I've received some questions about the "temporal contrast" option and who stole it from the 3ds max 9 UI.
Here's the deal:
In mental ray 2.1 and earlier, it actually used a temporal contrast, which worked very similar to the overal adaptive sampling contrast. However, this actually yeilds suboptimal motion blur.
So mental ray 3.0 or newer actually takes a fixed number of temporal samples for each spatial sample.
However, the parameter, as exposed in the .mi file format still is "temporal contrast" and is an RGBA color. However, this color isn't actually interpreted neither as a color nor as a contrast at all!
What happens is that a number of temporal samples is calculated from this color as such:
samples = 1.o / min(temporal_contrast)
So this means a "temporal contrast" of 0.2 0.2 0.2 0.2 really only means "5 temporal samples". Nothing else. There is no "contrast" comparisions being done between temporal samples at all!
So... since mental ray does this internally, this was propagated to the max 9 UI as a temporal samples spinner, rather than the old "temporal contrast".
It most likely will be changed in the .mi file format in a future version to a "time samples" instead of "time contrast" keyword.
Hope this is clear as mud... ;)