I posted this a while back and got exactly zero response. So I’ll try again…
I’m trying to do some astronomy-related work involving semi-transparent sheets (representing a nebula of some sort) and using the stars in the world settings.
I can use z-transparency and see the stars through the sheet. However, if I use ray transparency, I don’t see any stars through the sheet.
Is this a bug or a feature? What is the trade-off by using z-transparency vs. ray?
I did not check the .blend but one way to overcome possible limitations of the star system is to render it in layers and combine afterwards in the compositor. Basically you need to create a render layer containing only stars (this is probably best done as a separate scene as stars are a world property) and a render layer containing your nebula. After you have set up render layers, you can use for instance Alpha Over node to combine them in the node compositor.
Check documentation and release notes for more information about this approach. If you get into trouble, I can make you a simple example .blend showing how to do it.
I do want to learn compositing, so this is a good place to start I suppose. This will kill two birds with one stone…
I’ve also had an issue with small stars flickering if the camera is moving. I’d thought of blurring the starry background and adding it to the foreground scene using nodes.
Thanks for the advice and I’ll take you up on the sample blend file if I get stuck.