I have the following issue with my ND filters 100x100 square (K&F concept), I am using them with my Sony A7 and with several manual lenses: when I am using the ND1000 alone I do not have any issue, it doesn't matter which lens I am using
When I am using two filter the ND1000+ND64 I start to get issues with 2 lenses, the Canon FD 20mm f2.4 and the Canon FD 100-300 f5.6; all the pictures are partly washed out. I tried different angles, different time during the day but more or less I am getting always the same result, washed out pictures.
When I am using the Flektogon 35mm or Helios 58mm or Sony 50mm I don't have any issue with the ND1000+ND64. I tried to realized a hood to cover the filter (made by paper), it helped a bit but not really a noticeable difference. I don't know how to solve this issue.
I do know that ND filter are not really great with wide angle lenses and that can explain the issue with the 20mm but what about my 100-300 mm (btw the issue is more visible at 300mm rather than 100mm)/
Any idea? potential solutions?