Here's pictures of Black spot on roses, very similar to what you can experience of camillias... the article suggest sulphur compounds to combat the malady. We've had good luck with a product called Dormant Oil which you mix with water and spray on the plants... very smelly, but works great! http://www.extension.umn.edu/distribution/hort iculture/DG1163.html
Thanks for taking the trouble to show everything. Unfortunately, it does not resemble blackspot nor does it cause the leaves to drop. IOt truly looks like someone has spread soot on some of the leaves. Maybe a form of mildew?
I think that you've done it. Sooty mold looks about right. As to trying the home made solution, I think that I will try my local garden center first to see what delights they can come up with to ride my plants of this dreaded lurge.
Thanks for all the effort.