https://purengom.com/2008/10/05/dslr%ec%9d%84-%ea%b0%9c%eb%82%98-%ec%86%8c%eb%82%98-%eb%93%a4%ea%b3%a0-%eb%8b%a4%eb%8b%88%eb%8a%94-%eb%82%98%eb%9d%bc/