I just came across a article about gray cards. The article made perfect sense but I was wondering how it works in reality. So therfore my question: are you using a graycard for setting the whitebalance? If yes, under what circumstances do you recon a graycard as a useful help or even a must? Are these graycards a common thing in photographer's stores or should a order one on the internet? And do you have any tips on how to use them.
Thanks in advance.