Lecture 5 Flashcards
What is exposure for still photography and cinema?
recording images of subjects to photo (light) sensitive film or digital media via photo sensor through controlled exposure of the subjects to ambient or / and additional light.
What five main factors control and affect exposure in cinema?
Aperture Shutter ISO Filters Light
List the available light sources to consider when setting exposure?
Sunlight Moonlight Street lighting Interior lighting Car headlights Electronic lighting Candlelight and flame
What is available ambiance light?
Natural or synthetic light present in the scene location
Name two sources of natural light.
Sunlight
Moonlight
Explain the additional light source film lighting?
Film lighting -mains/battery powered lighting on stands/clamps
Explain the additional light source ‘practicals’
Lights in normal domestic/ commercial light fitting on ceilings/walls/table lamps etc
What are mixed light sources?
Natural light
Ambient synthetic light
Additional film lighting
Colour temperature
5,000 / 6,000 = daylight
As it goes down it gets warmer and as it goes up colder.
Measured in kelvin
Note that the colour of the day with impact the ambient light
What is the colour temperature of candle light?
1,850 -1,930 k
What is the colour temperature of electronic flash?
5,500 k
What is the colour temperature of blue sky, sunlight?
10,000 k
What is the colour temperature of early morning/evening?
3,500 k
What is the colour temp of sunrise/sunset?
2,000-3,000
Colour temperature of mid morning/afternoon?
4,500k
Colour temperature of late morning/early afternoon?
5,000k
Colour temperature of average noon?
5,300 - 5,500 k
Shade or cloud colour temperature is …?
Anything between 6,000 - 8,000k depending on the clarity of the day
How do you set the white balance on a black magic camera?
Set from choosing from a list of kelvin settings such as 5600k
What is alternative method to establish a white balance?
In many video cameras it involves the use of a push-button control, along its white card/paper places between the main light source and the subject.
How can you manipulate manual white balance settings?
Deliberately creating a warmer (yellow/orange) or colder (blue) than reality can be done by using coloured card for the manual white balance set.
Blue card - warmer as camera tries to neutralise the tint and render it white.
Yellow/ orange - colder as the camera tried to neutralise and render is as white.
Shutter in terms of exposure for cinema
Is expressed in speed (normally approximately 50th second) or angle (normally 180•)
• = degrees
Why is recording moving images using shutter speed limited? List two reasons:
- Restricted by the need to acquire a number of frames per second to produce ‘moving’ images. E.g 24/25 frames for cinema for tv
You can’t have a shutter below 30th second to get 24/25 frames per second. - Faster shutter speeds (over 2 x the frame rate/ f.p.s affect the impression of natural motion.
If light is reduced there will be A reduced amount of motion blur making it seem unrealistic.
What is the frame rate for natural movement?
24fps or 25fps
What is the rule to abide by when choosing shutter speed and keeping motion blur?
Choose a shutter speed twice the frame rate
So 25 FPS needs 50th second shutter speed = 180• shutter angle.
What is the effect of Setting a faster shutter speed or shutter angle?
The images sharper but the motion appears less smooth due to the lack of motion blur.
50th or 60th second are not normally used but can be interesting
At 180• shutter angle what is the shutter speed for 24 FPS
24 FPS is 1/48 sec
25 FPS is 1/50
At 90• for 24 FPS
24 FPS 1/96 sec
25 FPS 1/100
45• for 24 FPS
24 FPS 1/192 sec
25 FPS 1/200
22• for 24 FPS
24 FPS is 1/384 sec
25 FPS 1/400
This is where the standard aperture stops so choosing a faster speed/ angle requires exposure compensation such as opening aperture
What is aperture for cinema?
Aperture ‘iris’ contributes to controlling exposure. Doubling or halving the light passing through the shutter as f stops are opened up/closed down but exposure can be regarded as the secondary function of aperture.
What is apertures primary function?
Capturing the motion picture image should controlling the depth of field - depth of focus.
In motion picture cameras the shutter speed /angle is restricted so exposure is balanced with other elements and methods of exposure control.
At any shutter speed changing the aperture to achieve the desired depth of field may result in over or under exposure… how can this be rebalenced?
Neutral density filters
Lighting
ISO setting
Shutter speed
What is a natural density filter? (ND)
Colour - neutral (grey scale) filters used to reduce expose (darken image) in order to compensate for the aperture to be opened up, which increases the exposed when seeking the shallow depth of field.
ND filters may be internal (camera switch)
Or attached via a filter ring or matt box
What may be needed if the aperture is closed down to achieve a deeper depth of field and the exposure is reduced so the image is darker?
Additional lighting - to correct the exposer by increasing the overall illumination.
ISO means?
Light sensitivity setting
What does increasing the ISO light sensitivity eventually do?
Noise/ grain that becomes visible but when it becomes visible can vary according to camera/ sensor type.
1600 is usually when noise begins to be noticeable
What is the native ISO for black magic camera or BMPCC?
800 ISO
If unfamiliar with equipment and use auto manual exposure what are the priority’s?
- Exposure of subjects face
- Avoid exposure altering as the light levels change
Solution for this is to see exposure lock
Method for using exposure lock:
- Auto meter critical area such as face.
- Press exposure lock button
- Reframe and shoot - exposure remains locked even when the camera moves and light levels change until reset.
What is dynamic range?
Dynamic range is the ability of the camera to render accurate exposure of entire image from shadows through mid-times to highlights without crushing blacks or clipping whites.
What to cine lenses differ from photography lenses?
De-clicked aperture ring - allowing alterations of exposure during shoot.
T stops instead of f stops - more accurate light transmission
What is FPS
Frames per Second
Or frame rate
Does frame rate determine exposure?
No, not by itself
Does the frame impact exposure in any way?
Yes, the number of frames per second limits the selectable shutter speed / angle
In particular it’s harder to use slower shutter rates.
Fast shutters can be used easily with aperture and iso whereas slow can’t be much longer than twice a frame rate which is usually 50/180•
What does frame rate do if it does not determine exposure?
Frame rate determines the characteristics/ quality of motion.
How many FPS does the films in the cinema use?
24
Why 24 FPS
24 FPS is the running speed at which the effect of motion created by Film frames running through the projected convincingly smooth enough to represent real movement.
What would a FPS of 16 -18, like they did in early Cinema, do?
The movement was jerky and uneven
How many frames per second do tv programs typically run at?
25 - uk/Europe
30 - USA
How many FBS does online video run at?
30/25 FPS
What effect is created when camera frame rate differs from projector frame rate?
Camera 100 FPS; projector 25 FPS = slow motion
Camera 15 FPS; projector 25 fps =
Fast motion
