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Let's say I have a cut glass chimney over a light and it's set quite close to a wall. I would love to get the light patterns from the cut glass onto the wall. I've been experimenting with a simple faceted goblet I made, but have had no luck. The glass material I'm using is just your generic high grade glass with attenuation set at 30 meters. The wall is right behind the glass. I've tried a sphere with emitter inside the glass, a copy of the glass hidden to camera (REALLY no good), and a plane with emitter shooting through the glass. I've varied the hidden settings on these lights, moved them around. I'm a bit of a beginner so I don't know how to analyze this.

kk

Was the plane that you used quite small? For sharp caustics you need a relative small plane emitter, say 0,5 x 0,5 cm.

Ah, yes. So a smaller emitter gives a sharper light? I'd been wondering about that since what I need for this effect is a really sharp light source.

I will try.

Big and far, or tiny and close in fact

So that is how you control the lights? I like the quality very much except I would really like to get some good old hard shadows sometimes. Big and far would be like the sun, right? I haven't gotten small and close to work yet, though. I would really like a nice hard spot to work with. Then how about a a beam going through a mist? I'm quite interested in these effects.

kk

Yeah, the way lighting in everything works is that a small light (like an icandesant bulb) source will give sharp caustics and shadows. A larger, more diffuse source will give softer caustics and shadows.

For an example, if you use a point and shoot camera with a flash and are photographing a face, you might see a hard shadow of the person's nose on their cheek. If you use a larger light, like a softbox, you won't see a shadow of that person's nose. Lookin at a model in a magazine ad, you'll notice there are no hard highlights or hard shadows because they are using a softbox or something similar.

I think there are videos in either the tutorial or resources section that a user made that gives really really good explanations and examples of lighting properties exactly like what you are asking about. When I get home I'll look up the link for you.

Thanks. I would appreciate that.

kk

Another thing to think about is the distance between the object and its shadow, near is hard, far is soft, but added to the size and distance of the light source as said previously.
Could explain this way better if it was in my own langage, sorry

regarding the overall light properties, here is a link to the video tutorials
http://www.youtube.com/watch?v=4CKGfldpBtw

if you look through some of the other videos on that page, they are very helpful as well. These same properties, and what def4d mentioned, apply the same to caustics the same as it does shadows.

Seeing the video really helped get it set in my mind visually. I'm from film. You want a soft light then you use a KINO. Hard light has some kind of lens and is usually big. The light spreads from the emitters differently than I imagined. I was surprised to see that tiny emitter lighting the whole model.
I don't seem to be able to attach files here so I've put up 2 of the images on my site. The one with the cut glass still doesn't give me the cut glass patterns I wanted. Both need some work, but I got this far with your help. Thanks.http://www.kkingart.com

Next up is the light through the mist.