Use the menu command Library->Previews->Build Smart Previews
Thank You for Your response !
..I understand that i can do that (rebuild previews as soon as I connect the HD with the original files),
do You mean that having previews -and smart previews- to follow collections-exported-as-catalogs is not even possible in the first place?
I don't mean that. I don't know, I have never tried to do this. For what its worth, I use a single catalog for ALL my photos, and so this problem would never arise for me.
Smart Preview are part of the Catalog. They do not export when exporting as a Catalog. In the new catalog you will need to build smart previews again.
First part of Your answer does not contribute to better understanding in conjunction to the second phrase. However the message is now understood. Maybe this first part could read :
1)Smart (any?) previews never leave a catalog.
2)They do not export when exporting as a Catalog. In the new catalog you will need to build smart previews again.
Seems exceedingly dry to me that LR does not state this (remind of) in the info-statement windows.
Thank You for having followed this up and settled the doubts.
When you export as catalog, you should be checking the box that says Build/Include Smart Previews. Are you doing that?
Oh no..I did not see that, and Indeed I overlooked it; the possibility (necessity) is there to tick so right at the start !
Thank You so much (meanwhile I went to the trouble to get the external HD I had not with me at the time) to "repair" the situation by rebuilding smart previews.
Now I will know for next time !
( ..And so You started to think about that exporting a collection to become an independent catalog -temporarily or not- could come in useful for You to ?!)
Thank You !!
Meanwhile new contribution brought the correct answer :
Exporting (smart) previews .. is available as on option, not automatic, when exporting a collection as a catalog.