Practical Screen-craft - 13th October

Tuesday 13th October 2015

Course Module - BAFI101                         Practical Screen-craft                        Lecture - Stu Bailey

Camera control -Exposure Triangle 

If an image is too dark then that means that it is under exposed, known as "crushing the blacks"  and if it is too light then that means that it is over exposed, known as "blown out". 

3 main controls in the exposure triangle 

Shutter Speed - Creates motion and blur for the image - important to use a set shutter speed of 1/50= 50 - standard is 25fps so x2 to get 50 but then if you want slow motion you can do 50fps x2 to get 100fps. Adjusting the exposure of an image doesn't need to use the shutter of the camera. 

Going down makes our image look lighter, going up makes it look darker, increasing everything will make the picture look fake, unrealistic which can look awesome for films like horror and SCI FI. 

ISO - ISO is the sensitivity of the camera, standard ISO 100 - 400 lower the iso the slower the filming speed. Iso within the Cannon 600D's is only usable up to 1600 as after that the image will start to deteriorate and become grainy. Even using 1600 ISO can give you some of that grain which could create noise on your image, doesn't look great, better to have a nice clean image. Always make sure to set your ISO before you start shooting. 

Aperture - Predominantly this is the main way to control exposure and light into the camera - Hole in the lens of the camera, know as the iris which is the mechanism that controls the whole for the aperture. 

Term used - F stops - There are a set range of F-stops in each camera which will give you a different sized whole. However, we have to be aware that the numbers are the reverse to the aperture. 

F2, F2.8, F4, F5.6, F8, F11, F16, F22 - Stopping down on these will half the amount of light that the camera is letting in, opening up will obviously increase the amount of light that is being let in to the camera - Not all lenses will open to the same amount, 

Example of a slow lens - Cannon 600D which has an F-stop of 3.5 
Example of a fast lens - 1.5 F-stop 

The brighter the aperture, the shallower the depth of field. Depth of field is the term used when we describe whats in focus from the front of the camera to the back of the lens. The better the lens, means more aperture which will give a shallower depth of field. 

Always a great idea to under expose your image as you can bring up the colours of the foreground in post production i.e. editing.

If an image is dark, you will need to add light but if an image is light then you will want to use something known as an ND filter, known as a neutral density filter which you put onto the end of the lens. You can get a full frame ND filter or you can get a variable ND filter but in most video camera's such as the Canon XF100's that we are using, they have ND built into them so video cameras are much more setup as oppose to DSLR cameras.