I am rendering a spot light through a fog object. The spotlight has a fairly high angular falloff to give a soft edge. However, within the fog object, the light has a hard edge.

In the image below, I have rendered two identical spotlights, one of which goes through a fog object. You can see the difference.

Is this intended behaviour or a bug?

Thanks
Richard

Are you using the volumetric light option?

My guess would be that the fog mitigates the subtlety of the falloff. Have you tried using the light cone instead like ren_mem said?

Which volumetric light option? Do you mean "Enable 3D shadows" in the Light Cone section?

The above images were rendered using the light cone with 3D shadows enabled (if that's the same thing as volumetric shadows?) and a fairly high "shadow buffer" setting in case the volumetric fog required extra quality to retain the soft edges.

Thanks,
R

I meant light cone options. It's kind of a loaded question. Don't know specific options in scene or render. Really hard to say if it is a *bug*.  There are several options w/ soft shadows, lighting, light cone and render options that come together. Are you saying you did 2 identical renders in carrara and you feel one is allowing the light to pass thru the fog and one isn't? I didn't do raytrace or GI just light thru trans and got a pretty soft look. As to whether it is an exact physical simulation...well another loaded question.

In the image I posted above, the right hand spotlight (with angular falloff) is shining through fog, and this produces a hard edged light.

The same spotlightcube was copied and pasted to the left hand side of the image, but with no fog, and the light cone creates a soft edge as it should.

I would have thought that the combination of fog, soft edged shadows, angular falloff etc would add to the softness of the outline and not make it harder.

Well, the one above is high falloff over a fog cube, there is also this setting (falloff) in the light cone area. Higher render setting and enabling soft shadows w/ light thru trans in both places if using GI also matter. You have to play with the settings. Not sure what might be wrong. If you think it is a bug report it.

Stranger and stranger ... have noticed that this hard edge effect does not happen with volumetric clouds in a similar setup!

Picture to follow - my web hosting is down.

 

Did you try altering fog density, the shape or the width? Not really all that strange. It could be the way the light edge is hitting the fog box shape.