fix shader for orthographic camera

I found an iris effect shader that works great with a perspective camera but is invisible with an orthographic camera.

It looks like a simple shader but I can't figure out what I need to change to get it to work with an orthographic camera.

Here's the shader: http://wiki.unity3d.com/index.php?title=Procedural_Circle_Mask&oldid=18030

Any suggestions?

Thanks

 

fixed it with this

Cull Off
Lighting Off
ZWrite Off
ZTest [unity_GUIZTestMode]
blend SrcAlpha OneMinusSrcAlpha