Memory cards

[anglefire]

A faulty memory card won't cause pictures to be "off", focus or otherwise. It can't. It only records, as has been said 0's and 1's. The image file will have a checksum which will be generated when it is produced. If this doesn't match it will come up on the PC as unreadable - and it is why it can be recovered, because the recovery program attempts to recreate the checksum from the available data.

I clean it with a correct spatula and fluid once a year as doing this to often can take the coting off the chip

No it won't. Incorrect fluid or technique can remove the coating - never scrub with the spatula nor use the corner to clean a stubbon bit as the pressure can be massive, cutting through the coating.