I want to use accurate caustic with motion blur.

[kiyeol_paek]

hello. I am making a car driving scene with Vray.

The camera is moving along with the car, and I want to create a caustic effect where the sunlight reflects off the wheels on the car.

However, contrary to expectations, the caustic is expressed blurred and with motion blur applied.

I hope the caustic is expressed realistically, like the attached corona rendering image.

Is there a way to set it up separately in vray?

[kosso_olli]

hello. I am making a car driving scene with Vray.

The camera is moving along with the car, and I want to create a caustic effect where the sunlight reflects off the wheels on the car.

However, contrary to expectations, the caustic is expressed blurred and with motion blur applied.

I hope the caustic is expressed realistically, like the attached corona rendering image.

Is there a way to set it up separately in vray?

Well, in the Corona example the caustics of the wheel are blurred as well. And they have to be.

[fixeighted]

I tried this this morning and couldn't get the caustics to remain sharp. I mean on the non spinning wheel parts.
Is this the fact that Corona has it working but Vray doesn't?

[kiyeol_paek]

Well, in the Corona example the caustics of the wheel are blurred as well. And they have to be.

I think I explained it too poorly.
Blurred caustics is not limited to wheels.
As the camera and car move together, the car appears clearly, but the caustic reflections on the floor (body, wheels, chrome, etc.) appear as motion blur depending on the direction of the car. It seems as if only the caustic has stopped in place.
Even if you connect sunlight to the camera movement path, the result is the same.

[Joelaff]

I think you guys are agreeing…

The caustics from the car on the ground (assuming flat ground) should be sharp because there is no motion relative to camera raster.

However, the caustics from the wheels are generated by a moving object (wheel) and therefore do have rotational velocity relative to the camera raster (film plane). So the caustics made by the wheels themselves should be blurred.

[fixeighted]

Yeah that's the case. The example is from a 6 year old page bigging up Corona, which is quite funny https://www.chaos.com/blog/what-are-...-the-right-way
Vray however cannot do this, which seems odd and of course a shame. Why it blurs the caustics is a mystery which may remain unanswered