What difference? I can’t understand the difference.
They relatively do the same, but I think there are some instances where Ray Transp cant be used or some such thing, anyway so far I’ve found RayTransp to look more realistic, but thats my personal opinion.
When you apply Alpha to a material, it just takes the background to show through. Pressing Ztransp makes Blender render it correctly, in that things behind it will show through. Ray Transp, on the other hand, uses raytracing to actually simulate the refraction (used for glass and such). With Ray Transp you can choose an IOR (how much light is bent). When you just give the Ray Transp an IOR of 1.000, then the results are the same as Ztransp.
Ray Transp also does not work with halos and stars, a really annoying limitation if you’re trying to work with say, a spacefighter cockpit with distoration around the edges of the glass.
Here’s a crappy example pic that I couldn’t get good lighting on.
Ray transparency can also do burry transparency if you use the latest builds.
Star Weaver, use camera aligned planes with a halo blend texture, they work with ray transparency.