alpha value dependent of normal

is it possible to have the alpha value of a material dependent of the normal, the way ramps do for color?
i want to make a material that turns invicible when the direction of the normal is perpendicular to the camera. does anyona have a good idee?

That’s called the Fresnel effect.

In the Mirror Transp panel, turn up Fresnel. I think you need to be using RayTransp for it to work.

Fresnel isn’t normal to the camera. You could try parenting a lamp to the camera and play with fresnel and specularity but this may not be what you want. It would be nice if ramps could be added anywhere in the texture stack but they can’t for now. I don’t know of a plugin or work around for this but others may know better.


Ah yes, I misread - the Fresnel effect makes things transparant when the normal faces the camera, not when it’s perpendicular. For this I’d use the oldskool pre-ramps style:

Create “Blend” texture, set it to Sphere.
In map input choose “Nor”, and set the axis mapping buttons to blank, blank, Z. In Map To, turn off Col and turn on Negative Alpha (click Alpha twice). Set the material’s alpha to 0.

This incidentally was how Fresnel used to be faked most of the time before it was added as a feature, just with a positive alpha for the texture instead of a negative one.