Brian (p4pictures, EOS specialist trainer, photographer and author), you wrote: "Are you using a camera with two card slots, and are you recording to both cards? If this is the case then the images you delete on the camera are only deleted from one of the two cards. With two cards configured to either put a RAW and JPG on separate cards, or to write the same files to both cards you will have a card set as the "playback card". When you press the delete button on the camera the images are deleted from the playback card only. If you now take out one of the cards from the camera and put it in the computer then it is possible that it's the card that didn't have the files deleted. This is also the case for in-camera image ratings. Ratings are only applied to the images on the playback card, not the other."
I just discovered this very important, basic camera functionality today, after several years of shooting with Canon's R3 and, more recently, also with Canon's R1. I set up Card 2 on both the Canon R3 and also the Canon R1 to record a backup copy of everything that is on Card 1 (my playback drive). Even though I had not realized it, what you wrote had been hidden from me for years because, since Card 2 on the Canon R3 is a much slower SD/SDHC/SDXC memory card drive than is Card 1 (a CFexpress drive). I had set Drive 2 to record my backups of Card 1 (RAW images) in a smaller file size (Large JPEGs), so that I would not slow down my ability to shoot and record RAW images (on Card 1) and their backups (on Card 2) simultaneously.
Recently I got a Canon R1, which has two CFexpress memory card drives, so I was finally able to record simultaneous backup RAW images to Card 2. However, since both cards were now recording the same RAW images, I could not understand why the total size of the files differed on the two drives. I thought that it had something to do with me occasionally shooting stills and videos simultaneously on the R1, a capability which the R3 does not have (to do this, one must select the video position on the two-position, stills or video switch, which is located immediately to the right of the viewfinder). The way that new functionality works is it records the videos on one card and the simultaneous stills on the other. That produces different total file sizes on the two card drives.
However, I just completed a shoot with the R1 where I did not shoot any of those simultaneous stills and videos, so I expected Card 2 to have exactly the same images and total file size as Card 1, but after I transferred Card 1 I discovered that Card 2 actually had more images than Card 1. As you explained, that was because images that I had deleted from Card 1 (my playback drive) while I was on my shoot had not been deleted from Card 2 (my backup drive). I only discovered this today (on my own) because I had set my import procedure in Lightroom Classic to NOT IMPORT DUPLICATES. That way I could easily transfer only the images (videos or still, I do not remember which) that are not on Card 1, when I record both stills and videos simultaneously. Today, as a safety check before I formatted both memory cards, I prepared to import any non-duplicates from Card 2 — and I discovered that there were some! It was only then that I realized that the only non-duplicates on Card 2 were photos that I had deleted (only from Card 1, as it turns out) while on my shoot.
I also did not know, until you said so, that my ratings that I apply to photos while on my shoots were only being recorded on Card 1. So much for having a full backup of Card 1.
This was very confusing until I finally realized (today) what has been happening for years, since I began shooting with the Canon R3.
Jan
