Then, after the set time of the shutter speed, the second curtain shuts.
When you press the shutter button, the first curtain slides up and lets the light onto the camera sensor. The most common type of shutter has two curtains. Mechanical shutters are found in all DSLRs and most mirrorless cameras today.
Buy from Unavailable Exploring Shutter Actuations: How Does a Mechanical Shutter Work?
