I think I got bothered more about the Viking helmets because the author said he knew they were wrong, but that people expected them, which somehow seemed the wrong way around. I actually didn't notice the costume errors in the second episode, despite having studied the seventeenth and eighteenth centuries in some depth, so that shows what an Oxford education will do for you... (To be fair I did get annoyed as an undergraduate that serious history books were not illustrated because I wanted to visualise the fashions and furnishings.)