I am using Iris to do DSLR photometry of V342 Cen.
I have 21 x 30s images of V342 Cen and its comparison stars. I have stacked these in lots of 7 images. I am processing the green channel from each stack. There is general agreement between the resulting green channel images for the instrumental magnitudes of the comparisons and target.
I am using the Reduction Beginners spreadsheet from the Citizen Sky  project.
Do I need to provide a B-V value for V342 Cen itself? Entering a value in the spreadsheet there (i.e. I make one up just to see the results) makes a significant difference to the resulting calculated magnitude for V342 Cen itself. If a B-V value is required, where can I obtain one from? VSX does and the photometry table for V342 Cen do not provide one.
I presume as V342 Cen is a classic CV (UG according to VSX) that B-V will vary with orbital period depending upon which components spectra is dominating - Correct?