I just finished coding a (basic) ray tracer in C# for fun and for the learning experience. Now I want to further that learning experience. It seems to me that ray tracing is a prime candidate for parallel processing, which is something I have very little experience in. My question is this: how do I know the optimum number of concurrent processes to run?

My first instinct tells me: it depends on how many cores my processor has, but like I said I'm new to this and I may be neglecting something.