Sony ILCA-77M2 - Manual (Page 37)

When changing the lens, work quickly in a dust-free location to keep dust or debris from getting
inside the camera.
When shooting, remove the front lens cap from the front of the lens.
2. Mount the lens by aligning the two orange index marks (mounting indexes) on the lens and camera.
Hold the camera with the lens facing down to prevent dust and debris from entering the camera.
3. While pushing the lens lightly toward the camera, turn the lens slowly in the direction of the arrow
until it clicks into the locked position.
Be sure to hold the lens straight when attaching it.
Note
Do not press the lens release button when attaching a lens.
Do not use force when attaching a lens.
E-mount lenses are not compatible with this camera.
When you use a lens with a tripod socket, attach a tripod to the tripod socket of the lens to help
balance the weight of the lens.