Rendering in Arnold without Alpha

[Dantetron]

Hello, all.

I'm trying to render a simple scene using the Arnold renderer in 2018.  To keep it simple,  picture a scene with a sphere on a floor.  When rendered, I would like to have the 2 objects render normally in RGB (reflections, shadows, etc) but only have the sphere's alpha be rendered in the alpha channel. NO alpha for the floor.

This seems like it should be simple but I just can't figure it out.

Thanks!

[Dantetron · Accepted solution]

Okay, I figured it out myself and I'm a moron.

The solution is to apply the "Arnold Properties" modifier to the object you would like to manipulate. In this case I wanted the object to exist to the objects around it but create no alpha.

After applying the "Arnold Properties" modifier to the object, I checked "Visibility" and unchecked "Camera (Primary Rays)" under the General Properties tab.  But I kept all the other properties in this section checked.  Works great.