Hello!
There is a strange behavior of camera motion blur, confirmed both in vray 3.7 in max 2020 as well as the latest Vray 5.1.4 in Max 2022. Don’t have access to Next, but it might be the same.
Here’s the story: we are currently working on a automotive commercial, nothing groundbraking, just a couple side views of cars riding fast on a blurred background.
So I thought, no problem, camera motion blur is the way to go. The cameras were parented to the cars, so the speed was matched 100%.
The client expected sharp cars on blurry bg, and so did I.
But then we noticed that at some point in the project the cars were no longer sharp. I did not remember what was the setting I changed, and so I wasted a couple of hours trying to find the cause.
There are many threads on this forum concerning problems with camera motion blure, but none fixed our problem.
I gave up testing my original scene and made a simple scene with cubes that are moving very fast and some stationary ones (bottom row). The camera is again parented to the moving cubes.
Here are the results:
Going from 5 to 6 geometry samples makes the top cubes (which are stationary in camera space) appear blurred. This was using a Vray Camera. I also found out that with the Physical Camera, the problem begins at 4 geometry samples.
The cubes are more at jet figher plane speed than car speed, but it was noticeable enough even with cars going ~200-300 km/h.
In the attached ZIP file there is a Max 2022 scene. Above renderings are on frame 2. Just up the geometry samples to 6 or more and the problem should appear.
A simple workaround is to control the geometry samples via Vray object properties, but in some cases it might not be a good solution.
Is this a bug, or somehow an expected result?
motion_blur_test.zip (28.1 KB)
