Compact flash cards are extremely reliable, but they can still fail on rare occasions. Sod's law says this will happen at the worst possible time, so it makes sense to take steps to minimise the risks.

The three main safeguards you can take are:

- use a single large card, not multiple smaller ones
- use a USB lead to the camera, not a card-reader
- buy reliable brands

Let's look at each of these in turn, as the reasons may not be immediately obvious ...

A single large card is safer

You might think that using multiple small cards would be safer than a single large card: you avoid putting all your eggs in one basket. If you spread a shoot over say 4 cards, and one of them fails, you've only lost 25% of your photos instead of all of them.

But the reality is different. The biggest threat to the data on a CF card is static discharge, and the time when the cards are most at risk from this is when they are handled. Cards are at their safest when they are inside the camera. Each time you remove or insert a card, you run a small but measurable risk. With a single large card, the card remains safely inside the camera at all times.

Second, every time you remove a card, there is a small chance of losing it. Either immediately - the classic 'dropping it down a drain' scenario - or later, falling out of a pocket or bag.

Third, there is the risk of human error. To protect the integrity of cards, it's good practice to format them before every shoot. If you have multiple cards, there is always the risk of accidentally formatting the wrong card.

Of course, the gold-standard solution is to use a camera like the D3, that can write every photo to two cards. If you shoot weddings, the price of the camera may be slightly less frightening than the risk of losing photos ...

Transfer photos using a USB cable

As already mentioned, cards are safest when inside the camera - so keep them there when you copy the photos to your PC.

If you need an immediate backup, a small laptop is safer than an ImageTank type device, as the latter requires you to remove the card.

Buy reliable brands

It's true that all CF cards are actually made by a very small number of manufacturers, whatever their branding. But this doesn't tell you the whole story.

The big brands will insist on far tighter quality-control standards, for example testing each individual cards. The lesser brands may test one card in 20, or one card in 50.

In the worst case, the cheap brands may actually be the quality-control failures from the more expensive brands.

Given that cards are pretty cheap these days (a 16Gb Sandisk Extreme III can be picked up for about £70), to my mind it doesn't make sense to run the risk.