Digital Art Zone

Really nice pictures over there. I left a few comments…

Just to clean up my previous blunder, here is the setup and result for a correct light rig.

The lights producing the mirrored beams have to be on mirrored positions (of course…). I abandoned the 3D Shadows Invert setting and went for excluding the mirrors from the lighting instead. The mirror in front of a reflected beam light is on the “All objects except:” list of this light. So the light as well as the light cone go through the mirror and show properly between both mirrors.

With the mirror reflection set to 90%, each reflected beam is set to 10% less than the previous one (light cone intensity and light brighness).

The “Fog/Use gel” setting in the Light Cone dialog also reacts to the Angular Falloff setting of the lights, which adds to the credibility of the fake beams.

Masking out the surplus beams turned out to be much easier than I had expected. I rendered the complete scene, then only the stage, and at last only the two mirrors with the Scene Background color set to white, and with Multi-Pass element Background switched on. The latter provided the contours of the mask to cut out the complete scene. Pasted that onto the empty stage, and got the cleaned-up result.

Pictures below:
- Light positions and beams
- Complete render and stage render
- Background pass and mask
- Final composite

This setup also works with objects intersecting the light beams.

To shape the reflected beams like the original one, the objects in front of the mirrors have to be duplicated in mirrored positions just like the lights.

The mask for this picture was the same as above.

Pictures:
- Lights, mirrors, and objects from above
- Complete render
- Final composite

I wonder, for creating the masks, have you tried to see if the light cone respects the shadow catcher?

Just wondering whether anyone has tested this concept in real life?  After reading this, I was tempted, so went into my darkened bathroom with a flashlight and shined it on the full-length mirror.

What I got was the whole mirror lit up and made a reflection of the full mirror on the opposite wall, with a big highlight in the center of the reflection, as well as lighting up the whole room - no light cone at all.

Of course, my bathroom is not the size of Carnegie hall - it may behave differently in the great outdoors?

Roygee - 07 September 2012 10:52 PM

Just wondering whether anyone has tested this concept in real life?  After reading this, I was tempted, so went into my darkened bathroom with a flashlight and shined it on the full-length mirror.

What I got was the whole mirror lit up and made a reflection of the full mirror on the opposite wall, with a big highlight in the center of the reflection, as well as lighting up the whole room - no light cone at all.

Of course, my bathroom is not the size of Carnegie hall - it may behave differently in the great outdoors?

velly intewesting
maybe your bathroom is too clean…
you probably won’t see a light cone unless thereis a lot of air borne particles - eg fog
the reason the whole mirror lit up would probably be the internal reflections from the front glass surface
the back surface of the mirror, being imperefect, would scatter the light in directions not exactly 90 degrres to the incoming light and contribute to the internal reflections, plus dispersion, diffraction caused by a not perfectly clean surface etc…

Excellent points Roygee and head wax! Something I hadn’t considered. Another thing that I thought of when reading your posts is reflector telescopes. The mirrors for those aren’t flat. They’re curved like a parabolic dish and designed to focus the light into a tight point. Time for ‘nother experiment!

evilproducer - 07 September 2012 02:38 PM

I wonder, for creating the masks, have you tried to see if the light cone respects the shadow catcher?

There is indeed an overhead distant light in the scene. It threw shadows until I changed the Scene Atmosphere to Distant Fog, just to give the impression that there is something around that Roygee is missing in his bathroom :).

...

After reading your comment, Roygee, I went into the bathroom myself, curious, but it’s still a sunny afternoon here, so I couldn’t even see the flashlight reflected… But I think that head wax is only too right. At least the scene would still be correct, if still implausible, because the mirrors in there are optically perfect surface mirrors, like in a single lens reflex camera.

...

To get the shadows back into the scene, and still have some fog, I changed the Atmosphere this time to Sky, with just Mist activated. With the flashlight tinted slightly yellow, and the mist set to a blueish dark grey, I hope the impression of a spooky patio in the middle of nowhere is improving. At least I hope that this is, what Grimreaper originally had in mind.

The light cones and the light itself seem to work properly with the shadows. For the complete render, the helper objects are excluded from the distant light to not throw shadows themselves. For the stage render, the mirrors had to be visible to get the shadows on the floor. The mask is still the same as before.

...

Gentlemen, your ideas are horrible. I didn’t even dare to think about mirrors not beeing parallel. And even less about optically imperfect bathroom mirrors, or parabolic telescopes. But I would like to go on experimenting, too, and see how far Carrara could take us :)

Well, I didn’t set the scene up as nicely as GFHEL, but I did try a parabolic mirror and a volumetric cloud. I was still hoping the cloud would catch the bounced light from the mirror and the reason it wasn’t visible in my other renders was because of the light spreading.

For this render I turned on Indirect Light, enabled caustics and cranked up the caustics settings to the max- except the photon count. I set the spot to 400% with no falloff, the cloud to 200% brightness and 4% opacity and to participate in GI. Sadly, the light bounce isn’t reflected on the clouds although the caustics do show a tighter reflected light. I did turn ambient light all the way down and added a glow to the back of the parabolic mirror.

GFHEL - 23 August 2012 01:42 PM

You could fake the bouncing cone at least for one mirror.

- Set up a second spot behind the mirror.
- Set the Light Cone 3D Shadows to Enable and Invert. This lets the cone start behind the object.

Bouncing light just works by turning on caustics, regardless of the light cone.

Oh man….
Thanks for this! Now I can go in an fix every streetlamp scene I have… with pleasure! I’ve always ended up blocking the pointy end of the cone with the [supposed] light-source model, cleverly bringing the cone back behind it from the viewers perspective.

Yeah, I didn’t know it did that either! This is very helpful!

@Dartanbeck
@holly

Glad it helps. And I would be glad if I could start to contribute a bit to this forum after I have silently gained so much knowledge here throughout the past years. (At least every two months or so…)

Dartanbeck - 09 September 2012 10:26 AM

I’ve always ended up blocking the pointy end of the cone with the [supposed] light-source model, cleverly bringing the cone back behind it from the viewers perspective.

This is really clever. Sigh. That’s when I always wish I were an artist, not a technician, and knew about perspective….

evilproducer - 08 September 2012 01:27 PM

Sadly, the light bounce isn’t reflected on the clouds although the caustics do show a tighter reflected light.

I have been experimenting, too, without getting anywhere further than you. So I am faking again.

This is the radio telescope from the Carrara library misused as a projector. To get a nearly parallel beam, the second spot light is far back behind the reflector. The angle is set to 5°, lighting is restricted to the reflector alone, and the Light Cone is set to Invert. This neatly cuts out the reflector’s diameter from the actually larger beam of the second spot.

Hi Grimreaper

Because of the new forums , We’re all “members” or new members based on the number of posts.

you should be able to search,. but if you can’t,... Try logging out,... then log in again.  that should reset things.

Roygee - 07 September 2012 10:52 PM

What I got was the whole mirror lit up and made a reflection of the full mirror on the opposite wall, with a big highlight in the center of the reflection, ...

I played around with flashlights and found that they produce stray light around the center beam. It looks as if this could be the main source for the reflected picture of the mirror.

When I took pictures of the light beams to find out their angles, they also revealed that the two components had different focal points.

So in Carrara, I took two spots to mimic the two light components. A wide-angle spot near the front of the virtual flashlight, and a narrow one set back.

The wide-angle spot for the reflected light of the mirror uses a Gel Map to mask out the mirror. To get the map, I set a camera at the same position and direction as the spot.