Here is what happens when I plug the memory with photos (RAW) to a card reader connected to my PC.
- The PC will ask if you want to launch the Lightroom (LR) importer (I think it could be the same in Mac environment).
- Once the LR started, it will read the memory card
- If there are 40 images in the card and 10 of them are old and had been imported to LR already, the LR will skip those and list the rest of the 30 images and check them for import
- You can uncheck the one you do not want (i.e. heavily out of focus photo) and then hit the import button.
- LR will import the photos to the computer (your predefine location) and then unmount the flash memory card for you so that you can just remove it from the card read right away.
- Now the new photos are in your computer and ready for tagging, POST and whatever functions available in LR.