Somehow when I import photos from my camera, Lightroom duplicates all of them and creates a "...-2.jpg" file for every single photo.
Both sets of photos show up in the library and in "develop". I have to sort them out and delete all the "...-2.jpg" files.
How do I stop this function? Thank you.
What are your import settings.
Do a test import of some photos you shoot around the house and take a screen shot of the import window and post it here.
What OS are you using?
What exact version of LR are you running? Open LR go to the Help menu then System Info and post the exact LR version.
macOS High Sierra (10.13.2).
Lightroom version: CC 2015.8 [ 1099473 ]
License: Creative Cloud
Operating system: Mac OS 10
Version: 10.13 
Application architecture: x64
Logical processor count: 8
Processor speed: 3.5 GHz
Built-in memory: 32,768.0 MB
Real memory available to Lightroom: 32,768.0 MB
Real memory used by Lightroom: 2,568.0 MB (7.8%)
Virtual memory used by Lightroom: 8,249.0 MB
Memory cache size: 5,791.1 MB
Maximum thread count used by Camera Raw: 8
Camera Raw SIMD optimization: SSE2,AVX,AVX2
Displays: 1) 2560x1440
Graphics Processor Info:
NVIDIA GeForce GTX 780M OpenGL Engine
What camera are you using and how do you get the images from camera memory card to computer.
Card reader or connecting the camera directly to the computer.
Would you please take a screen shot of the import windows and post it to this thread.
Canon 5D mark IV and I import them directly by connecting the camera to the iMac.
Try taking the card out of the camera and use either the built in SD card reader or a dedicated card reader.
Also try Copying the imaged from the camera to a folder on your hard drive and then import into LR using the Add option at the top of the import dialog.
Thank you. I will try that in the new year, best.
When you connect the camera, do you leave cards in both slots (I assume the camera has dual slots, yes?) and if so how is the camera configured to use those slots? Do you use them the same way that I use my 5D3, i.e. new pictures are duplicated to both cards?
If the answer to both questions is "yes", then the likely explanation for the problem is that in the import dialog you have the "Don't import Suspected Duplicates" option unchecked (it makes far more sense to always have that option checked), in which case Lightroom will import the images from both cards because you've told it to ignore that fact that one card contains duplicates of the other.
Having said that, Lightroom is quite buggy when importing from a direct camera attachment, so even with the duplicates option checked it can still import some of them (just tested with my 5D3 and confirmed that). So do yourself a favour and do as Just Shoot Me recommends and always use a card reader for importing....it's safer and more reliable.
I am having this same issue, I use my card reader to import into Lightroom. I updated the firmware on my camera (same camera) and continue with the same issue.