Today’s Question: Why would a mirrorless camera have an option to use a mechanical shutter that reduces the frame rate?
Tim’s Quick Answer: A mechanical shutter ensures you will not end up with visual artifacts in photos that include movement in the scene, which can result from a completely digital shutter with the image sensors in most digital cameras.
More Detail: The image sensors in most digital cameras use what is often referred to as a “rolling shutter”. Rather than the entire image sensor being recorded at one time, the sensor values are read row by row. With very fast-moving subjects in a scene you are photographing, this can lead to visible artifacts or aberrations in the image.
For example, if you capture a photo of the spinning propeller of an airplane using an electronic shutter, you will often see that the propeller appears to have several pieces that are floating, not appearing connected to the actual propeller blades.
There are, of course, some advantages to an electronic shutter. You can generally achieve a much faster shutter speed with an electronic shutter compared to a mechanical shutter. You can also (as noted in today’s question) achieve a faster frame rate with an electronic shutter compared to a mechanical shutter. An electronic shutter can also be completely silent, which is not possible for a mechanical shutter.
In other words, there are benefits to both types of shutters, depending on the situation. This is the reason some cameras that feature an electronic shutter will also include a mechanical shutter. This enables you to switch between the two options depending on the specific needs for the scene or subject you are photographing.