I´m modelling a Saturn-like planet, and for its rings I simply used a plane with a texture for the rings. It´s a simple PNG file (no alpha), so I used for the material a white color, the image texture as an ALPHA, alpha value as 0 and Ztransp activated. I rendered it, but unfortunatelly, the light over the rings plane also affects areas of the plane that should be transparent too (please see the attachment). Any tips?
Thanks in advance.
oh i had the same problem…i believe i found a solution but i cant remember at the moment. ill try to recall it.
No knows it? 
I’m pretty sure it would work if you actually use alpha in the png or you could also try a specular map to make the specular highlights only on the rings.
you could make a ring easily and texture that…or you could make the rings not have specularity.
Leandro: u still around? 
i found it! http://wiki.blender.org/index.php/Doc:Tutorials/Textures/Use_Alpha_for_Object_Transparency
good luck!
You need to depress the specular button as well as the alpha button in the ‘Map to’ section of the material.
I also find that you should apply the same texture twice, the second one in ‘multiply’ mode, and only affecting the specular and alpha. This makes the transparent parts way more transparent.
Matt
Thanks and sorry for the delay. I´ll check it out. 
