Using VrayLightMeter to Estimate the Exposure

day
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.

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VRay Physical Camera Exposure (initial point to work) using VRay
Lightmeter

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
situations.
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:

Vray Physical Camera Tutorial

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:
Ev=Log N2/t
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:

Equivalent Exposure Value Chart

Exposure Triangle cheat sheet

Lux to Exposure Value (EV) and EV to Lux Converter

Watts / Energy Used vs. Lumens

night

21 thoughts on “Using VrayLightMeter to Estimate the Exposure

  1. Marcello Campagnoli

    Thanks for sharing my friend, very helpful as always excellent contributions!!!!

  2. That was interesting. I didn’t even know there was such a thing as a Lightmeter.

    Thanks,

    Peter

  3. Marium Siddiqui

    I cannot imagine how to thank you.
    You are Awesome!

  4. PERFEITO, MUITO BOM !

  5. Thanks bro ! you ‘re the best

  6. Thank you so much for your lessons!

  7. Great as usual

  8. outstanding

  9. This is really useful. especially for lighting designers. I had previously worked for a company as lighting designer. but I was using more of Auto CAD and Photoshop. but I was not sure how to calculate lux level of light in 3ds max vray. now you helped me. this is really wonderful work Austris.

    Many Thanks.

  10. wow so cool like it this tutorial Thank,s Austris.

  11. Спасибо огромное, очень интересно!!!

  12. thanks perfection

  13. огромное Спасибо, очень интересно

  14. great thanks!

  15. Orlando Hoyos

    Sinergia a montón, muchas gracias por compartir!

  16. Great tutorial like it this tutorial Thank,s Guru :)

  17. James Macdonald

    Very good, thank you. Muchas gracias Pablo siempre bueno aprender cosas asi para tener aun mas control, y lo explicaste de un modo facil de seguir, Gracias

  18. Thanks a lot! Great tutorial!

  19. Hello I saw Your lesson helped me a lot in setting up scenes, however, there’s one question I have after calculation of the set values are very low numbers, the minimum value almost equal to “0” and a maximum of up to 3000 (use the light from HDRI and plane v-ray)

  20. Pablo Conca Bosch

    BoNgO- I think may be you have low values in your scene… Because the HDRI do not have an a real scale value and may be you have the plane low too, the VRayLightmeter only measure the luxes on the scene, how you can see in my tutorial… but without see the scene I only can think that this could be the reason of this low values… Try to put you light sources with real values 10000–25000 lux Full daylight (not direct sun), 32000–100000 lux Direct sunlight… Or use a vray sun… :)

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