How to set manually a correct Exposure?

[KushKush]

Hello,
Most of my renders seem to have unnatural look, I'm looking to improve my lighting. I'd like to know if there are correct methods to set up photorealistic lighting. For example, if I set a sphere with grey material of 128,128,128, is this the value I'm looking for at the brightest part of the sphere? Or maybe I'm not looking in the right direction? Please help. There are many guides on youtube but I'm yet to find one that talks about the theory behind setting the correct exposure and photorealistic lighting. If Chaos Group has such tutorial, I'd appreciate it if someone can refer me to the tutorial.

[sirio76]

Hello,
I'd like to know if there are correct methods to set up photorealistic lighting

The physical sun/sky is already calibrated, for artificial lights just use a correct luminous flux in lumens and a correct color temperature (you can find these values from manufacturer websites).
Once the light is well calibrated you can use real world value for the camera exposure. There is no correct exposure since light conditions are infinite, be only sure that your exposure gives a balanced result, not too bright and not too dark.
Don't forget about tone mapping, unlike render engines output real cameras output is not in linear multiply, every camera manufacturer tune the results to get a more pleasing look and you should do the same also in Vray.
Here we shared with Chaos some tips including tone mapping (tip 8 )and lighting (tip 5 ): https://www.chaos.com/blog/9-tips-on...ctural-project

[KushKush]

Once the light is well calibrated you can use real world value for the camera exposure.

Thanks for the tips. What does "real world value" means?
I prepared an example that illustrates my question. Two pictures, one is manually exposed (darker picture), and the other is auto exposed by Vray render settings -> Vray camera. The darker one seems for me as more pleasant to the eye, on other hand, the light source is quite close to the object. My gut tells me that the sphere side facing the light, has to have values brighter than 128,128,128 (Original material values). I assume that the correct value is somewhere between the result shown in the pictures. What do you think?

[sirio76]

That problem is not about camera exposure, it’s about tone mapping. If you compress the highlights from the VFB you can get the same brightness and avoid the overexposed area.
For real world value of camera exposure I mean that if you use calibrated lights then you can use the same exposure values you would have used on a real camera with the same lighting condition.

[KushKush]

If you compress the highlights from the VFB you can get the same brightness and avoid the overexposed area. .

I assume you talking about the highlight slider inside vfb exposure. If I'm doing animation, do you suggest VFB corrections? Or make all of the changes inside comp software?

[sirio76]

Yes, to compress the highlights use an exposure layer.
VFB is extremely powerful in Vray5 so you can do most of your postproduction there, I use other tools (PS and Nuke) only for minor adjustments.

[KushKush]

Ok, thank you for the answers and tips.