Camera vibrations caused by mirror movement can reduce sharpness. The effect is the more noticeable the longer the exposure time becomes. To reduce these vibrations use live view or exposure delay mode.
Single-lens reflex (SLR) cameras use a mirror to deflect the light into the viewfinder. This mirror obscures the sensor and therefore must be lifted before the camera can take an exposure. The lifting of the mirror causes the camera to vibrate slightly, even if the camera is mounted on a tripod1.
In live view mode the camera does not use the viewfinder at all and the mirror will be locked in the up position. This mode, when implemented correctly2, can greatly reduce camera vibrations.
Another advantage of live view ist that you can attach a HDMI monitor to your camera and preview the picture on a big screen.
Exposure Delay Mode¶
Use this mode is live view is not available or broken. This mode waits 1 second after lifting the mirror and before actually taking the picture. Most of the vibration has damped by then.
Exposure delay mode does incur a speed penalty but this penalty is less than one second per exposure because you must subtract the time it takes the camera to write the picture to the memory card.
Mirrorless Interchangeable-Lens Cameras (MILC) do not have a mirror and thus are for RTI imaging a suitable alternative to the more common (as of 2018) SLR type. The lenses for MILC cameras are not compatible with SLR type lenses and being comparatively new the choice of lenses is more limited (but there are adapters).