It wont let me combine collections from different catalogs, or to export each of the 3 collections into one new catalog.
What would be the way to create a Slideshow presentation from three different catalogs/3 different collections.....There are over 40,000 u/w images, so there had to be multiple catalogs :-)
40,000 images can be in ONE catalog in Lightroom. There are people that have 100,000's of images in one catalog. The way to do this is to "Export as Catalog" three different temporary catalogs of the need files from each main catalog. Then "Import as Catalog" two of these 3 temporary catalogs into the remaining temporary catalog for your SlideShow. You have ran into the main reason to have ONE catalog.
I originally had one larger catalog, but it was running slowly....the voices of the community suggested this was too large to run swiftly, and that it should be split up......Maybe the issue is that it is on my Imac...instead of a PC...maxed out on ram, but still no where near as powerful as my PC. However, for photos the screen calibrated well to my epson 4880 printer, while the PC monitors that could do as well were at ridiculous price tags.
So....I will will try the IMPORT as catalog as you suggested...Thanks!