Dielectric Material and Transparent Shadows?
 

hi @ all. first: i am new to this forum and i would like to say hello to everybody in here ;) i'm a german so please be aware of my english capabilities :))

ok so now my problem: i use maya and i would like to use mental-ray for creating a nice piece of glass. so i assign a standard blinn or phong material to the glass, go to it's shading group and assign a custom shader to the material slot ... of course: a dielectric material ;) this gives me the look i want to achieve - but probably not the shadows i expect from a real glass surface :( after assigning the dielectric material in the shading-group, my transparent shadows are gone although i have activated the raytrace-shadow and generously raised up the trace-values.

i have studied several workarounds for that (for example assigning a custom shadow shader (the transparent one) and connecting the IOR of the dielectric to it's transparency) but everything dont work. my question now is: how can i get beautiful transparent shadows which are based on the IOR of the dielectric material (which normally is the natural behavior) ??? it would be great, if someone has a solution for me !!!

many thanks !!!!
s2k

well ... here are some images for comparison. a torus, with a dielectric material assigned to it and a spot-light which casts the light. and for comparison the same scene again rendered with brazil ... and there you can see those transparent shadows which i would like to achieve with mental-ray too:

mr dielectric-material: http://www.subbz2k.com/misc/torus_mr.jpg
brazil glass-material: http://www.subbz2k.com/misc/torus_brazil.jpg

these 2 images are all rendered in the same conditions within 3ds max. i reduced the overall quality to improve the render speed but the differences should be seen. with the brazil rendering you can see those transparent shadows which are generated by a simulated area-light. notice that they are generated within the surface too (what a beatiful natural behavior :) ). in the mental-ray rendering you see a sharp edged raytrace shadow (because within 3ds max i have to change the light-source to generate area-lights with mental-ray but this is incompatible with brazil so i left off) but the important thing is the absolutely black shadow: that's not correct.

so again: can somebody tell me, how to get those transparent shadows with the dielectric material as shown in the rendering from brazil ??

plz help i'm out of ideas :(