Adobe .dng files do not show as Thumbnails in Finder
I've recently downloaded some Adobe .dng (raw image files) from their site as part of a Lightroom tutorial, but I find that they do not show up in Finder as thumbnails. They all just show the same icon, (which looks like a camera aperture), and this is not helpful when trying to work out which is which.
Is there any way to get Finder to show them as thumbnails please?
I'm running OS X 10.9.4.
I don't know if it's relevant, but I did have Apple Aperture installed until I uninstalled it recently.
Could uninstalling that have removed raw file handling abilities? On the other hand, when I tried to install the RAWcameraupdate5.04.dmg file from Apple my system advised me that I already had a more recent version installed.
MacBook Pro (15-inch Mid 2010), OS X Mavericks (10.9)