Claudio, the reason that glass will be so much slower is because of the reflection/refraction taking place within the transparent surface. You'll find you have similar problems with scenes that have any reasonable amount of transparency involved.
In order to limit this, you can turn down the ray recursion limit in the raytrace options panel. By default this is set to 16 (ie: each ray cast from the camera will bounce up to 16 times). Setting this to a lower value will speed up your renders at the cost of some accuracy in reflections and refraction - try setting it to around 5 (unless you have loads of reflective surfaces in your scene) to get a reasonable speedup.
As for some accurate glass settings, try taking a look at Philips Jack Daniels tutorial over at www.liquid-arts.de (its in the techniques section). This should give you some settings to be starting with for very photoreal glass. |
