latitude of the camera.)
Assume the linear processing of light hitting the imager thus the minimum exposure should be at most 3 stops less.
3 stops=1/8 the amount of light
40x1/8=5fc
430x1/8=54lux

Question 21

How do digital imagers and film process light?

Answer 21

Digital imagers- linearly- even distribution between black and white
Film- non-linearly- there is a bias towards lighter and darker tones depending on specific film stock

Question 22

What function in digital imagers mimics a ‘look’ that film has?

Answer 22

Gamma, given an input level gamma alters the output level, thus can add contrast to mid-tones but reduces it in shadow and highlight areas. Display gamma corrects for a source to ensure accurate picture reproduction. Camera gamma enables the imager to react to light in a similar way to film.

Question 23

What are the 4 look parameters in digital imagers to create a film look?

Answer 23

Master pedestal: sets the base black level
Knee: controls the white clipping point (compresses bright areas above a threshold (80-100%)
Matrix: alters colour response (this is different to white balance, films have slight colour bias at different levels of brightness).
Detail affects apparent vertical resolution for progressive.