Optics



Exposure Triangle

Exposure is based on three elements that interact with each other. These three elements are SHUTTER SPEED, APERTURE and ISO RATING (sensor sensitivity) and can be demonstrated in a triangle, the "Exposure Triangle".

Within the triangle different settings of these three elements can be combined to get a correct exposure for photo or video.
With shutter speed it is decided whether we want to freeze an action or show movement, with aperture it is decided whether we want a shallow depth of field or have everything in focus and with the sensor sensitivity or ISO setting the noise is higher or lower.

Shutter Speed (exposure time) - Aperture (opening) - ISO (noise)

A higher shutter speed (shorter opening time to expose) needs a smaller f/-number (larger aperture opening) or higher ISO setting (more noise) and vice versa. (By speeding the shutter speed from 1/125 to 1/500 we need to close the aperture opening by 2 full stops.)

A lower ISO setting (less noise) needs also a smaller f/-number (larger aperture opening) or lower shutter speed and vice versa.

A higher f/-number (smaller aperture opening) needs a higher ISO setting (more noise) or a lower shutter speed and vice versa.



Image Sharpness

The optimal range of a lens is the area with the highest sharpness. This range usually starts two F-Stops above the widest opening ( the lowest F-Stop number) and goes to about f/11. For example: a lens with the aperture range of f/1.4 to f/16 the optimal range is the range between f/2.8 to f/11.









Coating

The glass surfaces of lenses are usually coated with a substance that reduces glare and internal reflections.


lens with coating