Required for astrophotography and imaging exposures longer than about 5 minutes. The Equatorial Wedge is mounted between a telescope and the tripod to accomplish the tilt of an equatorial type mount that matches the observer's latitude and permits precise polar alignment of your telescope. The wedge allows the astrophotographer to align the telescope's axis of rotation with the Earth's axis of rotation. This alignment eliminates stars in your long exposure photograph from appearing as a long arc, trail or streak due to an effect known as field rotation. For images under approximately 5 minutes a wedge is not necessary.