How Do You Calculate E(B-V) for Correcting Reddening in Globular Cluster M5?

[taylrl2]

I am currently writing up a photometric analysis of globular cluster M5 which I am doing from a set of images i have taken in the B,V and R bands. The CMD i have produced is obviously too red and faint due to the effects of extinction and reddening. As I am trying to calculate a distance using the luminosity of the tip of the RGB this effect is quite crucial. I know its E(B-V) that i need to calculate but i can't for the life of me think how to do it, any ideas? Thanks

 

[turin]

Do you know the theoretical ratios of E(R), E(B), and E(V) that you should expect without extinction?