Barnack conceived the Leica as a small camera that produced a small negative. To make large photos by enlargement, (the "small negative, large picture" concept) requires that the camera have high quality lenses that could create well-defined negatives. Barnack tried a Zeiss Tessar on his early prototype camera, but because the Tessar was designed for the 18×24 mm cine format, it inadequately covered the Leica's 24×36mm negative. Barnack resorted to a Leitz Mikro-Summar 1:4.5/42 mm lens for the prototype, but to achieve resolution necessary for satisfactory enlargement, the 24x36 mm format needed a lens designed specially for it. The first Leica lens was a 50 mm design based on the Cooke triplet of 1893, adapted by Max Berek at Leitz. The lens has five elements in three groups—the third group being three cemented elements—and was initially named the Leitz Anastigmat. Unlike other triplets, the Leitz Anastigmat has the diaphragm between the first and second elements. When the Leica was first vended, this lens was renamed the ELMAX, for E Leitz and MAX Berek. By 1925, the Leitz laboratories had produced glasses with improved optical properties, and Professor Berek designed an improved version of the ELMAX named the ELMAR that had four elements in three groups. The third group was simplified to two cemented elements, which was easier and cheaper to make. Professor Berek had two dogs, Hektor and Rex. The first of these, Hektor, gave his name to a series of Leica lenses, and the name of the second appeared in the SummaREX.