searching assets - using related entry slug
I have not tried this against a working database but based on something very similar this should work:

{% set matchingPhotos = craft.assets.folderId(5).relatedTo({
  targetElement: craft.entries({
    slug : 'example-photographer',
    section : 'photographers'
  }),
  field : assetsPhotographerField
}) %}


In reverse what you are doing is getting all the photographer entries that match that slug that are related to the assets field in that specific folder id...does that make any sense?!

You may need to swap targetElement out for sourceElement - I never know which way round it should be!