With VRay 1.5, there is a new parameter for a VRayHDRI. What is the the Render Muliplier and how does it work in conjunction with the Overall Multiplier?
The “Overall multiplier” is the old one that affects the HDRI as it appears in both the material editor and the rendering.
The “Render multiplier” only affects the rendering, so that you can still see and adjust the HDRI in the material editor.
Best regards,
Vlado
Thanks for that feature Vlado. Its a huge help. What is a good method for showing the HDRI in the viewport for positioning in a scene? Just putting it on a sphere?
Thanks for the new update!
or use the sky realtime updater from my scriptpack. it works with any background, and will allow you to freely rotate the hdri in the map and see changes reflected in the camera view 
When opening old scenes, this is a problem. For example in the old scene the hdri had a multiplier of 0.5. When you open it with vray 1.5, the overall multiplier is indeed 0.5, but the render multiplier is set to 1.0, resulting in brighter reflections in the rendering.
I don’t understand why both multipliers affect the rendering, shouldn’t one override the other then?
I thought this was strange too. The functionality seems to be, the overall multiplier is multiplied by the render multiplier…seems very counterintuitive.
Both multipliers are multiplied, so if you open the scene, all should be ok (0.5 overall * 1.0 render = 0.5, what it was before).
Best regards,
Vlado