DarkTable Tethering - Nikon D7200 - Error 53

I was trying to connect my Nikon D7200 DSLR camera to my Ubuntu 16.04 box and tether it to DarkTable so that I could control the camera with/from the computer.  When I plugged my camera into the USB port, Ubuntu didn't recognized it but mounted the camera's two memory cards as removable hard drive.  I could access the memory cards with Nautilus and move files to and from the cards just fine.  However when I launched DarkTable I got the error "Error initializing camera: -53: Could not claim the USB device".  To fix this all I had to do was open Nautilus, right click on the two memory cards and select "Unmount".  After Unmounting the two memory cards I launch DarkTable, selected the Tethering Tab and it worked flawlessly. I'll have to unmount the memory cards every time I plug the camera in but it's not that hard and it works  

For those of you who don't know, DarkTable is photo post processing software.  It competes with Adobe Lightroom and I think you can do more with it than Lightroom.  If you capture your photos with your DSLR camera in the RAW format you adjust the colors, exposures, saturation, and much, much more.  You can still adjust JPG photos too but not as much or as nice as you can with the RAW format.  Trust me, if you've spent the money on a good DSLR camera, capture your photos in RAW.  DarkTable allows you to export your RAW format files (DNG, NIK, CRW, CR2) to JPG's after you've adjusted them.

The RAW format of your DSLR captures and stores much more information than JPG.  So even if you do nothing with RAW images other than convert a copy of it to JPG keep/shoot in the RAW format so that you'll have captured the data to use later when you learn how to use a program like DarkTable.

A Bonus Tip:  If you use Photoshop CS6 (the last own it non-cloud version)  you can install Adobe's Camera Raw Plug-in and get a lot of Lightroom ($10 monthly) / DarkTable (Free) function to use with your RAW images inside Photoshop CS6.  The CS6 version is 9.11 (near the bottom of the page).