Vray camera exposure wrong only when rendering animation

[stefanfahrngruber]

Hi there,

 

I'm currently working on a project and have some difficulties with Vray Camera. (3Ds max 2012)

 

It's a technical vis in a small scale (a few cm). Exposure is adjusted fine. To show a detail I have to zoom in and out. While zooming in the exposure goes down (which seems plausibel as less light from the scene hits my sensor).

 

To have the exposure correct while zoomed in I animated the ISO. (not the best way but as it's a technical demo I don't want more dof or what ever, everything just should stay the same)

 

Now for the strange part. bevore rendering the whole movie I made a few testframes. All perfectly exposed.

 

But when I render the whole animation (every frame) the exposure around the Zoom goes way off (too bright). Some times the images get brighter even before the actual zoom (and there fore the isochange) takes place.

 

I tried to use a Moviecam and a Stillcam. No exposurecontroll or from Vray camera (which works out the same). Also tryed to use a linear and smooth curve on the animated ISO.

I use of course Singleframe mode for GI, because I fade in and move a lot of objects in the scene.

 

The effect only appears with GI on and animated Iso.

 

The thing I really don't get ist why the single frame previews look fine and the animation is off! Even if my GI is set to singleframe mode (isn't it supposed to dump the IR after every frame?)

 

Thankful for any comments,

Stefan

[Chris MacDonald]

Try animating the shutter speed rather than ISO?

[stefanfahrngruber]

Yeah sure, same effect. Anyways it shouldn't matter which one I animate. (changing the shutterspeed would affect my moblur I think which I also wanted to avoid)

[Chris MacDonald]

Ahh, I didn't know you had motion blur enabled.

 

I have no idea what might be causing your problem, other than perhaps cached GI?

[stefanfahrngruber]

I think it has to do with the GI cache too, thought single frame mode should dump it after every frame but seems like it doesn't. Any way to force Vray to dump the GI?

[Chris MacDonald]

Yeah, it recalculates on every frame on single frame mode; so that rules that problem out! Perhaps try it on brute force?

[stefanfahrngruber]

Hi, I will try that, for now I rendered two diffrent clips with each exposure value and fade while the camera zooms in the editing tool not the most elegant way but it works fine.

 

Thanks for your input Chris.

[RyderSK]

Well, your IR gets recalculated, but your LC is still set to flythrough no ? But that's just guessing.

 

Regarding exposure, that's something I would definitely key inside post-production. It will be easier, more precise. All you need is unclamped (or partially clamped if AA is big issue) .exr output. Or I am missing something ?