Rendering the empty background

[Krisztian Gulyas]

I am rendering an animation of an object now, and there's empty space around it, just the black background, and it takes some time to render that black empty background too. The buckets not just run through that, but stay there for 1-2 seconds. I was wondering why they do that? Is there something that needs to be calculated for example in the upper left corner even though there are no objects or anything else visible?

I haven't noticed this earlier.

max 2014 + vray