problem in getting photos on my "photos" app on my imac to my desktop

norm colorado wrote: …i am trying to move photos from the photos app to my imac desktop

Somehow Photos seems to have lost track of the Original picture files that are used to construct the pictures that you view and export. There are a couple of things to address:

#1 If by "move Photos" you mean drag & drop, then that's a bad idea. Drag & drop probably doesn't get you full resolution images. See this:

Should you use Drag & Drop in Photos? - Apple Community

If you decide to go through Finder, then you should use File>Export>Export Unmodified Original.

#2 To edit pictures in Lightroom, you would normally use "Photos>Image>Edit with

With Lightroom, you'll have to save the image to Finder and then re-import the new file.

#3 Check to see if you have "Copy Items" checked at Photos Settings>General:

If that has somehow become unchecked, then that needs to be fixed, and you may be in for more trouble. If this was unchecked, then you must search around your Mac to find the "IMG_1730.DNG" file. If you find one, it will help with others.

You don't say if you're using iCloud Photos or Optimize Storage. What's going on depends on this information.

Let us know about iCloud and this:

• How did these pictures get into Photos? iCloud? from a camera's SD card? Transfer from a computer? what?
• Do you have more than one Photos Library? 
• Where does your Mac's Photos Library reside-- in the Pictures folder of your internal drive, or on an external drive? or on a network? on iCloud drive?
• What is your storage on this Mac? At System Settings>General> Storage, my Mac says 745 GB of 1TBB used. What does yours say?

If we know this stuff, we may be able to help.

In a nutshell:

You're running a Referenced Library with the original files stored on an external volume. A recipe for disaster.

A Referenced Library is when you don't copy the original files into the Photo Library package on import. The problem with doing this (as you're discovering) is that Photos does not have the tools to manage this set up. Should the path to the file change for any reason you have a problem, and the path will change at some point if you store the files on an external volume. Every time this happens you will need to reconnect to the original file for each and every file. Sometimes for the same file, many times. Frankly, my solid advice is as follows: If you want to use Photos don't use a referenced Library. If you want to have a referenced library, don't use Photos.

A general comment:

Using Photos and LRC makes no sense. LRC is a better photo manager (and has the tools to work with a referenced library) and a much more powerful editor. LRC is the app you're paying for and is far more capable. It's like using a children's pedal car to drive to work when you have a BMW outside the door.

Why are you sending the files to LRC? If you're migrating from Photos to LRC then there is a plug-in in LRC for that, though you would need to fix your Photos Library for that to work.

Are you trying to edit them in LRC? Using LRC as an external editor in Photos is needlessly complex as both apps are parametric processers and cannot speak to each other. Solution to that would be to move to LRC.

norm colorado wrote: …that box is unchecked.

As everyone posting here has repeated, that's bad. Do you know when you unchecked it? See this to help with understanding how the Photo Library works, and about Referenced and Managed Libraries:

Basic Concepts and Terms About Photos - Apple Community

Pictures you see on the screen are a combination of the information in the database and the Original imported file. Because "copy" was not checked, the original picture files were not copied to the Library, and you have to find them. If you can't--if they were erased, for instance, then you may be able to recover some lower resolution images.

I don't understand this statement: "i am not using icloud photos as far as i know. i have less than 100 photos on iCloud." It seems like both can't be true.

The pictures at iCloud.com will be complete and will have the Original files.

Are you possible running a referenced library as opposed to a managed library:

Is the check box checked or not?

norm colorado wrote:

i will stick w/LRC for my editing

LR by default behaves about the same as Photos in this regard.

...I use Adobe Lightroom to edit raw before importing edited .jpg to Photos. By default LR uses a referenced library i.e. the actual raws are in their own folder (and the edited .jpg goes there by default). ...after I delete that original raw folder, LR no longer can edit them unless I copy it from the backup and also preserve or also copy ~/Pictures/Lightroom folder which holds the edit info.

So whatever app you use, make sure to check your workflow works.

I work kind of like Matti, but normally for me, RAW images never see the Photos app. My Nikons have two SD cards, and I use one for jpgs and the other for RAW. I import the jpgs to Photos, and I do some editing and, especially, selecting of the best ones, there-- like this:

Choosing Favorites using Keywords in Mac … - Apple Community

Fewer than 1 in 5 are favorites.

I import the RAWs into Lightroom, and there I may edit the potential favorites that I think will benefit from RAW development using greater exposure control and masking. These pictures I export as 100% jpgs, and I import those to Photos. Only the favorites go into the Photos Library that I connect to iCloud and my iPhone and iPad. I use Photos to organize the pictures like this:

Organizing Photos with Folders & Albums - Apple Community

(This business of using Photos and Lightroom seems to drive Yer_Man crazy…)