Art,
Is there a reason you're sticking to the 4990 since it sounds like it's not working to your liking? Why not use your v500? Do you also have large format (the only drawback I can see of the v500, which does not do large format)
I shall give that a go. I get better results scanning of the bed that using the slide holders. Which is shocking ,the transparencies are perfectly exposed and sharp, but the scans always come out very poor.
Thank you.