Dumb Iray Questions: When lights get in the way or cast odd shadows

Serene Night

I have a question. How do I troubleshoot issues where a light blocks or creates problems in a render? These issues aren't usually apparent in the viewscreen but become visible after a render is in progress by rendering a big black bar across that section of the render. (see example)  I am using one of Elaineck's sets. 

When I stopped the render and switched off the point light in question, the blocked area goes away. 

I'm not sure what causes this to happen is there a way to troubleshoot this?

Please ignore the pokethrough on the outfit. It is a wip.

Tottallou

The black box is the Light Geometry & I have had this issue in images -  I usually just move the offending light away from the frame

I don't know if it can be made invisible when its a Daz Light , if it can I would love to know so will be watching for other replies :)

Tobor

If it's a black shape, and if it's a standard D|S light type (point, spot), it's the back of the emitter, and it can be made invisible by going to the light properties and turning Render Emitter to off.

(Note that this method will not work unless the view of the light is direct to the camera. The camera will pick up the emitter if the light is reflected, or shines through a volume, such as a fog effect or light shaft.)

If it's an emissive shader, you have to trick Iray by using a hack, such as turning the Cutout Opacity to 0.0001, or dialing out the refraction index (refection and weight set to 1.0). Both are imperfect, and alter the character of the light in certain ways, but they work to hide the emission surface.

 

Cris Palomino

With mesh lights, you can try a cutout opacity of 0.00001 (Might have been five zeroes).  DimensionTheory pointed this out and it works well.

Tottallou

The lights the OP means are Daz Lights not Mesh lights as I have these sets - 

I tried Tobors suggestion of Render Emitter off but on the render I was testing that left a big square shadow although it got rid of the black box so I stuck with moving the light out of the camera view :)

 

 

 

Serene Night

So far pulling the light back is the only thing that has helped. However these pre made lights are designed to point at things set at zero and close to zero. It is seems strange to have the light visually depicted in a scene. Any further suggestions would be helpful.

Khory

I'd say it seems more realistic to have lights visually depicted. Photographers and lighting people deal with that every day in real life. When it happens to me I simply pull the light/s back until they are outside the frame then check to make sure that the light levels are still what I am looking for.

Tobor

There are some light sets that are made to look like studio lights, and so they're designed to be shown in the scene -- depicting a photoshoot or something. I don't know the light set you're referring to. 

There isn't a way to prevent the geometry of the built-in D|S lights from casting shadows. The only things you can do is reduce the emitter size (which increases the sharpness of the shadow), or move it, or change to a mesh light, and alter the opacity. Obviously, each one of these has its varied effects. Simply moving the light, then adjusting its cone, falloff, and luminosity, is probably the least distruptive.

fastbike1

You can also change the camera position, focal length, or focus distance. No different than for an actual photograph.

Serene Night said:

So far pulling the light back is the only thing that has helped. However these pre made lights are designed to point at things set at zero and close to zero. It is seems strange to have the light visually depicted in a scene. Any further suggestions would be helpful.

 

evilded777

I have had some odd instances where the geometry of one light caused a shadow or abberration on the light cast by a different light. Its quite frustrating, especially when rendering to canvases and you think you can assume that the light is "not even there" for the purposes of a canvas, but its geometry still somehow interacts with the active light source. Weird.

Serene Night

Thanks evilded777 that is so true. I hate that when it happens with a canvas especially since I set them up to render and frequently leave to do something else.

 This seems like a glitch to me because none of my lights are in the scene. I'm not sure why they would be visible. 

 

nonesuch00

You can use Sun & Sky to light the scene. From the shadows it looks to be about 18:00 in your scene.

Serene Night

Thanks nonesuch. I tend not to use the sun and sky settings. I'm an old 3delught lighter and am more familiar with positioning my own lights. I do want to get to the bottom of the weird shadow issue because it is frustrating to have your image blocked out by black boxes.

 

I did resolve the issue by pulling the light back. But I want to do more to prevent it from  happening if I can.

nonesuch00

Serene Night said:

Thanks nonesuch. I tend not to use the sun and sky settings. I'm an old 3delught lighter and am more familiar with positioning my own lights. I do want to get to the bottom of the weird shadow issue because it is frustrating to have your image blocked out by black boxes.

 

I did resolve the issue by pulling the light back. But I want to do more to prevent it from  happening if I can.

You can move the camera in between the lights & the focal subject & reduce zoom if there enough room, but that might cause the camera itself to have a shadow casted though...do DAZ cameras have volume? 

Serene Night

I haven't used volume too much in Iray, since it does stagger rendering time a lot. I've used it in 3delight and it works fine.