1. Focus Bracketing enables continuous shooting with the focal distance changed automatically after a single shot

2. 14 Conjugate method is an accurate, simple and convenient method to measure the focal distance of thin convex lens.

3. Provided is a tuyere assembly for a molten iron manufacturing apparatus, which is capable of preventing tuyere damage and reducing the combustion focal distance for higher combustion efficiency of an auxiliary fuel, and minimizing the abrasion of an intake pipe caused by the intake of the auxiliary fuel.