Tuesday 26 November 2024
This evening was a practical session run by Kevin, to review the Exposure triangle and specifically Aperture and Depth of Field (Dof).
To get the correct exposure requires the photographer to get the right balance of ISO, Aperture and Shutter Speed and the creative choices are around Shutter Speed and Aperture / Dof.
Kevin began with an explanation of what the f-stop means and why the Aperture gets smaller as the number gets bigger (essentially it’s actually a fraction of f, where f = focal length).
The main creative tool associated with Aperture is the amount of blur (“bokeh”) or detail in the background, with the widest aperture (low f-stop number) creating the greatest amount of bokeh.
Kevin quickly demonstrated how Dof of field works and why depth of field varies with distance of the subject from the camera and the subject from the background, as well as with the focal length of the lens.
(Click on image to make it larger)
Other effects of Aperture were then covered: Starburst at narrower apertures; and the use of Bokeh masks. Then everyone split into groups and carried out various exercises to see the creative uses of Aperture.
Kevin showed three examples of work to demonstrate that the depth of field is a creative choice of the photographer.
Finally Kevin covered three more technical / jargon techniques to exploit aperture when image making, especially using a digital camera:
- Focus stacking – Taking multiple shots of the same scene with different focus points (from near to far). In modern traditional cameras there is often a built in function to perform this task and there are also apps available for Smartphones to focus stack (for example “Open Camera” – Android, “FocusStacker” – iPhone);
- Hyperfocal distance – This is the distance from the camera to focus upon to get everything from near to infinity in focus. There is a complicated formula to calculate this, based on focal length and aperture, but the general rule of thumb is to focus one third of the distance into the image (very useful for landscape photography); and
- Zone focussing – This is beneficial when the subject is relatively close and moving, so that the auto-focus may not work as quickly as the photographer needs. By first focussing on something a known distance away (e.g. 8ft) and using a narrower aperture (f/8 – f/11). Then everything within the Zone (e.g. 6ft to 12ft) with be within the depth of field and therefore in focus. Very useful for Street photography.