Any theoretic reference available for transformation coefficients?

Hello all,

this month I am performing transformation coefficinets computing for my optical system+filters+camera, using M67 field.

Thanks to several articles, specially the one by Gordon Sarty, I learned on how to compute coefficients from instrumental magnitudes and standard values provided by Henden. I think I have all clear about the procedure.

But now, even Sarty's paper makes an introduction about trasformations, I cannot get a complete comprehension of transformation principles: why there are a certain number of band coefficients, and one another of color coefficients? Is transformation taking into account the difference in response between real filter and the Kron-Bessell-Cousins specification altogether with optical system transmision and ccd's quantum efficiency? and more questions.....

Is there a theoretical source about transformations available?

Thanks.

Miguel