First, go to the Sandisk website and look for a free image file recovery software there. I know they offer one for folks using their memory cards. I have similar software from Lexar installed on my computer and have used it a couple times with partial success.
DO NOT format your memory card until you have tried the image recovery process. However, if you ever accidentally do format a card in error, until you actually start to take photos again, likely you would be able to recover many of the older files on the card.
I format every memory card in the camera before first use AND before every use there-after. (See below.)
I agree that you should get and use smaller memory cards.You have 6 months or more worth of photographs on an easily lost, little memory card! You also need to copy those images to your computer much, much more often.
I shoot sporting events with two or three cameras, sometimes even with four... frequently taking 1500, 3000, 6000 or more images in a day. I have twenty memory cards, all 32GB. Each camera holds two cards, although normally I don't back up images in-camera. But if it's an important shoot, I will switch to backing up the images in-camera.
My Canon camera that produces 24MP images like your SL3 gets roughly 900 RAW files per 32GB memory card. I don't know how many JPEGs the card would hold, but am sure it would be quite a few more than that. I use card cases to store my memory cards and have a simple method of placing the cards face up when they are ready to use, face down when they are full of fresh images.
I almost always download images promptly the same day they're taken. I never use WiFi or the USB cable from the camera. I always use a memory card reader. It's by far the safest and usually the fastest way to do downloads.
To get the images onto my computer I don't do anything fancy... I just use the computer' operating system to copy images from the memory card to a folder I've prepared for them on my computer. I don't trust fancy software that tries to control downloads. And, once again, I COPY the image files... I don't move them. This leaves the originals on the memory card until I can check them on the computer and back them up. That's a good precaution, just in case something goes wrong with the copy process.
Once all the images have been copied off my memory cards, I just leave the old files on them and put them back in their case face up. Then when I go to use them, I always format them.
With perhaps 100+ memory cards I've used over the years, many of them with a lot of repeated use, I have had exactly two cards fail. One of those wouldn't work at all, right out of the package. The other worked once and then "locked up". It so happened I'd lent it to someone who was helping me shoot an event, so I have no idea what they did with it. We were able to download the JPEG files from it, but after that could not get the RAW files or reformat it.
The only time I have had corrupted files on a memory card, it was my own fault for opening the memory card door and ejecting a card while the camera was still writing to the card (newer cameras write so fast, that's not a problem). I also had one download "fail", but it also was my own fault. I had connected something to my computer and didn't have enough USB ports, so I got a USB hub. The card reader I was using at the time didn't like being connected through that hub, so I had a bunch of files show corruption. As soon as I reconnected the card reader directly to the computer again, the problem was solved.
To recap:
- First get the recovery software from Sandisk and try to recover the image files already on that gigantic memory card.
- Then get yourself some smaller memory cards... maybe 32GB, 64GB?
- Then be sure to format the cards in your camera before using them.
- I also recommend some kind of case to keep your cards organized
- Also write your name and email or phone number on each card, in case you lose it and someone finds it.
- Then copy your image files off of your cards more frequently....- the longer you leave them on the card and haven't copied to your computer, the more risk of losing them.
- I also highly recommend you get organized on your computer. It's best to do so at the beginning, before you have tens of thousands of images!
- AND back up your image files, maybe to "the cloud" or on an external drive. I buy two drives and keep one off site, then swap them out every couple weeks. That way if anything happens to one of them, that's the most I'll lose.
I hope this helps and solves your problem.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2), EOS M5, some other cameras, various lenses & accessories
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