The main sequence from F to K stars of the solar neighbourhood in SDSS colours

For an understanding of Galactic stellar populations in the SDSS filter system well defined stellar samples are needed. The nearby stars provide a complete stellar sample representative for the thin disc population. We compare the filter transformations of different authors applied to the main sequence stars from F to K dwarfs to SDSS filter system and discuss the properties of the main sequence. The location of the mean main sequence in colour-magnitude diagrams is very sensitive to systematic differences in the filter transformation. A comparison with fiducial sequences of star clusters observed in g',r',i' show good agreement. Theoretical isochrones from Padua and from Dartmouth have still some problems especially in (r-i)-colour.