Losing a card alarms people more than losing a drive. Partly that is because a shoot cannot be taken again, and partly it is the wording — the warning reads as though the pictures had already been destroyed. Nine times in ten they are precisely where the camera put them, untouched.
Open a card up conceptually and there are three separate things in it. At the bottom, NAND flash dies, where each photograph exists as trapped charge. In the middle, a controller — a small processor that maps the addresses a camera asks about onto real cells, distributes writing so that no single region wears out first, and quietly retires blocks that have failed. On top, a file system, FAT32 on the smaller capacities and exFAT above 32GB, which does nothing more than list each file with its name, its length and where it starts.
Compare the sizes. That top layer occupies a few hundred kilobytes and describes tens of gigabytes of images. It is also the layer that fails, and the reason is simple wear: it gets rewritten on every single save and every single delete, whereas the photographs are written once and then never touched again. Yank a card out during a write, run the battery flat mid-burst, or let dirty contacts drop the connection at the wrong instant, and the index is what comes apart.
A computer confronted with that finds no file system it recognises. It reasonably concludes there is nothing there and offers to set one up for you. At the moment that dialogue appears, not one image has been altered.
Say yes to the format and a fresh, empty index goes down on top of the damaged one. That shuts off the quick route home and leaves only the slow one. Slide the card back into the camera to check it still works and the frame you take is written into whichever blocks the controller currently believes are spare — and wear levelling means you have no influence at all over where on the card those blocks physically sit. One test shot can land in the middle of the wedding. Neither move can be undone, by anyone, for any fee.
Which makes the correct response the one that feels like giving up. Take the card out, put it somewhere it will not get picked up again, and stop touching it. Nothing degrades while a card sits in a drawer. The photographs stay where the camera wrote them and the odds stay exactly as good as they are now.
Windows sometimes offers to scan and fix the card rather than format it, and the answer there is the same one. Utilities of that kind exist to leave a file system internally consistent, not complete, and consistency is achieved by throwing away whatever will not reconcile. The argument is set out at length in what CHKDSK costs you, and it applies to cards word for word.
Before assuming the worst, rule out the boring possibilities, because between them they account for a good share of these calls and none of the checks writes anything.
The lock switch. Full-size SD cards carry a small sliding tab down one edge. It gets knocked into the locked position by everything else in a camera bag, and a locked card reads unpredictably or refuses outright. Dirty contacts. Skin oil, dust and the residue of a damp morning all interfere with the connection, and a dry cloth deals with it for nothing.
The reader. This causes far more trouble than it is given credit for. The sprung contacts in an inexpensive adapter go slack after a few hundred insertions, and the slot in a laptop that has taken thousands of cards is no better; either will throw read errors on media a decent powered reader handles without complaint. Try the card in a different reader on a different computer before drawing any conclusion about the card.
A counterfeit. This one explains an entire family of failures that look like corruption and are nothing of the kind. Cards bought very cheaply from online marketplaces are often fakes whose controllers have been reprogrammed to advertise a capacity the flash simply does not possess. Something sold as 512GB may hold 32GB. It accepts everything you shoot and silently throws away or overwrites the surplus, behaving perfectly until you try to read back the later files. Cheap card, trouble starting the moment it filled up — that is almost certainly what happened, and nothing recovers data that was never written anywhere.
Four symptoms belong together: a format that fails, a capacity reported as some fraction of the real one, a card announcing itself as 0MB, and a card that has become permanently read-only. All four are the controller talking, not the flash. These chips are designed to drop into a locked read-only state once their internal error and wear counters pass a threshold — a deliberate last stand intended to preserve whatever is on board — and they lose their address translation tables outright if power disappears at the wrong microsecond. In both cases the part in the middle has stopped behaving predictably, and no consumer utility gets past it. The low-level formatting tools that forums recommend for this are a reliable method of destroying a card that still contains something you want.
The way through is around the controller rather than through it. Where it still answers at all, the card gets imaged behind a write blocker in slow, repeated passes that tolerate errors instead of stopping at them. Where it answers not at all, the flash itself is read with a specialist programmer, and only then does the difficult part begin — the scrambling pattern, the way consecutive data is spread across dies and planes, and the error-correction scheme all have to be worked out from scratch before anything that looks like a photograph emerges.
Construction matters here. A full-size SD card usually keeps its flash and its controller in separate packages. Most microSD cards are monolithic: die and controller moulded into one body, so the read has to be taken from test pads on the outside. That is chip-level work, which appears in the published exclusions from no fix, no fee and carries 50% of the figure upfront. It is also the reason a cracked card, or one with damaged contacts, should be left completely alone — one more flex and the bond wires inside go.
Nothing happens to your card beyond being read. A full sector-level copy is taken first, through a write blocker, and every decision from that point on is made against the copy. Two things follow: a card already in decline is never pushed any further by the recovery itself, and no error at this end can reach the original.
If enough of the index survives inside that copy, it gets repaired and the folder structure returns looking the way the camera left it, filenames and all. If it does not, the images are found by their contents instead. A JPEG opens with a recognisable byte sequence, and so do CR3, NEF, ARW and every other raw format worth having, which means frames can be lifted out of unallocated space with no index in existence at all. The cost of that route is the naming: carved files come back numbered rather than named, which some people mind and others do not.
Two checks happen before anything is called recovered. Every still is opened and rendered rather than merely listed, because a filename appearing in a results pane and an image that actually draws on screen are two different claims. And video gets particular attention, since long clips occupy scattered blocks and a partial overwrite tends to wreck something in the middle of a file rather than remove it tidily — which is one more argument for not shooting anything else on a card that has started behaving oddly.
The cards that reach this bench from Leicestershire follow a fairly steady pattern. Wedding and event photographers across the county. Dashcam and site survey footage. Drone cards off agricultural and construction work out towards Melton Mowbray and Market Harborough. Students on the media courses at De Montfort with an entire term of field recordings on one card and no second copy anywhere. They spend their lives in bags, get changed with cold fingers on wet mornings, absorb damp that never really leaves, and pass through several thousand insertion cycles that the contacts were never rated for.
Packing takes two minutes. Sandwich the card between folded pieces of stiff cardboard so that it cannot bend, put that inside a padded envelope, and send it tracked to Cambridge Data Recovery, Compass House, Vision Park, Chivers Way, Cambridge CB24 9AD. Postage on something that light is pennies. Driving is an option — around seventy miles, M1 south to Junction 19 and then the A14 east, with the lab two minutes off Junction 32 and parking at the door — and the reception desk signs devices in Mon–Fri 9:00am–5:30pm. There is no Leicester counter and nobody collects.
The band is £250 + VAT for memory cards, USB sticks and pen drives. Assessment costs nothing and finishes 2 working days from booking in, the price is settled in writing before anything chargeable starts, and finished work is normally back inside 2 to 4 working days. Where the read has to be taken off the silicon it is chip-level work, one of the published exclusions from no fix, no fee, and half the figure is payable upfront. Alongside this page sit memory card recovery, recovering a formatted SD card, USB stick recovery and data recovery cost. The freephone is 0800 689 0668, Mon–Fri 9:00am–5:30pm.
Doing nothing is the most productive thing available to you here. That format prompt is describing a torn index, and behind it every frame is lying where the camera put it. It will stay there indefinitely, right up until something writes over it. Take the card out, leave it out, and let a copy carry all the risk instead.
Diagnosis costs nothing and finishes 2 working days from the moment Cambridge books your device in. The figure after that is written down and fixed. £250 + VAT a card or stick, £300 + VAT one drive or SSD.