Moving physical camera results in different exposure!?

[Okke]

Hi,

I textured a sphere with an EXR image for background purposes. In that sphere I placed a physical camera. Now when I move my camera closer to the sphere my render gets darker and if I move the camera backwards my image gets brighter. Of course this is not the result I want. I played with some settings and it looks like "exposure color correction" has something to do with it. When I turn off exposure color correction this difference is gone. The only problem now is that my image is white and have to post correct the exposure by -4 to get something decent.

Also I noticed when I turn on DOF my images look much brighter, but this I can compensate with ISO.

Is there a proper work around for this?

Using Maya 2014 and Vray_22501_23192

** EDIT v01**
When I place the camera outside the sphere the problem is gone.

** EDIT v02**
I turned on "compensate exposure" in the vrayMtl as I put the image into self-illumination. This seems to fix it, but now I have to crank down my EXR exposure by 90%. Still hoping to avoid these work arounds.

[vlado]

When you are moving the camera around, I assume you are not moving the center of interest? If so, then turn on the "specify focus" option in the camera and it should be fine.

Best regards,
Vlado

[Okke]

No I use a standard camera without an "aim". I just the camera as a whole.

[vlado]

So did the "specify focus" option help or not?

Best regards,
Vlado

[Okke]

Yes it did Vlado. Thank you for the help

[brainspoon]

We again stumbled accross this problem.
Specify focus will not help with this. Specify focus and center of interest result in the same behavior. The closer those get towards the camera the darker the image will be.
And you will need the focus point to set the depth of field correctly. This will result in changing exposure during animations.

[tashko.zashev]

We again stumbled accross this problem.
Specify focus will not help with this. Specify focus and center of interest result in the same behavior. The closer those get towards the camera the darker the image will be.
And you will need the focus point to set the depth of field correctly. This will result in changing exposure during animations.

Generally this is an expected behavior, but you could send us a part of your scene file to check it out.
You can always disable the camera exposure if you don't need the effect of it.

[brainspoon]

I can't imagine why this is expected. When shooting with my still camera the image does not get darker with different focus distance.

[tashko.zashev]

Hi Brainspoon,

I suppose that you get the effect described in the following topic:
http://forums.chaosgroup.com/showthr...amera+interest

If the case is different with your setup, it will better to check your scene out, because there could be a bug somewhere in the code.

[brainspoon]

Right now I would say it is the same affect. But does it really make sense to make it based on the center of interest? Better would be to just have it influenced by focus distance of the camera or the physical camera.

In Maya during navigation the center of interest changes all the time and having a different exposure in every test render can be really irritating.

[t.petrov]

You can always disable either the physical exposure or you can switch the focus calculation to not use the center of interest, but use a fixed value (see the "specify focus distance" attribute).

[isoparmesan]

This just threw me for a loop. Glad I now know that the center of interest is meant to affect the exposure. However, if "specify focus" is left off, will the center of interest affect DOF as well? It seems very easy to overlook and get confused as there are now 4 potential places to enter a value for focus/exposure distance from the camera (v-ray tab in render settings/cameraShape node center of interest/cameraShape node focus distance/"specify focus" in vrayPhysicalCamera). I was actually completely unaware of the "center of interest" value on the cameraShape, but I normally use a "camera with aim and up" so it gets set automatically. If you use a regular camera it gets set to a arbitrary value as you move the camera.

I can especially see this being an issue for somebody importing a keyframed tracked camera from some match moving software as this is generally a regular camera. In my case the Center of Interest was set to 4 and I adjusted the exposure settings accordingly without knowing that setting affected things. It wasn't until I made a second camera that I started to see a major discrepancy in exposure.

[tashko.zashev]

Hi,

However, if "specify focus" is left off, will the center of interest affect DOF as well?

Yes, camera focus will be taken from the camera aim (Specify focus Off). If you switch it to On, you will be able to control the camera focus field and camera target separately.

get confused as there are now 4 potential places to enter a value for focus/exposure distance from the camera

Yes, there are a lot of options and parameters that allows the user to control the camera, but most of them are overridden by the V-Ray Physical camera.