help rendering for still composite
 

ok so i have a scene with a car model, a curved plane for the floor/backwall, and a sphere with a HDR image on it for lighting and such, i'm trying to render it so that the floor/backwall and the sphere aren't there so i can composite it over a preexisting image in PS. i need the lighting and reflection info from the sphere but not it visibility it the background, and i need the shadows on the floor but again not it's visability anywhere, i'm running maya 2008, any help would be awsome thanks in advance

have you tried a 'use background' shader on the floor?

What Neo said..

Or use render layers and composite each layer into photoshop for adjustment

Select the objects you do NOT want to see in your final render, and in the attribute editor for each object, turn off "Primary Visibility".

The objects will still contribute to the scene, cast shadows, color, etc, but they will not render in the render view or the batch renderer.

ok thanks for the responses, i turned off the primary vis and rendered and got the car with the alpha everywhere else now i just need the shawow pass, how would i go about doing that, i'm assuming layers but i have never used the render layers how would i set up to just render the shadows?

use background :)

if you apply that shader to the floor it won't be rendered, but it'll still receive the shadow from the car or surroundings and it will also create the alpha for that shadow for compositing later on.

does the use background shader not work without lights, cus when i render with MR & FG it doesn't seem to be working, it's still there visibly and no alpha mask

ya know, i'm not sure... i've never used 'use background' for non maya software renders.