[Aavso-photometry] Transformation coefficients question

[gianlucaros at gmail.com]

For CCD photometry I currently use a V filter made by Custom
scientific and would like to buy a B filter in order to transform
observations. I was looking at the market and found a B Schuler filter
at substantial reduced price. My questions are:

- is it possible to use the B and V filter effectively given they come
from different manufacturers?

- is it possible to use tranformation coefficients using B and V
filters for differential photometry when there is no reference on
color index of the comparisons stars (I think of the many Mira and
semiregular stars in the AAVSO charts)?

Thank you

Gianluca