LrC - Find images with the same name but different extension

And the Plugin - "Teekesselchen Duplicate Finder" - is very capable of finding only imagers that have the same Filename. Just use the one 'Rule' = [Filename]. Let it tag images with the Keyword "Duplicates", and also create a Smart Collection of images with KW "Duplicate".

The Plugin does not delete photos- Just tags them for you to decide their fate..

Duplicate Photos (Lightroom Queen)

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"to find files that have the same name but a different extension?"

To find all DNG / TIFF pairs, run this Any Filter query:

Note each DNG / TIFF pair must reside in the same folder.

@mhump 

What is the purpose of converting a TIF file to DNG?

I thought that is the case, but figured i'd make sure i'm not missing something.

The real issue I am trying to solve is dealing with "duplicates" after I convert TIFs to DNGs.  I use the export feature, which adds the new DNG into the catalog, but there is no option to add them to the collections (I would love an "Add to same collections" option in the Export dialog).

Once they are in DNG, I no longer need the TIF and so I delete it.  But I want to make sure that the DNG version is included in all of the same collections that the original TIF was.  How I do it now is to each TIF, note which collections it is in and then add the DNG to each.  It's a little tedius if I have more than a few images, and prone to mistakes.

I don't know.  Maybe there is a better workflow for this.

You can't search on something like 'has same file name' without entering a name, but you can just sort the grid by file name (bottom left).