Hello Stwert!

Thank you so much for your reply, I have tested your technique and managed to get things working! Really appreciate your help. I have one follow up question, and thought it would be worth asking, I hope thats okay. I have attached some pics to help explain my issue - this is just a test scene I have set up). In the scene is Maya's physical sun and sky lighting and rendering using mental ray. As you can see when the object is fully transparent there is still some shadows occurring. As the object grows the shadows grow darker (which is good) but I don't really want this ghostly shadow that is also there - it gives the game away that there is an object there which is just transparent at the start.

Any help or advice would be great, thank you!