Camera Exposure vs. Light Adjustments

[3ddesign]

I've inherited a model that is over lit and am wondering if upping the vray camera f-number is appropriate rather than adjusting the 20 or so lights. Also, a brief explanation about what is happening internally when the camera exposure settings are adjusted would be very welcome (curious minds want to know).

Thx. Craig

[Neilg]

I've inherited a model that is over lit and am wondering if upping the vray camera f-number is appropriate rather than adjusting the 20 or so lights.

very much so, yes.

[Alan Iglesias]

...Also, a brief explanation about what is happening internally when the camera exposure settings are adjusted would be very welcome (curious minds want to know).

The F-Number in the Vray camera refers to the same thing on a real camera lens, or simply put, how big the lens apeture is. Since the number is actually a ratio (n:1) the larger the f-number, the smaller the aperture is and the less light is let in to the camera's focal plane. Unless you are working to create bokeh style-shallow DOF blurry effects (and have that turned on of course), then changing the number will effect your over all exposure only.

You may also use the camera's shutter speed to change the exposure as well. By the same token, if you have moving parts in your scene and the camera is set up correctly, you can get motion blur effects along with exposure changes.

You can also use the camera's ISO number to change the overall exposure. As it is meant to be the same thing as the camera's (and/or film's) ISO setting, it will change your exposure but as the Vray render is not affected by film grain or a less-sensitive digital sensor, there will be no image differences as you change the setting except in exposure.

-Alan

[glorybound]

I think, if your a purist, you'll want to fix your lights. There is a VRay light listener.

[peterguthrie]

If all the lights are balanced relative to each other, I can't think of any reason not to adjust the camera. That's what we'd do in real life isn't it?

[3ddesign]

Thanks for your responses. Upon further digging into the model I discovered that the VrayCamera Exposure box was unchecked. I asked the architects if they did this on purpose and they said yes, they always set up their scenes this way. Does anyone else out there use the VrayCamera without using exposure?

Craig

[Alan Iglesias]

...I asked the architects if they did this on purpose and they said yes, they always set up their scenes this way. Does anyone else out there use the VrayCamera without using exposure?

Craig

He he...yeah, I learned some time ago to always work with an imported camera created in a new file when working with other people's files. There are so many things that people can change in the camera settings that you could chase things for hours. I guess it is just easier for many poeple to use a simple camera with no exposure, but that defeats the whole purpose of using a physically based renderer.

When I am instructing for corporate Vray training, I always include photographic theory and how it relates to using Vray. This case, the ability to easily change the exposure without messing with a bunch of lights (and keeping the lights' relative brightness intact!), is only one of the many advantages the Vray physical camera affords.

-Alan

[Neilg]

that defeats the whole purpose of using a physically based renderer.

How is this even remotely true? All it does is add terms that you're used to seeing on real cameras to control stuff you could already control just fine before. The physical camera doesnt change the way vray works.

[Alan Iglesias]

...The physical camera doesnt change the way vray works.

I never said it changes the way Vray works, and I apologize if you got that impression. But I am saying that it does make the way it works even better, more realistic, and have much more versitility! ...my opinion of course.

Basing the renderer and camera on physically real-life stiuations gives everyone a reference point from which to start, if you wish to use it. You can use it this way or with "smoke and mirrors" so-to-speak, or a combination of both, which I often do because not all scenes I create are based on real-world situations. This is the power of Vray that I love so much!

...All it does is add terms that you're used to seeing on real cameras to control stuff you could already control just fine before.

You could control it true, but not "just fine" as this example clearly shows. It will most likely be much easier and faster (as Peter points out) to change the camera exposure than change all the lights to fix the overlit scene. If not, there are other ways to get there!

And I truly hope that it is not all it does (Have some fun with the Vray camera's bokeh effects!). If that was true then all the development hours put into the Vray camera would have been a waste, and I would imagine that the Chaos Group has a much better handle on their time management than that!

But ultimately you of course should use Vray the way you want to. It's really none of my business and I would never try to change the way folks do things unless I was hired to do so (which I am quite often). I'm only replying to your post to clarify my points to the rest of the forum.

All viewpoints are valid and I thank you for your comments,

-Alan

[Neilg]

It will most likely be much easier and faster (as Peter points out) to change the camera exposure than change all the lights to fix the overlit scene.

I wasnt talking about that. Multipliers in the colour mapping - move the bright & dark together.
I'm using it the way I want, and you're free to aswell, I just wanted to point what you said about 'defeating the purpose' was nonsense.

(The bokeh effects are also in the vray settings for standard cameras. Using a standard camera also means you can have a viewport preview of DOF & motion blur too, which the vray camera cant do)

[Alan Iglesias]

Well, it absolutely defeats the purpose of having the physical camera if you do not use it, which is what I meant and probably should have said in the first place.

I guess that for me and many (really all) of the folks I know that use Vray, the camera and renderer work hand in hand and for us that is a thing that seems to be such a great feature. Not everyone thinks so, and that is of course the way it is and that is that.

Your points are well taken!

-Alan

[glorybound]

I have noticed that when I use real world settings, things look the best, and it is predictable. I usually pull out my cheat sheet, set my camera to a real worls value, and increase or decrease my lights (hdri).

[peterguthrie]

I have noticed that when I use real world settings, things look the best, and it is predictable. I usually pull out my cheat sheet, set my camera to a real worls value, and increase or decrease my lights (hdri).

Sounds like a reasonable starting point, but from there the great thing about the vrayphysicalcamera is being able to finely adjust the exposure per view. You wouldnt just keep the same settings in your dSLR if you were say, shooting into the sun or away from the sun.

Once I have a scene set up with the lighting the way I want it, none of the 20 or so cameras have the same exposure values, each one is set up individually (like it would be in a real world situation.)

[andybot_cg]

Also, in favor of proper camera exposure: wouldn't you run into inadequate sampling with incorrect exposure (i.e. scene is underexposed, the dark areas will end up splotchy; overexposed will be blown-out)

[samuel_bubat]

I guess it is just easier for many poeple to use a simple camera with no exposure, but that defeats the whole purpose of using a physically based renderer.

Wrong, your rendering is physically incorrect this or that way because you don´t have physically correct materials. A very important point that is
neglected by basically everybody. A trick question.. at wich lighting condition and wich camera settings do you have to photograph a texture so
it´s physically correct ? Well.. you can´t.. or in other words it´s trivial . You´d probably have to BRDF measure each and every material in your scene
if you really want everything "physically correct".

Also a physical correct rendering simply doesn´t exist.
All you can get is a physically correct light distribution. A photo can never really reflect what your eye can see. A photo is extremely limited
because.. well that´s how the real world works
And also what your eye can see depends on a lot of factors. For example if you stare at a red area for quite some time
the "white balance" of your eye is completly different to someone who didn´t do it.
So below the line it doesn´t matter if you adjust your lights, your camera or your materials as long as the result is what you had in mind.