Can I use large capacity CompactFlash cards in my PowerShot?
Canon recommends and supports the PowerShot cameras only with it’s own cards, however some other CompactFlash cards do indeed work. CAUTION: Not all CompactFlash cards are equal, the variations in read/write speeds is one factor, also consider the different power consumptions. We have even heard of 5volt and 3.3volt cards, though the standard covers both in the same card. For example we have successfully tried a 45MB Sandisk card in a PowerShot 600, and a PowerShot A5.