What is the role of the 45-degree mirror in a DSLR camera?

The role of the 45-degree mirror in a DSLR camera is to convey the image to the sensor. In a DSLR, light from the lens first strikes the 45-degree mirror, which reflects the image up into the optical viewfinder through a series of additional mirrors and prisms. This setup allows the photographer to see exactly what the lens sees in real time, providing an optical view that is not affected by any electronic processing or delays.

When the shutter button is pressed, the mirror flips up, allowing light to pass directly to the image sensor, which captures the photo. This mechanism is what differentiates DSLRs from mirrorless cameras, where light passes directly to the sensor without the need for a mirror system. The 45-degree angle of the mirror is crucial for directing the light path within the camera, ensuring the user can have an optical viewfinder experience that is clear and direct.