I keep seeing different information about what the filter factor is for a yellow #8 filter. The one I have is actually made by Hoya and they call it a yellow K2, but it's the same as a Wratten #8 apparently. ONe book said that there is no filter factor for this filter. But online I saw several charts that said the filter factor is 2. When I metered through the filter, the reading for a shadow area was 7.6, whereas it was 8 without the filter. But somebody said that meters are unreliable, particularly older ones, when it comes to reading through filters. So I wonder what filter factor to use.