The route that light follows through a DSLR camera (or any optical system) is called the ‘Optical Path’. In the case of a DSLR, light can take one of two routes…
- During exposure: light goes directly through the lens and strikes the digital image sensor.
- During scene observation: light through the lens is reflected along a complex path to the eye.
For the passage of light through the lens the optical path is coincident with the optical axis. However, the optical path may differ from the optical axis after passing through the lens if it is reflected to the eye bypassing the image sensor.