Explain precisely what you mean by "a new format". The rest of your question doesn't really make much sense.

richardplondon wrote:

 

If the filenames of the new pictures are identical to the old pictures, this means they must be in a different folder.

 

If I understand the orignal question properly, a new format means that the file names are not identical, and LR won't find them. DSC_0001.nef and DSC_0001.jpg are not the same filename.

However this whole arrangement sounds to me like a VERY strange way to use Lightroom, and unnecessarily complicated.

This I agree with this more than 300%. I'm guessing, but I think the original poster took some very large RAW photos and turned them into JPGs to save space; and even if that guess is incorrect, that is sad that he wants to do all this huge amount of work recreating a catalog just because he felt the need to change formats. Richardplondon's advice is very good. Lightroom has smarter ways to handle this, and extra hard drive space isn't terribly expensive, especially if you plan to be involved in digital photography.

ianaf100 wrote:

 

Okay, I'll explain it better.

Thanks, that gives us a better idea what you're up to.

I'm going to let John Beardy and/or other folks have a crack at this before I respond further. If you still need to migrate collections when the dust settles, I can help you with that. (I may also be able to help you keep from having to re-upload your photos to smugmug, which would be great if you have thousands - if only hundreds: may not be worth the trouble).

In the mean time, a couple things to consider:

* You already have the very same non-destructive editing capability for the original jpegs as you do for the derived DNGs, so that's not a valid reason to convert format, and because of that: most people do not convert jpegs to DNG.

* However, there are some good reasons to wrap jpegs in a DNG envelope - as you've already mentioned, doing so will common-ize file format and handling, but perhaps more importantly, the DNG can store an edited copy of the jpeg as a preview, thus you can see Lightroom edits outside Lightroom without exporting (provided your viewer will extract and display the embedded preview from the DNG). You will still need to make sure the preview is updated in the DNG which is an operation not unlike exporting (jpeg image data is re-rendered with edits incorporated, but instead of storing in a separate file, Lr embeds the resulting image in the DNG file as a preview).

Disclaimer: I don't use DNG for my files - I'm assuming the above-mentioned things work the same when wrapping jpeg data as raw.

Rob

ianaf100 wrote:

 

Okay, I appreciate the help! 

You bet .

ianaf100 wrote:

 

* You already have the very same non-destructive editing capability for the original jpegs as you do for the derived DNGs, so that's not a valid reason to convert format, and because of that: most people do not convert jpegs to DNG.

...the DNG can store an edited copy of the jpeg as a preview, thus you can see Lightroom edits outside Lightroom without exporting (provided your viewer will extract and display the embedded preview from the DNG).

That's what I meant with DNG's.  You can see the edits out of lightroom without destrutively saving the file.

Most people export instead. Note: Lightroom *never* re-saves edits to jpegs, destructively. If you are nevertheless sure of what you want to do, just be sure you read the fine print. For example, I have *no* viewers installed on my system that could take advantage of such an embedded preview (which couldn't also fold in the Lightroom edits, I mean). *And*, you must update the embedded preview or it won't have the edits (which is nearly equivalent to exporting).

Summary: As long as you know what you are doing, and how Lightroom works..., it's all good as far as I'm concerned, and I'll help. Just want to make sure you aren't about to step on your own toes due to some misunderstanding, eh?

Rob