Testing the Cepheid P-L relation using optical and K-band imaging

We present here preliminary results on main sequence fitting to seven Galactic open clusters containing at least one Cepheid. The reddening towards these clusters is estimated from U - B:B - V colour-colour diagrams and the distance is estimated using main sequence fitting of the V:V - K colour-magnitude diagram. We find difficulties in fitting the U - B:B - V diagram to two of the clusters and suggest this could be due to the effects of metallicity. An attempt to include any effects this would cause to the Cepheid Period-Luminosity relation zero point has been made. The preliminary distance modulus to the LMC obtained from this work is then 18.7+/-0.15.