Seemingly identical cameras render different exposures

[Fredrik Averpil]

Hi,

I've attached a simplified scene with two cameras which seem identical in the Maya UI... but if you look in the scene file code (MEL), they're not exactly identical. And they don't render the same exposure although I think they should...

Any ideas why this is so?
Could it be a bug?

Scene file:
https://mega.co.nz/#!z8RlEawY!exMTP2...zf9fdQbtuOcF2Q

I'm on nightly build 23395 from Aug 5th, Maya 2012 64-bit, Windows 7 64-bit.

Edit: in a different scene, I cannot duplicate a camera with physical settings without having exposure issues. If I create a completely new camera and apply physical camera attributes, it all seems to work fine. Could it be related?

[Svetlozar Draganov]

The cameras settings are actually not identical in Maya UI as well.
Here are some discrepancies:


When these differences are abolished both cameras produce identical end-result.

Would it be possible to give us step by step instruction of the duplicating camera process - I've run a simple test and both cameras have the exact same appearance.

[Fredrik Averpil]

Hi Svetlozar,

Oh, okay I missed those two attributes. But when I've made sure both camera's resolution gates are set to "fill" and both cameras are renderable, I still get different exposure from the cameras. You say you don't see this difference?

I don't exactly know if the cameras were duplicated and I can't provide a step-by-step... but when I duplicate both cameras and delete the old ones, they still produce different exposures.

When digging deeper I just now noticed what's causing it on my side: center of interest (on the transform node)
- So, if I make sure both cameras have the same center of interest value, both cameras render the same exposure. As soon as a higher value is used, somewhat higher exposure/brightness is applied to the render. As you can see there are very different values to center of interest on the cameras.

Can you reproduce this on your end?

[Svetlozar Draganov]

Yes - the center of interest parameters were also different, I just forgot to mention them.
And yes center of interest parameter affects Exposure settings - so this is probably the main reason for exposure differences.
I think you could avoid such issues if you turn on Focus distance from the VrayPhysicalCamera - then the center of interest won't affect the exposure of the camera.

[Fredrik Averpil]

I see, so this is expected behavior?

I don't understand why center of interest should affect exposure (but I'm sure there's a very clever reason to why it is so).
Enabling Focus distance indeed makes both cameras render the same exposure (brighter rather than darker).

Thanks!

[Svetlozar Draganov]

Center Of Interest represent Camera's Focus Distance.
When Focus Distance in Vray Camera is off - Camera is always focused to the Center Of Interest coordinates.
From the other hand Focus Distance affects the Exposure and that's why sometimes two very similar at first point cameras could produce very different exposures.

[t.petrov]

I see, so this is expected behavior?

I think yes, because in real cameras the exposure changes with the change of the focus distance.

[bigbossfr]

Here :
http://www.chaosgroup.com/forums/vbu...ess#post548882

[Fredrik Averpil]

Would it be a good idea to disable this exposure diff when DOF is not enabled?

[Svetlozar Draganov]

I don't think that this would be a good idea - then the exact opposite issue will appear when you have a camera with already set up exposure/DOF and suddenly you decide to disable DOF for certain frames or for any other reason.

[Fredrik Averpil]

Ah. That's true.

This is a very odd effect. I can't recall ever noticing this when taking photos with my own gear... oh well. At least now we (me and my co-workers) know what's going on...