I think the OP's issue is he is shooting raw+jpg and saving raw to card 1 and jpg to card 2. In this condition, when he reviews images, he will see the images on card 1 and then when all are jumped through and seen, he will see the images on card 2, essentially dups. While technically speaking nefs can't be seen, that is not the issue. He is simply seeing images on card 1 followed by images on card 2 and he doesn't want to see card 2 images because they are duplicates. I don't think there is any way to block card 2. He could save both raw+jpg on the same card and use card 2 for overflow, but that might not suit his backup needs. Even just shooting raw only with card 2 as backup, you will end up seeing the card 2 pics after you flip through card 1.