This is a guest post by Pablo Conca Bosch from Spain
I think his technique is quite interesting, you can use the vray light meter as a real hand-held incident lightmeter. I must admit, I tried it some time ago, but upon finding out it gives lux values instead of something more usable, I quickly gave up and went back to guessing/using my eyes to determine exposure. After this tutorial, however, I can see that it is not that difficult to interpret the results and I already have a couple of ideas how to use this for fine tuning scenes.
VRay Physical Camera Exposure (initial point to work) using VRay
Due to other reasons…. (money mainly, lol) I don´t have manual camera and how it´s normal I
never use manual cameras, but I try to learn in depth all the theories that I can about
photography, to understand better how to use the VRay Physical Cameras (and a manual when
somebody leave me one).
And for this at first (years ago) I adjusted the VRay Physical Camera settings (F‐number, Shutter
Speed and ISO) with empirical method, one probe…another probe… and like this to find the
correct adjust… Work!.
Then I studied the exposure theory and the behavior of the manual cameras on photography,
and what are the most common settings for photography in different scene situations, and this
gave me an idea that how i could begin to look for a correct exposure on different scene
In this tutorial we have assumed that you have clear the exposure theory, if isn’t in this way
you can consult this great tutorial from Austris:
But at the end I had no a correct number based on the intensity of the light sources on the
scene, units that could be real or unitless…The units used on your light sources no matter
because due to the first measurement we do in this technique you adapt your camera settings
to the light you have at the scene, but I normally use real values for my light sources.
And a Saturday I went to the bed thinking about exposure theory and other stuff about real
cameras and too my last freelance work on mind (as always I had not satisfied), and on Sunday
morning when I woke up I thought… yes! I could do this to try to adjust…
The idea is find an initial point of exposure to begin the work in the scene with your VRay
Physical Camera using a Helper included on VRay Renderer (Vray Light Meter) and transform
the data given by this helper (iluminance/luxes/lumen x square meter) to F‐number and
Shutter Speed values, using this formula to obtain an Exposure Value (Ev):
lux=(2^Ev) x 2.5 x100 /ISO
Ev= Log (Lux/2.5)/Log (2)
An this other formula to obtain the final values:
Where N is the F‐Number and t is Shutter Speed
but… i think is better use the web… you will see on the tutorial.
In this tutorial you could see two cases, but it will be useful to find this initial point to work in
all the situations you could be immerse.
Here is the tutorial video:
The links shown in the video are: