Cinematography Study Session

Just a last minute study session.  I typed out everything I could remember about each topic without checking my notes, so here's hoping I've remembered correctly.  Exam starts after lunch today! 


Focal length and Field of View:

The focal length is the distance between the center of lens and the sensor.  Camera lens lengths are usually specified in mm.

The Field of View refers to the extent of the observable world that can be seen at any given moment.  In this case- how much can be seen in frame, or how much the camera captures.

Field of view is connected to focal length through angle of view.  A smaller focal length results in a wider angle of view.  This then results in a larger field of view. 

If the focal length is changed the angle of view also changes, resulting in a different field of view. 

Kelvin Scale and Colour Temperature:

The Kelvin scale was created by Sir William Thomson.  It uses a scale from absolute zero- which Thomson defined as the point where molecules stop moving.  In his experiments Thomson heated carbon and watched as the colour changed from red to white-blue at it's highest temperature.

This is why the hottest temperatures on the kelvin scale are sky blue at 10000K.

In cinematography Kelvin is used for lighting and determining the colour temperature.

It is typically used in white balancing, which determines the overall temperature of an image, and allows the camera to identify colours correctly.  If footage looks too yellow then the White Balance temp is too high.  Colour temperature can be manipulated to alter the mood of the film. 

Principles of Shutter:

One type of shutter is the rotary shutter, which is found in film cameras.  Rotary shutters have a disk which rotates in front of the film gate to allow the film to be exposed.  Some rotary shutters allow the shape of the shutter to be altered.  This is called the shutter angle.  The standard shutter angle is 180°.  Changing the shutter angle will cause different effects on your footage.  A smaller shutter angle: eg 90° will have less motion blur and result is a sharper image.  It will also allow less light to enter the lens effecting the exposure of the film.  As the angle decreases further is will give the footage a stuttery, stop-motion look.

In digital film a shutter angle of 180°= a shutter speed of 1/50.  Shutter speed refers to how long the frame is exposed for.  A standard rule of thumb is that the shutter speed should equal twice the FPS, but this can also be altered for different effects.  A faster shutter speed eg 1/30 will result crisp, choppy footage with reduced motion blur, while a slow shutter speed (1/400) will result in a less sharp image, with lots of motion blur and smoother motion.  As with shutter angle, shutter speed also affects the exposure of the film, with longer shutter speeds make the footage more exposed.

Aperture:

Aperture is the hole in the lens which lets the light through.  It refers to how open the lens of the camera is, and is represented in F-Stops.  The smaller the F-Stop (Eg F1.4) the larger the aperture.

A small F-Stop allows more light to enter the camera resulting in a smaller depth of field, less overall sharpness and a more exposed image.  Opening the Lens by 1 F-stop doubles the amount of light that goes through.  Reducing the F-Stop by 1 halves the amount of light.

Disadvantage of a very small aperture= a decrease in sharpness because of diffraction.
Disadvantage of a very large aperture= Distortions, Chromatic Aberrations, Optical Vignetting  

Different lens don't allow the same amount of light through even if they have the same F-Stop.  T-Stops measure the amount of light going through a lens.  T=F/ Lens Transmittance %.


Inverse Square Law:

Inverse Square law states that a physical quantity or strength is inversely proportional to the distance from the source.

In cinematography this relates to the relationship between the intensity of the illumination of a subject and their distance from the light.

I= 1/D²

If the distance between the light and subject is double the intensity will be 1/4 of the original.  A 2 stop loss of intensity will occur every time the distance is doubled. 

An example: If the light in it's initial position is one meter from the subject then its intensity is at its most powerful. If it is moved 1 meter further back distance=2. 1/2² = 1/4= 1/4 loss in intensity.  Of the light is moved another meter distance=3. 1/3²= 9= 1/9= 1/9 loss in intensity.

Lux and Illuminance: 

Lux is SI unit of Illuminance.  It can be measured using a light meter but these mostly use foot-candles instead.  I can't remember much more off the top of my head about it, so I will want to avoid this topic in the exam.