Schmidt camera optical axis of the Schmidt design creates a Schmidt-Newtonian telescope. The addition of a convex secondary mirror to the Schmidt design directing light through a hole in the primary mirror creates a Schmidt-Cassegrain telescope. The last two designs are popular with telescope manufacturers because they are compact and use simple spherical optics. A short list of notable and/or large aperture Schmidt cameras. Schmidt camera A Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations. The design was invented by Bernhard Schmidt in 1930. Some notable
Adoption of the Gregorian calendar the solar year on a 32-year cycle. Some countries in the Islamic world use the Gregorian calendar for civil purposes, while retaining the Islamic calendar for religious purposes. Saudi Arabia adopted the Gregorian calendar as its civil calendar at the end of 2016. Today, the vast majority of countries use the Gregorian calendar as their sole civil calendar. Countries which have not adopted the Gregorian calendar are Ethiopia (Ethiopian calendar), Iran and Afghanistan (Persian calendar). Some countries use other calendars alongside the Gregorian calendar, including India (Indian national calendar), Bangladesh (Bengali calendar), Nepal (Vikram Samvat), Pakistan (Islamic calendar), Israel (Hebrew