It's wonderful, Paul! I hope to be able to try some sky alpha planes sometime soon, too. Yves, it is basically just an image object. The "alpha plane" object is new for v.4 and all it does is automate portions of the process. But definitely you can follow the process in v.2. Create a plane object, then open the Material Editor. On the color tab, select mapped image, then navigate to the prepared image you want to use. Move to the Transparency tab, set the slider to 100% transparency and mark the box for "variable". Then to the right, the variable function will appear. Right-click the function and select "Edit Function". In the new function panel select "mapped values" and the picture option will appear. Click the Picture button and navigate to where you stored the prepared alpha image. The plane object will need to be set up to face the camera, and may need to be rotated if the image appears backwards. Also, in v.2, beware the Blue Gunk -- if you have too many transparencies in a scene, the portions that are meant to be transparent will begin to appear blue rather than clear. There are some tips for working around this in the Archive Tips collection in our forum Annex area. Have fun! :)