How to get the depth from custom shader objects in fragement shader

Hey,

I tried all I know, and I think I only need a tag or something like that.

I want to write a DoF shader and for testing I show the depth as gray value.

This is the code in the shader:

float depth = Linear01Depth(tex2D(_CameraDepthTexture, input.projPos.xy/input.projPos.w).r);

and I also do this:

camera.depthTextureMode = DepthTextureMode.Depth;

I render the stuff as a post effect with this:

    void OnRenderImage(RenderTexture source, RenderTexture destination)
    {
        Graphics.Blit(source, destination, material);
    }

the material is created from shader.

If I change the RenderingPath to Deferred Lighting it works well, but if I use Forward, the screen is white. The shaders of the objects I render are custom, so if I change the shaders to standard ... e.g. Diffuse ... the forward-rendering will work.

I think I have to add something to my custom shaders ... but what?