CGTalk - Light Divergence and Projection Size

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aaraaf

01-16-2006, 03:46 PM

Okay guys... here's my dillema:

Most light fixtures collect light through various ways and then project it. The bulb is the source of the light, but not necassarily the source of the projection. Think of a spotlight. The bulb isn't really that large, but a group of mirrors at the base help spread the beam to make it larger.

If I use a directional light I can control the size of the beam, which lets me control the projector size, but there is no divergence (how the light spans out as it goes). If I use a spot light I can get divergence, but can't control the size of the projector (which I think is 0 on the regular spot...)

I've been making both and using them together to get both divergence and projector size, but it sure would be nice to only need to control one light... which would help when you've got upwards of 10 light sources (20 individual lights this way!).

Here's my question:
Am I missing something obvious in the options that lets me have control both Divergence and Projector Size? Maybe it's time for a feature request...

I've been playing with lights for a long while, and have never really solved this to my happiness.

Rockin

01-16-2006, 04:29 PM

If you really need that control, you need to use area lights ;). They let you choose the size and shape of the emmiter, but the divergence options still remain.

charleyc

01-16-2006, 04:30 PM

This is essentially what the purpose of Area Lights are. You specify the size of the light emission. This comes with the most often desired benitif of nice soft area shadows, but it takes longer to render. Depending on your needs, this is a pretty easy thing to fake if the area light speed is a problem.

aaraaf

01-16-2006, 05:32 PM

Thanks for the info Rockin and charleyc!

I REALLY need to learn Mental Ray... getting it going is easy, making it sing takes a little more time than I've put in. I've got the area light on but can't get the shape to show up in a Volume Light render... it looks the same as a regular spot... I'm guessing it has to do with some of the mental ray Light Shader options.

charley c, I've faked it before, and it works well, but I've only gotten a look that I'm happy with using multiple lights, and I don't like having to control so many lights. I've typically used a spot coupled with a direction light, to get the base and the divergence. Have you had success with a different method?

Again, thanks!

CarlosA

01-17-2006, 08:18 AM

i belive max has a native area light now. so there might not be a need for Mental Ray.
cheers,
Los.

Rockin

01-17-2006, 09:22 AM

Unfortunately I don't think it's possible to make volume light work with area lights. They do work, it just seems that the volume light effect doesn't work correctly with them :(

If anyone knows how to achieve this, I would also be interested :).

CarlosA

01-17-2006, 09:46 AM

volumetric lights only work with mapp shadows in max.
whichmakes it a real bumber.
but the simplest work around to this is to do s separate volume pass. where you use a matte material or you add a black material to every thing with self illumination at full.
then you comp you matted volume lights with a screen or multiply mode.
the best thing about this aprouch is that it's quick to render and you can do some post to your volumes like brightness and contrast levels and stuff.
long live the comp!
cheers,
Los.

aaraaf

01-17-2006, 03:36 PM

Hey CarlosA I'll have to give your method a go. Just to finish the project I've reverted to a 2 light setup for each light... which I'll probably have to use for my next project as well because I don't want to comp it for other reasons.

I see you changed jobs... Every article I've read about the Disney CG stuff has had nothing but incredible things to say about the rigs! I wish I could have seen the display from Siggraph... every TD with a blog couldn't say enough...

charleyc

01-17-2006, 04:33 PM

If your main concern is to remove the effect of the Volume going to the point source, use Near Attenuation to clamp out the point. Offset this light as needed to align the clamp to your area light source.

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