You don't import the photos into LR on the Mac, you open the catalog file (which you also need to transfer from PC to Mac), and then you reconnect the photos in Lightroom via Adobe Lightroom - Find moved or missing files and folders
DJ is absolutely correct. However, what format is your external drive? If it's a Windows format it may be "read only" on the Mac.
I'm new here and cannot see if my reply went through. I never had LR on the Windows desktop. I put the images from the desktop onto the external and then tried using LR on the Mac. Is the problem that I am using the same external hard drive to get the photos from Windows and then put them into LR using MAC? does the external h.d. get formatted for one vs. the other? If so, is there a way to format an external hd for both? I was hoping to use the Mac for photography.
External drives get formatted for Mac or Windows but there is some compatibility between the two.
If you plug the drive into the Mac, click on it one time to select it in the Finder, and then Get Info about the drive the Info screen will tell you the format.
Get Info by going to the File Menu and picking Info or by pressing the Command Key (it's next to the spacebar) and the I key while the drive is selected.
In the General section you'll see Format.
The Mac can read NTFS (the default Windows format) but not write to it.
A better choice for using a drive on both platforms is FAT32 although there are issues there, too.
Thank you for your help thus far. When I bought this external drive, I was told it was compatible with both windows and mac, no problem. I checked as you said, and it does say it is formatted for Windows and read only. Is there a way to reformat the drive without losing the pictures? I have every one of my images on here, some of which are extremely important to me.
You cannot format the drive and keep what's on it. Formatting completely removes the contents of the drive.
Are the pictures still on the Windows computer? If they are, you can reformat the drive and then copy them again.
Or, you can copy the pictures to your Mac drive and then format the drive for the Mac and copy them back to the external drive. This is probably a better option. If you intend to use the drive with only a Mac computer, formatting it with a Mac format is a better idea.
Only format with FAT32 if you want to be able to use the drive with both Mac and Windows.
I deeply appreciate your help with this. (I also deeply miss the days of the darkroom, where I knew what I was doing). If I might bother you one more time -
All photos are on the external hard drives. (both done the same way and read only on the Mac) If I am following you - I plugged the external into the Mac and moved a folder of images onto the desktop. It looks like it went from read only to not locked. Is this possible? So it seems then that if I buy another external hd, and use it on the Mac only so it is formatted to the Mac, I can then move the folder from the desktop of the Mac onto the external hard drive and then use it in LR. Or am I missing something? Of course having every photo for the past 11 years..this could take awhile. But is this the idea?
Again, thank you for hanging in there with me.
"I plugged the external into the Mac and moved a folder of images onto the desktop. It looks like it went from read only to not locked. Is this possible?"
Yes, that's exactly what happened. If you buy another drive, you could copy from your existing drive to the new and your files will be read/write. The new drive will have to be formatted as an HFS drive (that's the Mac's format). If you need to format it, you use Disk Utility which is in the Utilities folder on your Mac. Be careful with that -- it wipes out whatever is currently on the drive. Make sure you format the right drive.
I keep all my images on an external drive, too. In fact, I have two matching drives and sync them so I always have a backup.