An apparatus and method for enhanced gravity casting wherein a portion of the mold is maintained in pressure contact with molten metal as it solidifies to allow the mold surface to follow the contraction of the solidifying metal. The objective lens has a step structure including a plurality of concentrically formed refractive surface zones divided by steps, the step structure having a function of giving, at each step, an optical path length difference of approximately 2\u03bb1 to the first light beam. The tubular shaped spray head is connected to a water source for introducing water in the tubular shaped spray head. The sealing protrusion is formed around the inner surface of the tube. The method further includes performing at each of the peer groups operations on the data. The heart function analysis apparatus includes a strain-value acquisition unit configured to acquire time-series strain values in thickness of a heart muscle from the time-series image data, a normalized strain value calculation unit configured to normalize the time-series strain values, and an output unit configured to output the time-series normalized strain values.