Thank you Arne. I have requested Apple support viewing DNG files created by Silverfast.
Thank you John. Hearing that the problem has a long history, at least I don't feel like there is a way to do this that I am missing.
I also posted "Can a .dng file be viewed in Photos?" in the Apple user discussion group for Photos. A knowledgeable user replied that he has many DNG files in Photos, and Photos displays, edits, and exports them. He noted, "The Photos RAW format support page does not mention DNG format at all, " and that his DNG files had been migrated from Aperture. He says the Aperture RAW format page states:
Aperture works with most DNG files generated from cameras that support this format and with DNG files generated by the Adobe DNG Converter with the “Convert to Linear Image” option turned off.
So Apple system software reads some DNG files, but not all. And we know Apple system software does not read DNG files written by Silverfast. So near but yet so far.
Apple has announced "New editing extensions let you go further with your photos" with the Photos version to be released in the fall of this year with OS X El Capitan (10.11).
OS X El Capitan supports third-party tools that will be available from the Mac App Store and accessible right in the Photos app. Use multiple editing extensions from your favorite developers on a single photo, or use a mix of extensions and the editing tools built into Photos. From adding subtle filters to using beautiful texture effects, you can take your photo editing to a whole new level.
Arne, will LSI create an extension for Photos which will let users edit DNGs created with Silverfast? I suppose the extension would enable editing in Silverfast HDR. If not currently planned, please pass this along as a request for such an extension. As well as benefiting current Silverfast users, the publicity resulting from distribution of such an extension through the Mac App Store could be good for LSI.
Tom