Quote Originally Posted by Jim Noel View Post
Half plate is approximately 4.5 x 6.5 so the answer is "No" it will not take a 5x7 back.
Sorry it will, as I explained earlier, the British bookform holders were very much larger than modern International half plate and 7x5 DDS which have the same outside dimensions.

In fact I've seen an Ebay seller (who happens to be a friend) post a sale on ebay showing a 7x5 darkslide sitting where a book form half plate holer would slot, it wouldn't be light tight though.