By single user I meant that the catalog cannot be open in two machines simultaneously.

I suppose you can put the catalog files in Dropbox to make it available to both computers. Would you share a volume on one computer to the other, or would you use a NAS appliance? You'd have to make sure that the catalog points to the correct folder containing your images in both cases. But you cannot open a catalog that is located on an external networked "shared" drive, like a NAS connected by Ethernet cabling.

Since you mentioned lowest price, many prices and very reasonable price in two sentences, let's start with........price.

Nikon and other importers specify the lowest advertised price authorized dealers can offer. If you see a significantly lower price the lens is probably gray market with questionable if any warranty and Nikon will not repair it under any circumstances. Similar for refurbished, and prices will not vary much from authorized reputable dealers. A few have already been mentioned.

I'm trying to now store all of my original RAW photos and edits on an external hard drive and then clone that drive to another identical external hard drive. The cloning software program I'm using for my PC is called Acronis.

Would it be easier and just as good to just copy any new photos manually to the cloned back up external hard drive rather than using cloning software? My only complaint is that the cloning software stores the photos in a folder, which is in another folder, which is in turn in another folder. Seems a little cumbersome to me.

Also what's the best way to make a copy of your Lightroom catalog to an external HD?

Would appreciate feedback to help me understand what's happening.
I'm in the process of calibrating lenses to a D750 body. I've used both an angled focus chart and the DotTune method and found the DotTune method works better for me.

I noticed two things in this process..
1) I have the camera set to use the AE-L back button focus. If I manually defocus the lens and press the back focus button for less than a half second, the camera mis-focuses. If I press and hold the the back focus button for between 1 and 2 seconds, the camera focuses correctly. Not sure why this is happening.

2) I'm shooting at a target with the camera on a tripod and VR and AF are turned off. I manually focus to critical focus using LiveView. If I then shut LiveView off and take the picture, without refocusing, the actual image in the display is noticeably less sharp than the LiveView image was. Does LiveView apply any in-camera sharpening to the image and if so, is there a way to shut this sharpening off?

Thanks in advance for your responses.

Ken

Had my coffee - Opened up mu W-10 computer, and...
Open File Explorer, then use it to open the folder containing your images. A list of the images by file name appears (at least in my set up)_. Click on an image and you will be presented with a menu. The first selection is "View", select that. View then gives you a list of how the files are to be displayed. I always use "Large Icons" as that fills my screen with as many images as I can comfortably use. Double click on an image and it will fill the screen. The menu bar across the bottom presents a number of options, one of which is Slide Show - just to the right if the red "X" delete icon. Click that and you slide show will begin.