Today’s Question: When I import my images onto Lightroom [Classic] and request that a backup copy be made on my external drive, those backup images are not DNG as they are in Lightroom, but in a format I do not know and that my computer cannot read. How do I get copies made in a DNG form?
Tim’s Quick Answer: The option to create a second copy of the photos you are importing into your Lightroom Classic catalog will create a copy of exactly what appears on your media card, with the exception that if you rename the photos during import, the backup copies will be renamed. The backup copies, however, will be in the original capture format, even if you use the option to convert to DNG during import into your Lightroom catalog.
More Detail: When you import photos from a media card out of your camera into your Lightroom Classic catalog, you want to copy the photos from the media card to a hard drive being used to store and manage your photos. In addition to simply copying the source capture files, Lightroom also provides the option to convert your proprietary raw captures to the Adobe DNG (Digital Negative) file format.
When you select the “Copy as DNG” option at the top-center of the Import dialog, the conversion to DNG is actually something of a two-step process. First, the original capture files will be copied to the destination storage location you have specified during import. For example, even though you have selected the “Copy as DNG” option, your proprietary raw captures will initially appear in their native file format within Lightroom. After the files are copied to your hard drive they will be converted to the Adobe DNG format, with the original proprietary raw captures discarded.
If you enabled the “Make a Second Copy To” option in the import dialog, that will create an additional copy of the files as they are initially copied to your destination hard drive as part of the import process. In other words, the proprietary raw captures will be copied to the backup location in the same proprietary raw format. If you have selected the option to rename photos during import, the backup copy will reflect that renaming as well. But the backup copies will not be converted to the Adobe DNG file format.
If you want to make an additional copy of the DNG versions of the photos created as part of the overall import process, you would need to back them up in some way as part of a follow-up process. For example, you could select all of the photos that had just been imported, and export a copy of those files using the “Original” option from the Image Format popup in the File Settings section of the Export dialog. You could also simply create an updated backup of your primary storage, such as by using GoodSync (http://timgrey.me/greybackup), the synchronization backup software I recommend for backing up photo storage.